Deformation prediction method for front support point hanging basket cantilever construction process based on finite element simulation

Abstract

This invention discloses a deformation prediction method for cantilever construction using a front-support hanging basket based on finite element simulation, belonging to the field of numerical analysis technology for construction control. It obtains the strength characteristics and ductile deformation properties of engineering cement-based composite materials and constructs a constitutive model of ECC materials. Through experimental research, it studies the static shear performance of short studs in steel-ECC composite structures and analyzes the influence of interlayer bonding. It obtains the local bending performance of the steel-ECC composite structure under positive and negative bending moment loading conditions, establishes bending performance parameters and a finite element model of the cantilever construction process using a front-support hanging basket, inputs constitutive and performance parameters, and simulates the movement of the hanging basket, segmental casting, and prestressing tension stage by stage, calculating the deformation amount at each construction stage and outputting the predicted deformation value. This invention can precisely consider the nonlinearity of ECC materials, the slippage of the steel-ECC interface, and the time-varying characteristics of the construction process, significantly improving the accuracy of deformation prediction in cantilever construction and providing a reliable basis for formwork elevation adjustment and construction control.

Description

Technical Field

[0001] This invention seeks to protect a method for predicting deformation during the cantilever construction process of a front-support hanging basket based on finite element simulation, which belongs to the field of numerical analysis technology for construction control. Background Technology

[0002] The cantilever construction with formwork at the front support point is a key technology in the construction of prestressed concrete bridges. Its construction process includes multiple stages such as moving the formwork forward, segmental casting, and prestressing tensioning. Deformation control at each stage directly affects the bridge's final alignment and structural safety. Existing methods for predicting construction deformation are mostly based on empirical formulas or simplified mechanical models, such as using elastic theory to estimate formwork deformation or treating concrete as a homogeneous linear elastic material for rough calculations. However, in actual construction, factors such as material nonlinearity, interface slip, and time-varying effects significantly influence the deformation development pattern. Traditional methods struggle to accurately predict the cumulative deformation of each segment, leading to reliance on on-site measurements and empirical corrections for formwork elevation adjustments, increasing construction risks and time costs.

[0003] Engineering cement-based composite materials (ECCs) are increasingly being used in bridge joints, reinforcement, and composite components due to their excellent tensile strain hardening characteristics and multi-slot cracking behavior. Steel-ECC composite structures can fully utilize the tensile strength of steel and the high ductility of ECC, effectively improving the brittle cracking problem of traditional steel-concrete composite structures. Current research on ECC materials mainly focuses on its basic mechanical property tests, including compression tests, direct tensile tests, and four-point bending tests. However, research on incorporating the material constitutive models obtained from these tests into finite element simulations of the construction process is still insufficient. Furthermore, while reports have been made on the shear resistance of short studs in steel-ECC composite structures and the local bending resistance of composite beams under positive and negative bending moments using push-out and four-point bending tests, there is a lack of systematic methodological guidance on how to connect these microscopic performance parameters with segment-by-segment deformation prediction in cantilever construction.

[0004] Existing finite element method (FEM) simulation techniques for construction process analysis mostly employ idealized material models and boundary conditions, neglecting the nonlinear behavior of bond slip between steel and ECC layers and the gradual changes in material properties at different construction stages. For the specific structural form of the front-support hanging basket, standardized simulation methods for front-support anchorage, rear-anchor constraint, and segment-by-segment movement have not yet been established, particularly lacking in comprehensive modeling that includes ECC material constitutives, short stud spring elements, and contact property definitions. Therefore, a deformation prediction method for the cantilever construction process of the front-support hanging basket based on finite element simulation is needed. This method would combine ECC material testing, steel-ECC composite structure performance testing, and nonlinear finite element analysis of the construction process to achieve accurate prediction of deformation at each construction stage, providing a basis for adjusting formwork elevation and construction control. Summary of the Invention

[0005] According to a first aspect of the present invention, the present invention claims protection for a method for predicting deformation during the cantilever construction process of a front-support hanging basket based on finite element simulation, comprising the following steps: S1: Obtain the compressive strength, tensile strength, and flexural strength of the engineering cement-based ECC composite material, determine the strength characteristics and ductile deformation properties based on the stress-strain curves obtained from the experiment, and construct the constitutive model of the ECC material; S2: Obtain the static shear performance of short studs in steel-ECC composite structures, measure the shear capacity, shear stiffness and slip capacity of the ejected specimens, analyze the influence of interlaminar bond between steel and ECC on shear performance, and obtain the static shear parameters of short studs; S3: Obtain the local bending performance of the steel-ECC composite structure under positive and negative bending moment loading conditions. Measure the bending capacity, relative slip capacity, and crack resistance of the composite structure under different protective layer thicknesses and reinforcement ratios to obtain the local bending performance parameters under positive and negative bending moment loading conditions. S4: Establish a finite element model of the cantilever construction process of the front support hanging basket, and input the constitutive model of the ECC material, static shear parameters and local bending performance parameters into the finite element model; S5: Simulate the cantilever construction process of the front support hanging basket, including moving the hanging basket segment by segment, pouring concrete segment by segment, and tensioning prestress segment by segment, and calculate the deformation of each construction stage. S6: Output the predicted deformation value of the cantilever construction process of the front support hanging basket based on the deformation amount of each construction stage.

[0006] Furthermore, in S1, a prism specimen is used, and axial pressure is applied until the specimen fails. The peak load and the corresponding axial compressive strain are recorded, and the compressive strength is calculated based on the ratio of the peak load to the bearing area of ​​the specimen. A dog-bone shaped plate specimen was used. Axial tension was applied to both ends of the specimen, and tensile strain within the gauge length was measured using an extensometer to obtain the full curve of tensile stress versus tensile strain. The elastic modulus, peak tensile stress, and ultimate tensile strain were extracted from the full curve as parameters for tensile strength characteristics and ductile deformation properties. A beam-type specimen was used, and two symmetrical loads were applied to the mid-span region at the bottom of the specimen. The relationship curve between the load and the mid-span deflection was measured. The bending strength and bending toughness index were calculated according to the bending stress formula. The bending toughness index was determined by the ratio of the area under the load-deflection curve to the area corresponding to the first cracking load.

[0007] Furthermore, S2 includes the following operations: Prepare a steel-ECC composite specimen by welding short studs to the upper surface of the steel plate and casting ECC material on top of the steel plate to form an ECC plate, so that the short studs are completely embedded in the ECC plate; The ejected specimen was installed in a universal testing machine. A vertical ejection load was applied to the end of the steel plate. Two linear variable differential transformers were symmetrically arranged on both sides of the specimen to measure the relative slip between the steel plate and the ECC plate. Continuous loading was performed using displacement control, and the load-slip curves were recorded throughout the entire process. Shear capacity is extracted from the load-slip curve as the peak load value of the curve, shear stiffness is extracted as the slope value of the straight part of the rising segment of the curve, and slip capacity is extracted as the slip amount corresponding to the peak load and the ultimate slip amount. By preparing multiple sets of ejection specimens with different interface treatments, comparing the differences in load-slip curves among the specimens, analyzing the influence of interlaminar bonding on shear capacity, shear stiffness, and slippage capacity, and obtaining modified static shear parameters considering the interlaminar bonding effect.

[0008] Further, S3 includes: Steel-ECC composite beam specimens were prepared, with multiple different values ​​for protective layer thickness and multiple different values ​​for reinforcement ratio; For positive bending moment loading, the composite beam specimen is simply supported on two supports, and vertical loads are applied at two symmetrical points in the mid-span region of the beam, so that the bottom steel plate of the beam is under tension and the top ECC is under compression. For negative bending moment loading, the two ends of the composite beam specimen are constrained by fixed supports, and vertical loads are applied at two symmetrical points in the mid-span region of the beam, so that the top ECC of the beam is under tension and the bottom steel plate is under compression. Alternatively, the original positive bending moment specimen can be flipped over and loaded using an inverted simply supported method. Displacement control mode was used during both positive and negative bending moment loading processes. The loading rate was controlled to keep the rate of increase of mid-span deflection constant. The load values ​​of the load sensor, the deflection values ​​of the linear variable differential transformer arranged at mid-span, the relative slip of the slip measurement points arranged on multiple sections along the beam length, and the development of surface cracks in the ECC layer were continuously recorded. The flexural bearing capacity is determined based on the recorded load-mid-span deflection curve. The flexural bearing capacity includes the cracking load value when the first crack appears, the peak load value on the curve, and the residual load value corresponding to a specific deflection-ductility ratio after the peak load. Based on the relative slip measured at multiple cross sections, a slip distribution curve along the beam length is plotted, and the maximum slip is extracted from the distribution curve as the relative slip capacity of the specimen. During the loading process, the load value at which the first visible crack appeared on the surface of the ECC layer was recorded using a magnifying glass and a crack observation instrument as the crack initiation load. The average and maximum values ​​of the crack spacing were measured, and the rate of change of the crack width with the increase of the load was measured to obtain crack resistance indicators including crack initiation load, crack spacing range, and crack width growth rate. The flexural bearing capacity, relative slip capacity, and crack resistance obtained under all positive bending moment conditions are summarized as local flexural performance parameters under positive bending moment conditions, and the corresponding indices obtained under all negative bending moment conditions are summarized as local flexural performance parameters under negative bending moment conditions.

[0009] Further, S4 includes: A three-dimensional geometric model was established based on the structural design drawings of the front support hanging basket and the construction drawings of the bridge cantilever segment; The main truss members of the hanging basket are meshed using beam elements, the front support anchor rods and rear anchor threaded steel bars are meshed using rod elements, the traveling track is meshed using shell elements, the concrete box girder segments are meshed using solid elements, and the steel plates in the steel-ECC composite structure area are meshed using shell elements, the ECC layer is meshed using solid elements, and the short studs are meshed using spring elements. A contact pair is established on the contact surface between the steel plate element and the solid element of the ECC layer. The normal behavior of the contact pair is defined as hard contact, and the tangential behavior is defined as penalty friction. The static shear parameters obtained from the push-out test are converted into the stiffness properties of the spring element or the bond slip constitutive curve of the contact pair. The constitutive model of ECC material is assigned to the solid elements of ECC layer, and the bilinear elastoplastic constitutive model of steel is assigned to the steel plate shell elements and steel bar elements. Displacement constraints are applied at the boundaries of the model, including fixed-end constraints at the ends of the zero block segments that have been poured, vertical and longitudinal fixed constraints at the anchor points of the hanging basket, and rolling support constraints that allow only vertical movement at the front support points of the hanging basket.

[0010] Further, S5 includes: Before the finite element analysis of the current construction phase begins, the hanging basket model element is activated and moved from the previous segment position to the current segment position. The moving operation is achieved by changing the node coordinates of the hanging basket element and regenerating the element connection relationship. Activate the concrete box girder solid element and steel bar element of the current segment, and at the same time activate the longitudinal prestressed duct element and prestressed steel strand element inside the current segment; After the current segment unit is activated, apply the self-weight load of the concrete in the current segment and apply the construction live load to the hanging formwork system. Perform finite element analysis for the current construction phase, use an incremental iterative solver to calculate the structural displacement field and stress field at the end of the phase, and extract the vertical displacements of the upper and lower edges of the front section of the current segment as the deformation for this phase from the solution results. After solving for the concrete self-weight and construction live load, a prestressing tension simulation is performed. The prestressing tension force is applied to the end nodes of the prestressed steel strand element in the form of an equivalent nodal load, or a temperature load is applied to the steel strand element using the cooling method to simulate the prestressing effect. The finite element solution is performed again to obtain the structural deformation increment after tensioning. This increment is added to the deformation before tensioning to obtain the final deformation of this stage. The displacement and stress values ​​of all nodes obtained in the current stage are saved as the initial state for the next stage, while the hanging basket element is blunted to simulate the process of the hanging basket moving forward to the next segment. Repeat the above activation, loading, solving, saving, and passivation operations until the construction stage simulation of all cantilevered segments is completed.

[0011] Further, S6 includes: The deformation of multiple key nodes is extracted from the post-processing results of the finite element model, and the extracted deformation is arranged to generate a sequence of data showing the change of deformation of each key node with the construction stage. For each construction stage, calculate the predicted vertical deflection and horizontal displacement of the front section of the current segment; Calculate the elastic deformation of the node at the front support point of the hanging basket and the axial deformation of each member of the main truss of the hanging basket. Use the elastic deformation of the front support point as the predicted deformation value of the hanging basket system. The deformation under different load conditions within the same construction stage is linearly superimposed. For the steel-ECC composite structure area, the relative displacement vector between the steel plate shell unit node and the adjacent ECC solid unit node in each construction stage is extracted. The component of the relative displacement vector in the tangential direction is calculated as the predicted value of inter-story slip, and the distribution curve of slip along the beam length is output. Output deformation prediction result file, recording the deformation values ​​of all key nodes in each construction stage, the overall deformation cloud map data of the structure after each construction stage, and the inter-story slip distribution data of the steel-ECC composite structure area after each construction stage. Calculate the deformation increment sequence between two adjacent construction stages and compare each deformation increment with the preset allowable deformation increment range; The predicted deformation values, the comparison results of deformation increments, and the out-of-limit markers are integrated into a structured output, which is saved in both text table format and binary cloud map format.

[0012] Furthermore, the front support hanging basket includes a main truss system, a front support anchoring system, a rear anchoring system, a traveling system, and a formwork system. In the finite element model, the front support position of the front support hanging basket is connected to the lower edge node of the cast-in-place box girder segment through anchor rod elements. The anchor rod elements are set as rod elements that only bear tensile forces. The rear anchor point is connected to the upper edge node of the cast box girder segment through a fine-rolled threaded steel unit. The fine-rolled threaded steel unit is set as a rod unit that only bears tensile force. During the simulated movement of the hanging basket, the forward movement of the hanging basket is achieved by changing the activation state of the front support anchor bolt unit and the rear anchor fine-rolled threaded steel unit.

[0013] Furthermore, the simulation of segment-by-segment concrete pouring and segment-by-segment prestressing in S5 includes: In the finite element analysis of each construction stage, the concrete pouring process is decomposed into multiple sub-steps, and the gradual change process of concrete from the fluid state to the hardened state is simulated step by step. After the concrete material properties are switched, an analysis step is performed to simulate the concrete curing process. After the maintenance analysis step is completed, activate the longitudinal prestressed steel strand unit in the current segment, and connect the prestressed steel strand unit with the surrounding concrete unit through embedded constraints or common nodes. The prestressing tension simulation adopts the equivalent load method. The equivalent nodal force at both ends of the steel strand is calculated based on the tension control stress. The equivalent nodal force is applied to the end nodes of the steel strand element, and the loss effect is simulated by correcting the value of the equivalent nodal force. After all analysis steps are completed in each construction phase, the structural stiffness matrix, internal force vector, and displacement field of the current phase are completely transferred to the next phase as the initial conditions for the next phase analysis.

[0014] Furthermore, the method also includes: Based on the deformation prediction value of each construction stage, a formwork elevation correction table is generated for the cantilever construction of the front support hanging basket. The formwork elevation correction table includes the segment number of each cantilever segment, the design formwork elevation, the predicted vertical deflection value, and the corrected formwork elevation. The formwork elevation correction table also includes the predicted inter-layer slip of the steel-ECC composite structure area corresponding to each segment, as well as the pre-lifting value of the formwork system suggested based on the predicted inter-layer slip.

[0015] This invention claims protection for a deformation prediction method for cantilever construction using a front-support hanging basket based on finite element simulation, belonging to the field of numerical analysis technology for construction control. It obtains the strength characteristics and ductile deformation properties of engineering cement-based composite materials and constructs a constitutive model of ECC materials. Through experimental research, it studies the static shear performance of short studs in steel-ECC composite structures and analyzes the influence of interlayer bonding. It obtains the local bending performance of the steel-ECC composite structure under positive and negative bending moment loading conditions, establishes bending performance parameters and a finite element model of the cantilever construction process using a front-support hanging basket, inputs constitutive and performance parameters, simulates the movement of the hanging basket, segmental casting, and prestressing tension stage by stage, calculates the deformation at each construction stage, and outputs the predicted deformation values ​​for each stage. This invention can finely consider the nonlinearity of ECC materials, the slippage of the steel-ECC interface, and the time-varying characteristics of the construction process, significantly improving the accuracy of deformation prediction in cantilever construction and providing a reliable basis for formwork elevation adjustment and construction control. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the deformation prediction method for a front-support hanging basket cantilever construction process based on finite element simulation, as claimed in this embodiment of the invention. Figure 2 This is a second flowchart of a deformation prediction method for a front-support hanging basket cantilever construction process based on finite element simulation, as claimed in the embodiments of the present invention. Figure 3 This is the third workflow diagram of a method for predicting deformation during cantilever construction using a front-support hanging basket based on finite element simulation, as claimed in this embodiment of the invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0018] The technical solutions disclosed in the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0019] According to a first embodiment of the present invention, the present invention claims protection for a method for predicting deformation during the cantilever construction process of a front-support hanging basket based on finite element simulation, referring to... Figure 1 This includes the following steps: S1: Obtain the compressive strength, tensile strength, and flexural strength of the engineering cement-based ECC composite material, determine the strength characteristics and ductile deformation properties based on the stress-strain curves obtained from the experiment, and construct the constitutive model of the ECC material; S2: Obtain the static shear performance of short studs in steel-ECC composite structures, measure the shear capacity, shear stiffness and slip capacity of the ejected specimens, analyze the influence of interlaminar bond between steel and ECC on shear performance, and obtain the static shear parameters of short studs; S3: Obtain the local bending performance of the steel-ECC composite structure under positive and negative bending moment loading conditions. Measure the bending capacity, relative slip capacity, and crack resistance of the composite structure under different protective layer thicknesses and reinforcement ratios to obtain the local bending performance parameters under positive and negative bending moment loading conditions. S4: Establish a finite element model of the cantilever construction process of the front support hanging basket, and input the constitutive model of the ECC material, static shear parameters and local bending performance parameters into the finite element model; S5: Simulate the cantilever construction process of the front support hanging basket, including moving the hanging basket segment by segment, pouring concrete segment by segment, and tensioning prestress segment by segment, and calculate the deformation of each construction stage. S6: Output the predicted deformation value of the cantilever construction process of the front support hanging basket based on the deformation amount of each construction stage.

[0020] In this embodiment, a batch of engineering cement-based composite ECC specimens were selected, and prism specimens with dimensions of 70.7mm × 70.7mm × 70.7mm were prepared for the compression test. A total of 6 identical specimens were prepared. Each specimen was placed at the center of the lower platen of the electro-hydraulic servo pressure testing machine, and the upper platen was adjusted to contact the top surface of the specimen. The preload did not exceed 5% of the estimated failure load. A displacement control mode was adopted, and the loading rate was set to 0.05mm / min. Axial pressure was continuously applied until macroscopic cracks appeared in the specimen and it was completely destroyed. The load and axial compression displacement data were recorded throughout the process. The displacement data was divided by the original height of the specimen to convert it into axial compression strain, and the load was divided by the bearing area of ​​5000mm² to convert it into compressive stress. The peak stress was read from the stress-strain curve as the compressive strength, and the strain value when the stress dropped to 80% of the peak stress in the strain softening section was read as the ductility index.

[0021] The direct tensile test used a dog-bone shaped plate specimen with a gauge length of 100 mm and a width of 30 mm in the middle and a clamping width of 60 mm at both ends. Two extensometers with a gauge length of 80 mm were symmetrically attached to both sides of the specimen. The specimen was vertically clamped in the upper and lower clamps of the universal testing machine, with rubber gaskets inside the clamps to avoid stress concentration. Displacement-controlled loading was used at a loading rate of 0.01 mm / min, and the specimen was continuously stretched until it fractured. Load and extensometer readings were collected every 0.1 seconds. The tensile stress was calculated based on the load and the cross-sectional area of ​​the gauge length section of the specimen (30 mm × specimen thickness 12 mm = 360 mm²). The tensile strain was calculated by dividing the extensometer deformation by the gauge length of 80 mm. The slope of the elastic segment was extracted from the tensile stress-strain curve as the elastic modulus, the stress corresponding to the highest point of the curve was extracted as the peak tensile stress, the strain corresponding to the peak tensile stress was extracted as the peak strain, and the strain at failure was extracted as the ultimate tensile strain.

[0022] The four-point bending test used a beam-type specimen with dimensions of 400mm×100mm×15mm and a span of 300mm. The distance between the two loading points was 100mm. The specimen was placed on a four-point bending fixture. The two loading rollers and the two support rollers were all cylindrical with a diameter of 10mm. A linear variable differential transformer was installed at the bottom surface of the mid-span to measure the deflection. Displacement-controlled loading was used with a loading rate of 0.5mm / min. Loading was continued until visible cracks appeared at the bottom of the specimen, and then loading continued until the load dropped to less than 50% of the peak load. Record the load and mid-span deflection data; according to the elastic bending theory, the bending stress = (load × spacing between loading points) / (specimen width × specimen height² / 6), calculate the bending stress under different loads; determine the bending stress corresponding to the first load drop point from the load-deflection curve as the cracking bending strength, and take the bending stress corresponding to the peak load as the bending strength; calculate the area from the origin to the range where the deflection is equal to twice the first cracking deflection under the load-deflection curve, and the area from the origin to the range where the deflection is equal to 5.5 times the first cracking deflection, and the ratio of the two is used as the bending toughness index.

[0023] The compressive strength, compressive strain, and softening data obtained from compression tests, the elastic modulus, peak tensile stress, and ultimate tensile strain obtained from direct tensile tests, and the cracking bending strength, bending strength, and bending toughness index obtained from four-point bending tests are integrated into a single parameter table. Based on these parameters, an ECC material constitutive model is constructed: a three-segment model consisting of a linear elastic segment, a strain hardening segment, and a strain softening segment. The slope of the linear elastic segment is taken as the elastic modulus obtained from the direct tensile test. The starting point of the hardening segment is the elastic limit stress, which is 80% of the peak tensile stress, and the ending point is the point corresponding to the peak tensile stress. The softening segment adopts a linearly decreasing curve, and the ending stress is taken as the strain value corresponding to 30% of the peak tensile stress. This constitutive model is stored in tabular form, with each row containing the strain value and the corresponding stress value for subsequent reading by finite element software.

[0024] A steel-ECC composite ejection specimen was prepared. The steel plate had dimensions of 200mm×200mm×20mm. A short stud with a diameter of 16mm, a height of 80mm, and a head diameter of 25mm was welded to the center of the steel plate.

[0025] The steel plate surfaces were treated in three ways: the first group of steel plate surfaces were coated with epoxy resin adhesive; the second group of steel plate surfaces were cleaned with a wire brush and left to remain in their natural state; the third group of steel plate surfaces were treated with a sandblasting machine to create a rough texture with a roughness Ra of 12.5 μm; ECC material was cast onto the steel plate to form a 100 mm thick ECC plate, with short studs completely embedded; three specimens were prepared for each group, for a total of nine specimens.

[0026] The specimen is mounted on a universal testing machine with the steel plate end-down above the lower pressure plate. Two linear variable differential transformers are symmetrically placed on both sides of the steel plate, with the probes in contact with the bottom surface of the ECC plate to measure the relative slip between the steel plate and the ECC plate. A displacement control method is used, with a loading rate set to 0.5 mm / min, continuously loaded until the specimen fails, the short studs shear off, or the ECC plate splits. Load and displacement readings from the two linear variable differential transformers are collected at a frequency of 5 times per second, and the average of the two displacement readings is taken as the slip.

[0027] Shear capacity is extracted from the load-slip curve, specifically the load value corresponding to the peak point of the curve. Shear stiffness is extracted from the slope of the initial linear segment of the curve from 10% peak load to 40% peak load, calculated by dividing the load increment by the slip increment within this interval. Slip capacity is extracted from the slip value corresponding to the peak load of the curve, as well as the ultimate slip value corresponding to the load decreasing to 85% of the peak load.

[0028] Comparing the load-slip curves of the three groups of specimens, the adhesive-coated group had the largest initial slope and the highest peak load, but the load decreased rapidly after the peak. The rough texture group had a moderate initial slope, a relatively high peak load, and a long plateau segment after the peak. The untreated group had the smallest initial slope and the lowest peak load. The comparison showed that interlayer bonding significantly improved shear capacity; applying the adhesive increased the capacity by approximately 25% and also improved shear stiffness, but the effect on slip capacity was greatest with the untreated group. These patterns were quantified into correction coefficients, such as introducing a bond enhancement coefficient of 1.25 for the finite element input of the capacity and a stiffness correction coefficient of 1.30. The final output corrected static shear parameters included: a baseline shear capacity of 50 kN, a baseline shear stiffness of 200 kN / mm, a baseline slip capacity of 5 mm, and correction coefficients selected based on the interface treatment method.

[0029] Steel-ECC composite beam specimens were prepared. The total beam length was 3000 mm, the steel plate thickness was 10 mm, and the width was 300 mm. Three protective layer thicknesses were used for the ECC layer: 50 mm, 70 mm, and 90 mm. The protective layer refers to the distance from the top surface of the steel plate to the center of the longitudinal reinforcement. The longitudinal reinforcement used 12 mm diameter HRB400 steel bars with reinforcement ratios of 0.5%, 1.0%, and 1.5%, respectively. The reinforcement bars were placed within the ECC layer at a distance of one protective layer thickness from the top surface of the steel plate. Three specimens were prepared for each combination of protective layer thickness and reinforcement ratio, for a total of 27 specimens.

[0030] The composite beam specimen was simply supported at both ends on two supports with a support spacing of 2250 mm, which is three-quarters of the beam length. Two loading points were set in the mid-span region with a spacing of 750 mm, which is one-third of the support spacing. A distribution beam was placed above the loading points, and the distribution beam was in contact with the pressure head of the testing machine. Three linear variable differential transformers were installed on the bottom surface of the mid-span and the bottom surface of the two loading points for measuring deflection. A sliding measurement section was set every 500 mm along the beam length, and two dial gauges were symmetrically installed on each section. The gauge bases were fixed to the side of the steel plate, and the probes were in contact with the side of the ECC layer.

[0031] Displacement-controlled loading was used, with a loading rate of 1 mm / min, and loading continued until the specimen completely failed and the load dropped to less than 50% of the peak load. Throughout the process, load values, deflection values, and slip values ​​were collected every 0.5 seconds. At the same time, a crack observation instrument with a magnification of 20x and a flashlight were used to observe the surface of the ECC layer. The load when the first visible crack appeared was recorded. When a new crack appeared, its location and width were recorded, and the width value was measured using a crack width measuring card. The width change of existing cracks was measured every time the load increased by 10 kN.

[0032] The composite beam specimen is fixed at both ends to specially designed fixed supports, which provide completely fixed rotational constraints. A vertical load is applied at mid-span using the same loading device as for the positive bending moment, at which point the top ECC of the beam is under tension and the bottom steel plate is under compression. Alternatively, an inverted simply supported method is used, where the specimen is rotated 180 degrees and tested under the support and loading conditions of the positive bending moment condition. The data acquisition method for the negative bending moment condition is the same as that for the positive bending moment condition.

[0033] The load at the first crack appearance is extracted from the load-mid-span deflection curve as the crack initiation load value, the load at the peak of the curve is taken as the peak load value, and the load at which the deflection reaches four times the peak deflection after the peak load is taken as the residual load value. The flexural bearing capacity is a combination of these three values. The slip value with the largest absolute value measured at each section is selected as the relative slip capacity of the specimen. The slip distribution curve along the beam length is plotted, with the horizontal axis representing the section position and the vertical axis representing the slip amount.

[0034] A three-dimensional geometric model of the cantilever construction process using finite element preprocessing software was established. The main truss system of the cantilever formwork was drawn according to the design drawings. The main truss consists of two main longitudinal beams and a transverse connecting system. The cross-sectional dimensions of each member were input according to the drawings. The geometry of the concrete box girder of block 0 and cantilever segments 1 to N was drawn according to the bridge construction drawings. The top plate of the box girder is 15m wide, the bottom plate is 8m wide, and the web thickness is 0.5m. All steel-ECC composite structure areas were marked in the geometric model. These areas are located within 3m of the ends of each segment.

[0035] The main truss members of the hanging basket adopt B31 beam elements with an element length of 0.2m; the front support anchor rods and rear anchor rods with precision rolled threaded steel adopt T3D2 bar elements, with each anchor rod divided into 2 elements; the traveling track adopts S4R shell elements with an element size of 0.1m; the concrete box girder segments adopt C3D8R solid elements with an element size of 0.2m; the steel plates in the steel-ECC composite structure area adopt S4R shell elements with an element size of 0.05m, the ECC layer adopts C3D8R solid elements with an element size of 0.05m, and the short studs adopt SPRING2 spring elements, with each stud represented by a spring element. The two nodes of the spring element are connected to the steel plate shell element node and the ECC solid element node, respectively.

[0036] A contact pair is established on the contact surface between the steel shell element and the ECC solid element. The principal surface of the contact pair is selected from the outer surface of the steel shell element, and the secondary surface is selected from the corresponding surface of the ECC solid element. In the contact properties, the normal behavior is set to hard contact, allowing separation after contact. The tangential behavior is set to penalty friction, with a friction coefficient of 0.4. The static shear parameters obtained from the push-out test are converted into the stiffness properties of the spring element. Each spring element is assigned a nonlinear spring property, which defines the relationship between relative displacement and spring force in tabular form. The tabular data comes from the load-slip curve of the push-out test. At the same time, the modified bond-slip constitutive curve is used as a supplementary definition of the tangential behavior of the contact pair, allowing slip when the tangential stress exceeds the critical value.

[0037] The constitutive model of the ECC material constructed in S1 is assigned to the solid elements of the ECC layer by means of user material subroutines or by directly inputting stress-strain data tables; the bilinear elastoplastic constitutive model of steel is assigned to the steel plate shell elements and steel bar elements, with a yield strength of 345 MPa, an elastic modulus of 206 GPa, and a hardening modulus of 2.06 GPa.

[0038] Fixed constraints are applied to the end face of the zero block segment that has been poured, constraining all six degrees of freedom of the nodes; vertical and longitudinal fixed constraints are applied at the anchor point of the hanging basket, allowing slight lateral movement; rolling support constraints are set at the support point of the hanging basket, constraining vertical and longitudinal displacement but allowing rotation about the lateral axis.

[0039] A sequence of analysis steps is established in the finite element solver, with one set of analysis steps corresponding to each construction stage. Taking the pouring of segment 3 in construction stage 3 as an example: Step 1: Move the hanging basket model from the previous segment 2 position to the current segment 3 position; the movement operation is achieved by writing a node coordinate update script to read the node number of all elements of the hanging basket, increase its x-coordinate bridge longitudinally by one segment length of 4m, regenerate the element connection relationship, and retain the original element type and attributes.

[0040] Step 2: Activate the concrete box girder solid elements and steel bar elements of segment 3 by modifying the element state parameters from passivated to active; at the same time, activate the longitudinal prestressed duct elements and prestressed steel strand elements inside this segment, with the duct elements being solid elements and the steel strand elements being bar elements.

[0041] Step 3: Apply load; apply a gravitational acceleration of 9.8 m / s² and a material density of 2500 kg / m³ to all solid units, and the program will automatically calculate the self-weight load; apply a construction live load to the hanging basket formwork system, with the value set at a uniformly distributed load of 2.5 kN / m² applied to the formwork surface.

[0042] Step 4: Perform finite element analysis; use the Newton-Raphson incremental iterative solver, set the initial increment step size to 0.1, the minimum increment step size to 1e-6, and the maximum increment step size to 100; after the solution is completed, extract the vertical displacements of the upper and lower edges of the front section of the current segment from the results.

[0043] Step 5: Perform prestressing tension simulation; use the equivalent load method for the prestressed steel strand element to calculate the equivalent nodal force at both ends of the steel strand when the tension control stress is 1395MPa. The magnitude of the force is equal to the cross-sectional area of ​​the steel strand multiplied by the control stress. Apply this equivalent nodal force as a concentrated load to the nodes at both ends of the steel strand. Consider the friction loss of the prestressing ducts, with a friction coefficient of 0.25, and correct the equivalent nodal force after calculating the loss based on the steel strand rotation length. Execute the solution again to obtain the vertical displacement increment after tensioning. Superimpose the displacement value before tensioning with the increment value to obtain the final deformation amount for this stage.

[0044] Step 6: Save the displacement and stress values ​​of all nodes in the current stage as the initial state file for the next stage. Change the state of the hanging basket element to passivation.

[0045] Repeat the above steps until all cantilevered segments have been simulated.

[0046] After each construction stage is solved, the post-processing script is automatically run. The script extracts the deformation by node set: the node set at the front support point of the hanging basket has 4 nodes, the node set at the upper edge of the front section of the current segment is equidistant along the transverse direction with 5 nodes, and the node set at the lower edge also has 5 nodes, the node at the mid-span closure position of the completed segment is selected at the center of the closure segment, the node set at the rear anchor point of the hanging basket has 2 nodes, and the node pair set on the interface between the steel plate and ECC in the steel-ECC composite structure area contains one steel plate node and the nearest ECC node.

[0047] Calculate the deformation value of each node. The vertical displacement is the change in the node's Z coordinate, and the horizontal displacement is the change in the node's X coordinate. Write the deformation of each construction stage into a table file in the order of the stages. The table header includes: stage number, node name, node coordinate, vertical displacement, horizontal displacement, and total displacement.

[0048] Calculate the predicted vertical deflection of the front section of the current segment: take the average value of the vertical displacement of the 5 nodes at the upper edge and the average value of the vertical displacement of the 5 nodes at the lower edge, and then take the arithmetic mean of these two average values ​​as the final predicted vertical deflection value. The predicted horizontal displacement value is the displacement value of the center node of the front section along the X-axis.

[0049] Calculate the elastic deformation of the nodes at the front support point of the hanging basket: extract the displacement of the front support node under gravity load and construction live load and subtract the initial displacement. Calculate the axial deformation of each member of the main truss of the hanging basket: extract the component of the displacement difference between the two ends of each member along the axis of the member, and output the elastic deformation of the front support point and the axial deformation of each member to the same table.

[0050] Linear superposition of deformations under different load conditions: In the analysis of the same construction stage, the displacement fields when only gravity load is applied, the displacement fields when only live load is applied, the displacement fields when only prestress load is applied, and the displacement fields when only the self-weight of the hanging basket are considered are output respectively. Then, the nodal displacement values ​​of these four displacement fields are directly added together to obtain the total displacement field.

[0051] For the steel-ECC composite structure region, the relative displacement vector between each node pair is extracted by subtracting the displacement of the ECC node from the displacement of the steel plate node. The magnitude of the component of this vector in the tangent plane on the steel plate surface is calculated as the predicted value of inter-story slip. A cross section is taken every 0.1m along the beam length from the start to the end of the composite structure to draw the slip distribution curve. The abscissa and ordinate data of the curve are output as a text file.

[0052] Output a deformation prediction result file. The filename includes the construction number and date. The file format is .csv text, containing a list of deformation values ​​for all key nodes in each construction stage. Simultaneously, output deformation contour map data as a binary file (.vtk) for visualization software to read. For each construction stage, calculate the difference in deformation between each node in the current stage and the previous stage to obtain a deformation increment sequence. The preset allowable range for deformation increments is: a maximum allowable vertical deflection increment of 15mm and a maximum allowable horizontal displacement increment of 5mm. For increments exceeding the allowable range, add an over-limit marker line to the end of the output file, with the marker content as: Stage X, Node Y, Vertical Increment XXmm, Over-limit +XXmm. Finally, integrate the deformation prediction value table, deformation increment comparison table, and over-limit markers into a single Excel file, and output a binary file of the deformation contour map.

[0053] Furthermore, in S1, a prism specimen is used, and axial pressure is applied until the specimen fails. The peak load and the corresponding axial compressive strain are recorded, and the compressive strength is calculated based on the ratio of the peak load to the bearing area of ​​the specimen. A dog-bone shaped plate specimen was used. Axial tension was applied to both ends of the specimen, and tensile strain within the gauge length was measured using an extensometer to obtain the full curve of tensile stress versus tensile strain. The elastic modulus, peak tensile stress, and ultimate tensile strain were extracted from the full curve as parameters for tensile strength characteristics and ductile deformation properties. A beam-type specimen was used, and two symmetrical loads were applied to the mid-span region at the bottom of the specimen. The relationship curve between the load and the mid-span deflection was measured. The bending strength and bending toughness index were calculated according to the bending stress formula. The bending toughness index was determined by the ratio of the area under the load-deflection curve to the area corresponding to the first cracking load.

[0054] In this embodiment, six prism-shaped ECC specimens measuring 70.7mm × 70.7mm × 70.7mm were prepared and cured in a standard curing room at 20±2℃ and a relative humidity of over 95% for 28 days before being removed. The surfaces of the specimens were cleaned with compressed air, and the actual dimensions of each specimen were measured to an accuracy of 0.01mm. The electro-hydraulic servo pressure testing machine was preheated for 30 minutes, and a 100mm diameter spherical indenter was installed. The upper pressure plate was adjusted using an automatic leveling method. The specimen was placed in the center of the lower pressure plate, ensuring that the specimen axis coincided with the axis of the indenter. The loading rate control mode was set to displacement control at a rate of 0.05mm / min. Loading was initiated, and the testing machine control system recorded the load and displacement values ​​every 0.1 seconds. The test was stopped when the load reached its peak and then decreased to 70% of the peak load. After saving the data, the compressive stress was obtained by dividing the load by the actual measured length × width of the bearing area, and the compressive strain was obtained by dividing the displacement by the specimen height. Outliers with a dispersion exceeding ±15% of the average value were removed from the results of the 6 specimens, and the average value of the remaining specimens was taken as the final compressive strength and compressive strain data. At the same time, the failure mode of each specimen was recorded: whether a through-crack appeared, whether spalling occurred, and whether the integrity was maintained.

[0055] Dog-bone shaped flat specimens were prepared using molds made according to ASTM C1579 standards. The total length of the specimen was 230 mm, with a 100 mm long and 30 mm wide gauge length section in the middle, and 65 mm long and 60 mm wide clamping sections at both ends. The transition radius was 25 mm, and the thickness was uniformly 12 mm. Five specimens were prepared for each mix proportion. After curing for 28 days, two iron plates were glued to both sides of the gauge length section of the specimen with epoxy resin. The extensometer blades were embedded in the grooves of the iron plates, and the extensometer gauge length was 80 mm. The specimens were clamped at both ends in the hydraulic clamps of a universal testing machine with a clamping pressure set to 3 MPa to prevent slippage. A displacement control mode was used with a loading rate of 0.01 mm / min. The data acquisition system records the load and the deformation values ​​of the two extensometers every 0.2 seconds. The average of the two extensometer readings is taken as the gauge length deformation. During the loading process, a camera records the evolution of surface cracks on the specimen. The test is stopped when the load drops to 30% of the peak load. For data processing, the load is divided by the cross-sectional area of ​​the gauge length (30mm × 12mm = 360mm²) to obtain the tensile stress, and the extensometer deformation is divided by 80mm to obtain the tensile strain. On the stress-strain curve, the slope of the straight line segment from zero stress to the point where the elastic limit stress is 80% of the peak stress is taken as the elastic modulus. The highest stress value on the curve is taken as the peak tensile stress, and the strain corresponding to this point is taken as the peak strain. The strain at the fracture point is taken as the ultimate tensile strain. If the specimen fractures outside the gauge length, the data for that specimen is invalid.

[0056] Beam-shaped specimens with dimensions of 400mm×100mm×15mm were prepared. Aluminum alloy templates were used in the molds to ensure flatness. Six specimens were prepared for each mix design. After curing for 28 days, the specimens were placed on a four-point bending fixture. The fixture support span was 300 mm, the distance between the two loading points was 100 mm, and the diameter of the loading roller and support roller was 10 mm. The roller surface was wrapped with rubber pads to reduce local indentation. An LVDT iron plate was attached to the bottom surface of the specimen at mid-span using quick-drying adhesive. The LVDT sensor was fixed on an independent bracket with a range of ±10 mm. The loading test machine was turned on, using displacement control mode and a loading rate of 0.5 mm / min. The data acquisition system recorded the load and mid-span deflection every 0.1 seconds. At the same time, a digital image correlation (DIC) system was used to capture side images of the specimen every 2 seconds for subsequent analysis of crack width and distribution. The test was stopped when the load dropped to 50% of the peak load. During data processing, the first point of slope change on the load-deflection curve where the load suddenly dropped or the slope decreased was identified as the cracking load. The cracking load was determined according to the bending stress formula σ = Calculate the cracking flexural strength using (P×a) / (b×h² / 6), where P is the cracking load, a is the spacing between loading points (100mm), b is the specimen width (100mm), and h is the specimen height (15mm). Calculate the flexural strength based on the load corresponding to the peak point of the curve. Calculate the flexural toughness index: First, determine the deflection value of the cracking load corresponding to the initial cracking deflection δ_c. Calculate the area A_c under the load-deflection curve from 0 to δ_c, then calculate the area A_total from 0 to 5.5δ_c. The toughness index I5 = A_total / A_c. Output the average and standard deviation of the 6 specimens.

[0057] Furthermore, referring to Figure 2 S2 includes the following operations: Prepare a steel-ECC composite specimen by welding short studs to the upper surface of the steel plate and casting ECC material on top of the steel plate to form an ECC plate, so that the short studs are completely embedded in the ECC plate; The ejected specimen was installed in a universal testing machine. A vertical ejection load was applied to the end of the steel plate. Two linear variable differential transformers were symmetrically arranged on both sides of the specimen to measure the relative slip between the steel plate and the ECC plate. Continuous loading was performed using displacement control, and the load-slip curves were recorded throughout the entire process. Shear capacity is extracted from the load-slip curve as the peak load value of the curve, shear stiffness is extracted as the slope value of the straight part of the rising segment of the curve, and slip capacity is extracted as the slip amount corresponding to the peak load and the ultimate slip amount. By preparing multiple sets of ejection specimens with different interface treatments, comparing the differences in load-slip curves among the specimens, analyzing the influence of interlaminar bonding on shear capacity, shear stiffness, and slippage capacity, and obtaining modified static shear parameters considering the interlaminar bonding effect.

[0058] In this embodiment, nine Q345 steel plates, each measuring 200mm × 200mm × 20mm, are processed. A 16.5mm diameter hole with a depth of 15mm is drilled in the center of each plate. A short stud with a diameter of 16mm, a height of 80mm, a head diameter of 25mm, and a head thickness of 5mm is inserted into the hole. The stud is welded from the back of the steel plate using carbon dioxide gas shielded welding with a welding current of 180A and an arc voltage of 22V, ensuring root penetration and a weld leg height of not less than 6mm. After welding, the slag is cleaned, and the stud perpendicularity is measured. Specimens with a deviation exceeding 2 degrees are discarded.

[0059] Nine specimens were divided into three groups of three. Group 1: Epoxy resin adhesive was evenly applied to the side of the steel plate with the welded studs, with a thickness of 0.3 mm. The coating was smoothed with a notched scraper and cured at room temperature for 24 hours. Group 2: The surface of the steel plate was repeatedly brushed 20 times in the same direction with a wire brush to remove loose rust. After cleaning with compressed air, the plate was allowed to dry naturally. Group 3: The surface of the steel plate was sandblasted using a sandblasting machine. The sandblasting medium was quartz sand with a particle size of 0.5-1.0 mm. The spraying angle was 75° and the sandblasting distance was 150 mm. The surface roughness was treated until it reached Ra12.5 μm, and then calibrated using a roughness comparison sample.

[0060] Cast ECC material and construct a wooden mold with an inner cavity size of 200mm × 200mm × 110mm. Place a steel plate at the bottom of the mold with the studs facing upwards, and seal the perimeter of the steel plate with sealing strips to prevent grout leakage. Mix the ECC material according to the following mass ratio: 1 part cement, 1.2 parts fly ash, 0.8 parts quartz sand, 2% polyvinyl alcohol fiber by volume, and a water-cement ratio of 0.28. Pour the mixture into the mold, compact it with a vibrating table for 1 minute, and then smooth the surface with a scraper. Cure in a standard curing room for 24 hours, then remove the mold and continue curing for 28 days. During the curing period, cover the top surface of the ECC board with a damp cloth to keep it moist.

[0061] Remove the cured specimen from the curing chamber and wipe off any surface moisture. Place the specimen on the lower pressure plate of the universal testing machine, ensuring the bottom of the steel plate is in full contact with the pressure plate and the center of the specimen is aligned with the center of the testing machine's indenter. Place two linear variable differential transformers (LVDTs) symmetrically on the left and right sides of the specimen. The LVDT probes are fitted with magnetic bases at their ends, which are attached to the testing machine's column. The probes contact the edge of the ECC plate's bottom surface, with a preload of 1 mm to ensure good contact. The LVDT's range is ±10 mm, and its accuracy is 0.001 mm. Place a 10 mm high pad under each of the four corners of the steel plate's bottom surface to create a gap between the steel plate's bottom surface and the lower pressure plate, preventing obstruction of relative sliding.

[0062] The signal lines of the two LVDTs are connected to the first and second channels of the data acquisition instrument, and the load sensor signal of the testing machine is connected to the third channel; the sampling frequency is set to 10Hz, that is, 10 data are collected per second; the data acquisition instrument is connected to the computer, and the load-slip curve is displayed in real time using the accompanying software.

[0063] Start the testing machine and lower the indenter to approximately 2 mm from the top of the specimen. Set the testing machine control mode to displacement control and the loading rate to 0.5 mm / min. Begin loading and simultaneously start the data acquisition software to record data. Observe the changes in the load value during loading. When the load shows a significant decrease of more than 5%, continue loading until the load drops to 85% of the peak load. Then, add another 10 mm of slippage and stop the test. If the specimen suddenly fails, such as with a popping sound like a stud shearing, immediately stop the test and record the failure mode.

[0064] Throughout the test, the ECC plate surface was visually inspected every 2 minutes for cracks, and the direction of the cracks was marked with a marker. The failure phenomena of each specimen were recorded: whether the studs were sheared, whether the ECC plate was split, and whether the interface between the steel plate and the ECC plate was separated.

[0065] Export the original load-slip data, and take the arithmetic mean of the slip values ​​of the two LVDTs as the slip amount at that moment; for each group of 3 specimens, plot the load-slip curves respectively.

[0066] Extracting shear capacity from the curve: Find the maximum value of the curve. If the maximum value has a clear plateau, take the load value at the starting point of the plateau. Extract shear stiffness: Select data points P_u between 0.2P_u and 0.4P_u in the rising segment of the curve as the shear capacity. Perform linear fitting on these points. The slope of the fitted line is the shear stiffness. Extract slip capacity: The slip corresponding to the peak load is denoted as s_u, and the slip corresponding to the load decreasing to 0.85P_u is denoted as s_0.85. Take the two values ​​of s_u and s_0.85.

[0067] The parameters of the three groups of specimens were compared: the average shear capacity of the first group with adhesive coating was denoted as P_b1, the second group without treatment was denoted as P_b2, and the third group with rough texture was denoted as P_b3. The bond reinforcement coefficient k_bond = P_b1 / P_b2 and the rough texture reinforcement coefficient k_rough = P_b3 / P_b2 were calculated. The shear stiffness reinforcement coefficient was calculated using the same method. The baseline values ​​for the untreated group and the correction coefficients were compiled into a table and output as a short stud static shear parameter file.txt. The file content includes: baseline shear capacity (kN), baseline shear stiffness (kN / mm), baseline slip capacity (mm), and the coefficients corresponding to the two reinforcement methods. This parameter file is used by the spring elements and contact properties in the finite element model.

[0068] Further, S3 includes: Steel-ECC composite beam specimens were prepared, with multiple different values ​​for protective layer thickness and multiple different values ​​for reinforcement ratio; For positive bending moment loading, the composite beam specimen is simply supported on two supports, and vertical loads are applied at two symmetrical points in the mid-span region of the beam, so that the bottom steel plate of the beam is under tension and the top ECC is under compression. For negative bending moment loading, the two ends of the composite beam specimen are constrained by fixed supports, and vertical loads are applied at two symmetrical points in the mid-span region of the beam, so that the top ECC of the beam is under tension and the bottom steel plate is under compression. Alternatively, the original positive bending moment specimen can be flipped over and loaded using an inverted simply supported method. Displacement control mode was used during both positive and negative bending moment loading processes. The loading rate was controlled to keep the rate of increase of mid-span deflection constant. The load values ​​of the load sensor, the deflection values ​​of the linear variable differential transformer arranged at mid-span, the relative slip of the slip measurement points arranged on multiple sections along the beam length, and the development of surface cracks in the ECC layer were continuously recorded. The flexural bearing capacity is determined based on the recorded load-mid-span deflection curve. The flexural bearing capacity includes the cracking load value when the first crack appears, the peak load value on the curve, and the residual load value corresponding to a specific deflection-ductility ratio after the peak load. Based on the relative slip measured at multiple cross sections, a slip distribution curve along the beam length is plotted, and the maximum slip is extracted from the distribution curve as the relative slip capacity of the specimen. During the loading process, the load value at which the first visible crack appeared on the surface of the ECC layer was recorded using a magnifying glass and a crack observation instrument as the crack initiation load. The average and maximum values ​​of the crack spacing were measured, and the rate of change of the crack width with the increase of the load was measured to obtain crack resistance indicators including crack initiation load, crack spacing range, and crack width growth rate. The flexural bearing capacity, relative slip capacity, and crack resistance obtained under all positive bending moment conditions are summarized as local flexural performance parameters under positive bending moment conditions, and the corresponding indices obtained under all negative bending moment conditions are summarized as local flexural performance parameters under negative bending moment conditions.

[0069] In this embodiment, a composite beam specimen was prepared at a 1:4 scale based on the actual structural dimensions of the bridge. The total beam length was 3000mm, and the steel plate was made of Q345 steel with a thickness of 10mm, a width of 300mm, and a length of 3000mm. Vertical ribs were welded to both sides along the length of the steel plate, with a height of 20mm, a thickness of 8mm, and a spacing of 300mm, to prevent local buckling of the steel plate. An ECC layer was cast on top of the steel plate, and the protective layer thickness was 50mm, 70mm, and 9mm from the top surface of the steel plate to the center of the reinforcing bar, respectively. 0mm; Longitudinal reinforcement uses 12mm diameter HRB400 steel bars, with reinforcement ratios of 0.5%, 1.0%, and 1.5%, corresponding to 2, 4, and 6 steel bars evenly spaced within the ECC layer; The distance from the top surface of the steel bar to the top surface of the ECC is uniformly 25mm; A 6mm diameter U-shaped anchor head is welded to both ends of each steel bar, extending into the support area to enhance anchorage; Three specimens are prepared for each combination of cover thickness and reinforcement ratio, for a total of 27 specimens. Specimen numbering method: The first segment of numbers indicates the cover thickness 50 / 70 / 90mm, the second segment indicates the reinforcement ratio 0.5 / 1.0 / 1.5%, and the third segment indicates the serial number of the repeating specimen 1 / 2 / 3. For example, 50-1.0-2 indicates the second specimen with a cover thickness of 50mm and a reinforcement ratio of 1.0%.

[0070] After the specimens were cast, they were cured for 28 days. During the curing period, the ECC surface was covered with wet burlap sacks and watered twice a day. After the curing period, white matte paint was sprayed on both ends of the specimen within 500 mm to mark the cracks.

[0071] The specimen was hoisted onto the four-point bending test platform. Two supports were installed, each consisting of a cylindrical roller with a diameter of 50 mm and a length of 320 mm. The rollers were placed on a steel base, which was fixed to the test platform. The center-to-center distance between the two supports was 2250 mm, and the specimen extended 375 mm from each end. Two loading rollers, each with a diameter of 50 mm and a length of 320 mm, were installed above the two supports, with a center-to-center distance of 750 mm. A distribution beam, an I-beam with a length of 1000 mm, was placed above the loading rollers, with its center directly facing the pressure head of the testing machine.

[0072] Iron plates were attached to the bottom surface at mid-span and directly below the two loading points of the specimen, and three LVDTs with a range of ±50mm were installed. The LVDTs were fixed on magnetic supports, which were placed on independent foundations on the ground and did not contact the test platform. A sliding measurement section was set every 500mm along the beam length, with the section positions located at 500mm, 1000mm, 1500mm mid-span, 2000mm, and 2500mm from the beam end, respectively. Two dial indicators were symmetrically installed on each section, with the base of the dial indicator attached to the side of the steel plate by a strong magnet. The dial indicator probes were horizontally pressed against the side of the ECC layer with a preload of 1mm.

[0073] The testing machine was started in displacement control mode, with the loading rate set to 1 mm / min. Simultaneously, the data acquisition system was activated, recording the load, LVDT deflection, and dial gauge slip values ​​twice per second. Two testers stood on either side of the specimen, using a handheld crack observation instrument with 20x magnification and illumination to observe the ECC layer surface. Upon discovering the first visible crack, the event marker button was immediately pressed, and the load value at that moment was recorded as the cracking load. The distance from the crack location to the beam end and the initial width were measured using a crack width measuring card with an accuracy of 0.02 mm. Thereafter, for every 10 kN increase in load, loading was paused for 30 seconds, and the width and location of all visible cracks were measured. When the load reached its peak and began to decrease, loading continued until the load dropped to 50% of the peak load or the mid-span deflection reached 100 mm, at which point loading was stopped.

[0074] After unloading, trace the crack with a marker and mark the width at both ends of the crack; measure the distance between adjacent cracks with a steel ruler and record the minimum distance, maximum distance and average distance.

[0075] Negative bending moment loading employs a fixed support method. The specimen is placed on two fixed supports at both ends, each consisting of two steel plates. The lower plate is fixed to the test platform, and the upper plate is tightened to the specimen ends with four bolts of 200 N·m to restrict rotation and vertical displacement. The loading device is the same as for positive bending moment: two loading rollers with a center-to-center distance of 750 mm are applied, resulting in tension on the ECC at the top of the beam. For the inverted simply supported method, the specimen is rotated 180 degrees so that the steel plate faces upwards and the ECC faces downwards. The supports and loading device are then installed according to the simply supported conditions for positive bending moment. The actual stress pattern is equivalent to that of negative bending moment. In the inverted method, the ECC layer is located in the bottom tension zone, and the same data acquisition method as for the positive bending moment specimen applies. Other measurement arrangements for the negative bending moment condition, such as the LVDT, dial gauge, and crack observation, are exactly the same as for the positive bending moment, with consistent data acquisition frequency and recording content.

[0076] The following parameters were extracted from the data collected from each specimen: Bending capacity: The load corresponding to the first point of slope decrease on the load-mid-span deflection curve is taken as the cracking load value; the load corresponding to the highest point of the curve is taken as the peak load value; the load corresponding to the deflection reaching 4 times the peak deflection after the peak load is taken as the residual load value.

[0077] Relative slip capacity: For each slip measurement section, take the larger absolute value of the two dial gauge readings on the left and right sides of the section as the slip amount of that section; find the maximum value of the slip amount among all sections, and take it as the relative slip capacity of the specimen; plot the slip amount of each section with the section position, and draw the slip distribution curve along the beam length, with the horizontal axis being the distance from the beam end and the vertical axis being the slip amount.

[0078] Crack resistance index: Crack load N / mm², divided by specimen width and effective cross-sectional height to be converted into stress; Crack spacing range: minimum spacing, maximum spacing; Crack width growth rate: Select the three cracks with the largest width, plot the width as a function of load for each crack, calculate the load increment during the crack width increase from 0.05mm to 0.5mm, divide by this increment to obtain the growth rate, in mm / kN, and take the average value of the three cracks.

[0079] The parameters of the above-mentioned specimens under all positive bending moment conditions were grouped and summarized according to the protective layer thickness and reinforcement ratio to form a local bending performance parameter table for positive bending moment. The table includes the average value and standard deviation of cracking load, peak load, residual load, maximum slip, average crack spacing, and crack width growth rate for each group. Similarly, the negative bending moment data were processed to obtain a negative bending moment parameter table. Both tables were saved as Excel files, named positive_moment_parameters.xlsx and negative_moment_parameters.xlsx, respectively.

[0080] Furthermore, referring to Figure 3 S4 includes: A three-dimensional geometric model was established based on the structural design drawings of the front support hanging basket and the construction drawings of the bridge cantilever segment; The main truss members of the hanging basket are meshed using beam elements, the front support anchor rods and rear anchor threaded steel bars are meshed using rod elements, the traveling track is meshed using shell elements, the concrete box girder segments are meshed using solid elements, and the steel plates in the steel-ECC composite structure area are meshed using shell elements, the ECC layer is meshed using solid elements, and the short studs are meshed using spring elements. A contact pair is established on the contact surface between the steel plate element and the solid element of the ECC layer. The normal behavior of the contact pair is defined as hard contact, and the tangential behavior is defined as penalty friction. The static shear parameters obtained from the push-out test are converted into the stiffness properties of the spring element or the bond slip constitutive curve of the contact pair. The constitutive model of ECC material is assigned to the solid elements of ECC layer, and the bilinear elastoplastic constitutive model of steel is assigned to the steel plate shell elements and steel bar elements. Displacement constraints are applied at the boundaries of the model, including fixed-end constraints at the ends of the zero block segments that have been poured, vertical and longitudinal fixed constraints at the anchor points of the hanging basket, and rolling support constraints that allow only vertical movement at the front support points of the hanging basket.

[0081] In this embodiment, the geometric parameters of the main truss system of the hanging basket are extracted from the design drawings: the main truss adopts a double-piece triangular truss, and each piece of truss consists of a main longitudinal beam of HN400×200 steel with a length of 12m, a front diagonal brace of HN300×150 steel with a length of 6.5m, a rear diagonal brace of HN300×150 steel with a length of 5.8m, and a vertical bar of HW200×200 steel with a length of 2.8m; a transverse connection system is set between the two trusses, using I20a I-beams; the front support anchoring device includes two anchor rods of 32mm diameter precision-rolled threaded steel with a length of 3.5m and an anchoring seat; the rear anchoring system includes four precision-rolled threaded steels of 32mm diameter with a length of 4m and a spreader beam; the traveling track uses I28a I-beams with a length of 8m, and there are two tracks in total; the formwork system includes the bottom formwork platform of I25a I-beams with longitudinal and transverse beams, the side formwork steel plate with a thickness of 8mm, and the inner formwork combined steel formwork.

[0082] Geometric parameters of the cantilevered segments were extracted from the bridge construction drawings: segment 0 is 12m long, segments 1 to 10 are each 4m long, the top slab thickness is 0.28m, the bottom slab thickness gradually decreases from 0.5m to 0.3m, and the web thickness is 0.5m. The steel-ECC composite structure area is located within 3m of the end of each segment. In this area, an 8mm thick steel plate is laid on the bottom slab, and an ECC layer is poured on top of the steel plate, with longitudinal reinforcement arranged within the ECC layer.

[0083] Using the geometric modeling module of the finite element preprocessing software, parts were created in a top-down manner. First, wireframe models of each member of the hanging basket were created, and then section properties were assigned to generate solids. Box girder segments were created using extrusion and lofting methods. First, a section sketch was created, and then the solid was obtained by extruding along the bridge direction. Each segment was saved as an independent part so that they could be activated one by one in the simulation.

[0084] The main truss members of the hanging basket are: B31 beam elements, two-node three-dimensional beam elements, with a unit length of 0.2m. Each member is equally divided along the axial direction, and elements are generated at the node positions. The front support anchor and the rear anchor threaded steel are: T3D2 bar elements, two-node three-dimensional truss elements. Each anchor is divided into 2 elements with unit lengths of 1.75m and 1.75m respectively. The traveling track is: S4R shell elements, four-node reduced integral shell elements, with a unit size of 0.1m. It is divided into 4 elements along the width direction of the track and one element every 0.1m along the length direction.

[0085] Concrete box girder segments: C3D8R solid elements with eight nodes and hexahedral linear reduced integral elements are used, with an element size of 0.2m. For thickness direction division: the top plate is divided into 2 layers of elements, the bottom plate into 3 layers, and the web into 2 layers. For the steel-ECC composite structure area: the steel plate uses S4R shell elements with an element size of 0.05m, one element every 0.05m along both the plate length and width directions; the ECC layer uses C3D8R solid elements with an element size of 0.05m, one element every 0.01m along the thickness direction. If the ECC layer is 50mm thick, it is divided into 5 layers. Short studs use SPRING2 spring elements with two nodes, each stud represented by one spring element. The starting node of the spring element is the node on the steel plate shell element that coincides with the stud position, and the ending node is the node in the ECC solid element closest to the stud position.

[0086] After the mesh is generated, check the element quality: the aspect ratio should not exceed 3, the warpage should not exceed 5°, and the minimum Jacobian matrix should be greater than 0.5; for elements that do not meet the quality requirements, manually re-mesh them.

[0087] Assign the stress-strain data table of the ECC material constitutive model obtained in S1 to the solid elements of the ECC layer.

[0088] Specific steps: In the material module of the finite element software, create a material named ECC, select the isotropic elastic option and input the elastic modulus obtained from the tensile test, select the concrete damage plasticity or user-defined field option, and import the stress-strain data table in the sub-options; the first column of the data table is the strain value from 0 to the ultimate strain, and the second column is the corresponding stress value from 0 to the peak stress and then down to the residual stress.

[0089] Bilinear elastoplastic constitutive model of steel: Create material STEEL with density 7850kg / m³, elastic modulus 206GPa, Poisson's ratio 0.3, yield stress 345MPa, and plastic stage hardening modulus 2.06GPa, i.e. the slope of the stress-strain curve after yielding is 0.6% of the yield stress; assign this material to steel plate shell elements, steel bar elements, main truss members of hanging basket elements, and traveling track elements.

[0090] The static shear parameters obtained from the push-out test are converted into stiffness properties of the spring elements: A spring element section property is created, typed as connector-axial, defining a force-displacement nonlinear relationship; in the spring property table, displacement values ​​of 0mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, and 8mm are entered, along with the corresponding force values ​​obtained by interpolation from the push-out test load-slip curve. This spring property is then assigned to all SPRING2 elements representing the studs.

[0091] On the far end face of segment 0, select all nodes and apply displacement constraints: U1=0 longitudinal, U2=0 transverse, U3=0 vertical, UR1=0, UR2=0, UR3=0; at each rear anchor point of the hanging basket, select the node at that point and apply constraints of U1=0 and U3=0, allowing small displacements in the U2 direction. In actual simulation, the spring stiffness is approximated as 1e6N / mm; at the node where the front support anchor rod connects to the cast-in-place segment at the front support point of the hanging basket, apply constraints of U1=0 and U3=0, and simultaneously release the rotational degree of freedom around the transverse bridge direction by not constraining rotation in that direction.

[0092] Contact Pair Setup: In the steel-ECC composite structure region, define the outer surface of the steel plate shell element as the master face, and define the surface of the ECC solid element in contact with the steel plate as the slave face. Create contact properties: select hard contact for normal behavior, allowing separation after contact. Select penalized friction for tangential behavior, and enter a friction coefficient of 0.4. Simultaneously, in the slip tab of the contact properties, input the obtained bond-slip constitutive curve as a tangential stress-slip table.

[0093] After completing all settings, run a data check to confirm that there are no isolated nodes, duplicate elements, or elements without assigned attributes, and output the finite element model file in .inp or .cae format.

[0094] Further, S5 includes: Before the finite element analysis of the current construction phase begins, the hanging basket model element is activated and moved from the previous segment position to the current segment position. The moving operation is achieved by changing the node coordinates of the hanging basket element and regenerating the element connection relationship. Activate the concrete box girder solid element and steel bar element of the current segment, and at the same time activate the longitudinal prestressed duct element and prestressed steel strand element inside the current segment; After the current segment unit is activated, apply the self-weight load of the concrete in the current segment and apply the construction live load to the hanging formwork system. Perform finite element analysis for the current construction phase, use an incremental iterative solver to calculate the structural displacement field and stress field at the end of the phase, and extract the vertical displacements of the upper and lower edges of the front section of the current segment as the deformation for this phase from the solution results. After solving for the concrete self-weight and construction live load, a prestressing tension simulation is performed. The prestressing tension force is applied to the end nodes of the prestressed steel strand element in the form of an equivalent nodal load, or a temperature load is applied to the steel strand element using the cooling method to simulate the prestressing effect. The finite element solution is performed again to obtain the structural deformation increment after tensioning. This increment is added to the deformation before tensioning to obtain the final deformation of this stage. The displacement and stress values ​​of all nodes obtained in the current stage are saved as the initial state for the next stage, while the hanging basket element is blunted to simulate the process of the hanging basket moving forward to the next segment. Repeat the above activation, loading, solving, saving, and passivation operations until the construction stage simulation of all cantilevered segments is completed.

[0095] In this embodiment, the entire cantilever construction process is divided into 12 construction stages according to the actual construction sequence of the bridge: Stage 0 is the initial state after the completion of the zero block; Stage 1 is the pouring of segment 1; Stage 2 is the pouring of segment 2; and so on up to Stage 10, where segment 10 is poured; Stage 11 is the mid-span closure. Each stage is further subdivided into sub-steps; taking the pouring of segment 3 in Stage 3 as an example, the sub-step sequence in this stage is as follows: Sub-step 1 - move the formwork; Sub-step 2 - activate the segment unit; Sub-step 3 - apply self-weight and live load; Sub-step 4 - solve; Sub-step 5 - tension the prestress; Sub-step 6 - solve; Sub-step 7 - save the state and passivate the formwork.

[0096] In substep 1 of phase 3, the hanging basket movement is executed. A Python script is written to first read all element and node numbers of the hanging basket model. For each node, its coordinates X2, Y2, Z2 at the end of phase 2 are obtained. Then, the X coordinate is increased by 4m, the length of one segment, to obtain the new coordinates X2+4000, Y2, Z2. The node coordinates are updated using the editNode command. Since the coordinates have changed, the element connection relationship needs to be regenerated. The element topology is rebuilt based on the new node coordinates using the regenerateElements command. After the update is completed, the updateField command is executed to refresh the display.

[0097] In substep 2, activate the solid concrete box girder element of segment 3; locate the element set Segment3_Solid corresponding to segment 3 through the model tree and change its state attribute from deactivate to activate; similarly, activate the rebar element set Segment3_Rebar within segment 3. Activate the prestressed duct elements and prestressed tendon elements: duct element set Segment3_Duct, tendon element set Segment3_Tendon; the activation operation is performed in the ModelChange function of the finite element software, selecting the Activate option.

[0098] In substep 3, apply self-weight load: Enter the load module, select all activated concrete solid elements including block 0 and segments 1, 2, and 3, and apply gravity load with a gravity acceleration vector of 0, 0, -9800 mm / s². The program automatically calculates the nodal load based on the element volume and material density. Construction live load: Select all shell elements of the hanging basket formwork system and apply a uniformly distributed surface load of 2.5e-3 N / mm², equivalent to 2.5 kN / m², vertically downward. At the same time, apply a concentrated load at the front support point of the hanging basket to simulate the tension force at the front support point, with a value of 200 kN and a vertically upward direction.

[0099] Perform the finite element solution in substep 4; open the solver settings dialog box: select static-general for analysis type, automatic for time increment type, set the initial increment step size to 0.1, the minimum increment step size to 1e-6, the maximum increment step size to 1, and the maximum number of increment steps to 100; select the Newton-Raphson method as the solver, and enable the asymmetric matrix storage option to improve convergence; click submit to start the solution; monitor the residual norm and displacement correction norm during the solution process, and determine convergence when both are less than 1e-5; after the solution is completed, extract the vertical displacements of the upper and lower edge nodes at a position 4m×3=12m from the end face of block 0 at the front section of segment 3; the upper edge node is the node at the center of the top surface of the upper flange plate of this section, and the lower edge node is the node at the center of the bottom surface of the base plate; output the displacement values ​​to the text file Phase3_Displacement_BeforeTension.txt.

[0100] In substep 5, a prestressing tension simulation is performed; the equivalent nodal load is calculated: the prestressed steel strands use steel strands with a diameter of 15.2 mm, a single strand cross-sectional area of ​​140 mm², a total of 12 strands, and a total cross-sectional area of ​​1680 mm². The tension control stress is 1395 MPa, so the tension force is 1680 × 1395 = 2,343,600 N, approximately 2344 kN. This tension force is applied to the concrete by the anchors at both ends of the steel strand, equivalent to two equal and opposite concentrated forces acting on the anchor nodes at both ends of the steel strand. In the load module, the nodes at both ends of the steel strand unit are selected, and a concentrated force vector is applied, with the direction of stretching outward along the steel strand axis; considering the duct friction loss: according to the design drawings, the total steel strand rotation angle θ is 0.5 radians, the friction coefficient μ = 0.25, the fluctuation coefficient k = 0.0015, and the duct length L = 12 m, then the friction loss coefficient is calculated. = = = =0.867, the tension force after loss is 2344×0.867=2032kN; divide the corrected concentrated force value of 2032kN by 2 to get the force of 1016kN at each end, which is applied to the nodes at both ends of the steel strand; at the same time, considering the anchorage retraction loss of 6mm, according to the elastic modulus of the steel strand of 195GPa and the length of 12m, the stress loss Δσ=6 / 12000×195000=97.5MPa, which is equivalent to a loss force of about 164kN. The final equivalent node force is 1016-82=934kN at each end; after applying these loads, the solver of substep 6 is executed again, with the solver settings the same as substep 4; after solving, the vertical displacement of the same nodes is extracted and recorded as the displacement after tensioning. The displacement of substep 4 is added to the displacement increment of substep 6 to obtain the final deformation of stage 3.

[0101] In substep 7, the displacement fields U1, U2, U3 and stress fields S11, S22, S33, S12, S13, S23 of all nodes obtained in the current stage are written into a state file Phase3_State.odb; then, all element sets HangingBasket of the hanging basket model are set to the passivated state, and Deactivate is selected in Model Change; this operation does not delete elements, but only excludes them from the solution after the current stage, in order to simulate the process of the hanging basket moving to the next segment; the simulation of stage 3 is completed.

[0102] The simulations of stages 4 through 10 are completed sequentially. At the beginning of each new stage, the hanging basket unit is moved from the position of the previous stage to the position of the current stage. Then, the segment unit of the current stage is activated, the load is applied, the solution is obtained, the tension is applied, the state is saved, and the hanging basket is deactivated. After all stages are completed, the mid-span closure simulation of stage 11 is performed. The closure segment unit is activated, and the closure thrust is applied.

[0103] Further, S6 includes: The deformation of multiple key nodes is extracted from the post-processing results of the finite element model, and the extracted deformation is arranged to generate a sequence of data showing the change of deformation of each key node with the construction stage. For each construction stage, calculate the predicted vertical deflection and horizontal displacement of the front section of the current segment; Calculate the elastic deformation of the node at the front support point of the hanging basket and the axial deformation of each member of the main truss of the hanging basket. Use the elastic deformation of the front support point as the predicted deformation value of the hanging basket system. The deformation under different load conditions within the same construction stage is linearly superimposed. For the steel-ECC composite structure area, the relative displacement vector between the steel plate shell unit node and the adjacent ECC solid unit node in each construction stage is extracted. The component of the relative displacement vector in the tangential direction is calculated as the predicted value of inter-story slip, and the distribution curve of slip along the beam length is output. Output deformation prediction result file, recording the deformation values ​​of all key nodes in each construction stage, the overall deformation cloud map data of the structure after each construction stage, and the inter-story slip distribution data of the steel-ECC composite structure area after each construction stage. Calculate the deformation increment sequence between two adjacent construction stages and compare each deformation increment with the preset allowable deformation increment range; The predicted deformation values, the comparison results of deformation increments, and the out-of-limit markers are integrated into a structured output, which is saved in both text table format and binary cloud map format.

[0104] In this embodiment, after the solution is obtained at each construction stage, a post-processing script is automatically executed. The script first defines several node sets: The front support node set FB_front of the hanging basket includes four nodes at the connection between the front support anchor and the main truss of the hanging basket: left front, left rear, right front, and right rear.

[0105] The current segment front section node set Seg_front: the upper edge node has 5 points equidistant along the transverse direction of the bridge, with coordinates of the bridge centerline, 2m to the left and 4m to the right, and the lower edge node also has 5 points.

[0106] Midspan, the node set for the mid-span closure of the completed segment: Select one node each for the top plate and bottom plate at the center of block zero.

[0107] The hanging basket back anchor point node set FB_back contains nodes at 4 back anchor point positions.

[0108] Steel-ECC composite structure region interface node pair set ECC_interface: At each steel-ECC interface location, search for steel plate nodes and ECC nodes with a distance of less than 0.01mm to form a node pair.

[0109] The script reads the current displacement values ​​U1, U2, U3 of each node from the results database .odb file, and also reads the displacement value of the node at the end of the previous stage from the status file, calculates the displacement increment, and writes the current displacement value into a dictionary with the construction stage number and node name as the keys and the displacement component as the values.

[0110] Arrange the deformation values ​​of each node into a sequence according to the construction stages from 1 to 10. For example, the vertical displacement sequence of the center node at the upper edge of the front section of node Seg_front_up_center is: U3 value of stage 1, U3 value of stage 2, ..., U3 value of stage 10; write this sequence into the first worksheet Displacement_Sequence of the output file. The sequence for each node is in a separate column, with the row number being the stage number.

[0111] For each construction stage, calculate the predicted vertical deflection value of the front section of the current segment: V_deflection=(average(U3 of 5 upper nodes)+average(U3 of 5 lowernodes)) / 2 That is, take the arithmetic mean of the average value of the 5 upper edge nodes U3 and the average value of the 5 lower edge nodes U3.

[0112] The predicted horizontal displacement is taken as the U1 value of the node at the intersection of the bridge centerline and the cross section at the front section center node, representing the bridge's longitudinal displacement.

[0113] Write these two values ​​into the Predicted_Deflections worksheet in the output file. Each row corresponds to a stage, and the columns include the stage number, the predicted vertical deflection value (mm), and the predicted horizontal displacement value (mm).

[0114] Extract the U3 values ​​of the four nodes at the front support point of the hanging basket and calculate their arithmetic mean as the elastic deformation of the front support point. Extract the axial deformation of each member of the main truss of the hanging basket: For each member, obtain the displacements of its two end nodes A and B, and calculate the projection difference of the vector from A to B along the undeformed member axis. Specifically, let the original direction vector of the member be d0, and the displacement difference vector between the two end nodes be Δu, then the axial deformation = Δu·d0 / |d0|. Output the axial deformation of all members to the HangingBasket_Deformation worksheet.

[0115] For the same construction phase, four analysis steps with different load conditions are established in the finite element solver: Working condition 1: Only gravity load is applied, excluding live load, prestress, and the self-weight of the formwork. Condition 2: Only construction live load is applied Condition 3: Only prestressed load is applied Condition 4: Only the weight of the hanging basket is applied, and the density of the hanging basket is set to the actual value; the densities of other materials are set to zero. After solving each working case, the displacement field is output; then, the nodal displacements are superimposed: for each node, the total displacement U_total = U_gravity + U_live + U_prestress + U_basket_self. The superimposed displacements are written to the Superimposed_Displacement worksheet.

[0116] For each pair of nodes in the steel-ECC composite structure region, including plate node P and ECC node C, read the displacement vector U_p of P and the displacement vector U_c of C, and calculate the relative displacement vector ΔU = U_p - U_c. Establish a local coordinate system at node P: take the normal vector of the plate shell element at this node as the local Z-axis, the length direction of the steel plate along the bridge direction as the local X-axis, and the width direction as the local Y-axis. Calculate the components of ΔU on the local X-axis and local Y-axis, and take sqrt(ΔUx² + ΔUy²) as the tangential slip. Along the beam length direction, from the end of the starting segment to the end segment within a 3m range, take a section every 0.1m, calculate the average slip of all nodes on that section, and take it as the slip of that section. Correspond the distance of the section position from the end of the segment to the slip, and output a text file Slip_Distribution_PhaseX.txt, each file containing two columns of data: distance (mm) and slip (mm). Simultaneously, the slip data of all cross sections were plotted as curves and saved as .png images.

[0117] Generate an Excel file named Deformation_Prediction_Result.xlsx containing the following worksheets: Displacement_Sequence: Displacement values ​​of key nodes at each construction stage. Predicted_Deflections: Predicted vertical deflection and predicted horizontal displacement. Incremental_Comparison: Comparison of the calculated value of the deformation increment between adjacent stages with the allowable range. Out_of_Tolerance_Marks: List of out-of-tolerance markers Simultaneously, a binary cloud map file, Deformation_Cloud_PhaseX.vtk, is generated, with one file for each stage. It contains the displacement and stress fields of the nodes and can be opened with ParaView software.

[0118] In the Incremental_Comparison worksheet, for each construction stage ii≥2, calculate the vertical deflection increment ΔV=V_i-V_{i-1}, with a preset maximum allowable increment ΔV_max=15mm. If ΔV>15mm, add a row to the Out_of_Tolerance_Marks worksheet: Stage i, vertical deflection increment at the front section ΔV=XXmm, exceeding limit +XXmm. The horizontal displacement increment is handled similarly, with a maximum allowable value of 5mm.

[0119] Finally, all the above data is integrated into a single compressed file, with the filename including the date and bridge name.

[0120] Furthermore, the front support hanging basket includes a main truss system, a front support anchoring system, a rear anchoring system, a traveling system, and a formwork system. In the finite element model, the front support position of the front support hanging basket is connected to the lower edge node of the cast-in-place box girder segment through anchor rod elements. The anchor rod elements are set as rod elements that only bear tensile forces. The rear anchor point is connected to the upper edge node of the cast box girder segment through a fine-rolled threaded steel unit. The fine-rolled threaded steel unit is set as a rod unit that only bears tensile force. During the simulated movement of the hanging basket, the forward movement of the hanging basket is achieved by changing the activation state of the front support anchor bolt unit and the rear anchor fine-rolled threaded steel unit.

[0121] In this embodiment, the main truss system of the front support hanging basket adopts a double-piece triangular truss. In the finite element model, the main longitudinal beam of each truss is simulated using B31 beam elements, with a cross-section of HN400×200×8×13 steel, a cross-sectional area of ​​84.12 cm², and a moment of inertia Ix = 23700 cm. 4 The front and rear diagonal braces are made of HN300×150×6.5×9 steel with a cross-sectional area of ​​58.06 cm²; the vertical members are made of HW200×200×8×12 steel. The transverse connection between the two trusses uses I20a I-beam units.

[0122] Front Support Anchoring System: Two anchor rods are installed at the front support location. Each anchor rod is simulated using T3D2 rod elements with a circular cross-section of 32mm diameter and made of high-strength threaded steel with a yield strength of 930MPa. The lower node of the anchor rod is connected to the node on the front crossbeam of the hanging basket, and the upper node is connected to the lower edge node of the already cast box girder segment. The anchor rod element is set to withstand only tensile force: the "no compression" option is defined in the element properties, meaning that when the calculated axial force is negative, the element stiffness is set to zero.

[0123] Rear anchor system: Four precision-rolled threaded steel bars are installed, using T3D2 rod units, with a diameter of 32mm and the same material as before; the lower end of each precision-rolled threaded steel bar is connected to the spreader beam node of the rear anchor point of the hanging basket, and the upper end is connected to the upper edge node of the already cast box girder segment; it is also set to only bear tensile force.

[0124] Walking system: Two walking tracks are simulated using S4R shell elements. The bottom surface of the tracks contacts the top plate of the box girder, and the contact property is set to frictionless. The top surface of the tracks contacts the traveling wheels of the hanging basket, which are simulated using a sliding constraint that only allows movement along the track direction.

[0125] Template system: The bottom formwork platform is composed of beam elements forming a grid with a grid size of 1m×1m, and covered with a layer of shell elements to simulate the bottom formwork steel plate; the side formwork and inner formwork are simulated using shell elements.

[0126] When simulating the movement of the hanging basket, the activation states of the anchor bolts and the precision-rolled threaded steel units need to be changed sequentially. Taking the movement from segment 2 to segment 3 as an example: Step A: After the construction and tensioning of segment 2 are completed, the state of the anchor bolt unit set of the front support point of segment 2 in the current stage, named Anchor_2, is set to deactivate.

[0127] Step B: Set the state of the set of fine-rolled threaded steel units at the rear anchor point of segment 2 to Post_2 and set it to passivation.

[0128] Step C: Create a new anchor element set Anchor_3 at segment 3. Creation method: Copy the element definition of Anchor_2, but modify the coordinates of its two end nodes. The new node coordinates are obtained as follows: The coordinates of the lower edge node of segment 3 already exist; the coordinates of the nodes of the front crossbeam of the hanging basket at the current position after movement are obtained through coordinate updates; set the I node of the anchor element as the hanging basket node, and the J node as the lower edge node. After generating the element, set its attribute to tension-only element. Activate Anchor_3.

[0129] Step D: Similarly, create the Post_3 fine-rolled threaded steel unit set, connect the back anchor point of the hanging basket to the upper edge node of segment 3, and activate it.

[0130] During state transitions, all units of the main truss system remain active and are not deactivated. Node coordinate updates for the main truss system are implemented via a coordinate translation script, with the translation amount equal to the segment length of 4m. When executing coordinate updates, the order is to first update the node coordinates and then regenerate the unit connection relationships to ensure correct unit topology.

[0131] The forward movement of the hanging basket is not completed in one go, but is divided into multiple sub-steps to simulate the actual walking process; in the finite element model, the movement process is divided into 10 sub-steps, each sub-step moving 0.4m. Within each sub-step: Calculate the target coordinates at the end of the current substep: X_new = X_initial + 0.4m × substep number.

[0132] Update the X coordinates of all nodes in the main truss system of the hanging basket to X_new.

[0133] Update the node coordinates of the front support anchor bolt and rear anchor bolt precision rolled threaded steel unit. The nodes of these units include hanging basket nodes and box girder nodes, among which the coordinates of the box girder nodes remain unchanged.

[0134] Perform a static solution considering only the self-weight, and check whether the structure is stable, the displacement converges, and there are no negative principal element warnings.

[0135] If convergence is achieved, proceed to the next substep; if convergence is not achieved, halve the movement increment by 0.2m and try again.

[0136] After completing all 10 sub-steps, the basket moves to the target position; then the activation of the new segment and pouring operation are performed.

[0137] Furthermore, the simulation of segment-by-segment concrete pouring and segment-by-segment prestressing in S5 includes: In the finite element analysis of each construction stage, the concrete pouring process is decomposed into multiple sub-steps, and the gradual change process of concrete from the fluid state to the hardened state is simulated step by step. After the concrete material properties are switched, an analysis step is performed to simulate the concrete curing process. After the maintenance analysis step is completed, activate the longitudinal prestressed steel strand unit in the current segment, and connect the prestressed steel strand unit with the surrounding concrete unit through embedded constraints or common nodes. The prestressing tension simulation adopts the equivalent load method. The equivalent nodal force at both ends of the steel strand is calculated based on the tension control stress. The equivalent nodal force is applied to the end nodes of the steel strand element, and the loss effect is simulated by correcting the value of the equivalent nodal force. After all analysis steps are completed in each construction phase, the structural stiffness matrix, internal force vector, and displacement field of the current phase are completely transferred to the next phase as the initial conditions for the next phase analysis.

[0138] In this embodiment, taking the pouring of segment 3 as an example, the pouring process is broken down into three sub-steps.

[0139] Sub-step A: Empty Box Girder Activation: Activate the Seg3_Solid solid element set of the concrete box girder in segment 3, but do not assign it a real ECC material constitutive model at this time. Instead, assign it a temporary material TEMP_MAT; the elastic modulus of this material is set to an extremely low 1MPa, Poisson's ratio to 0.2, and density to 2500kg / m³. The density value is kept the same as that of real concrete to ensure the correct self-weight load. Perform a static solution, applying only gravity, to obtain the initial displacement field for this stage. The purpose of this step is to allow the empty box girder formwork to bear its own weight without generating excessive stiffness resistance.

[0140] Substep B Material Property Switching: Switch the material properties of the Seg3_Solid elements from TEMP_MAT to the actual ECC material constitutive model. This switching is achieved by modifying the section property pointers of each element. In finite element software, a new section assignment (ECC_Section) can be created and assigned to the Seg3_Solid element set, while deleting the original temporary section assignment. After the switch, perform a restart analysis, using the displacement field at the end of substep A as the initial condition, applying a gravity load, and solving. During the solution process, non-convergence may occur due to a sudden increase in material stiffness. In this case, reduce the increment step size to 0.01 and increase the number of iterations to 30.

[0141] Substep C: Applying Self-Weight and Live Load: After the material switching is completed and convergence is achieved, proceed to the third substep. In this substep, the constitutive model of the ECC material remains unchanged, and the full self-weight load and construction live load are applied.

[0142] After substep C is completed, a dedicated analysis step is added to simulate the curing process. This analysis step lasts 28 days, corresponding to the actual curing time, but a true time history analysis is not performed in the finite element analysis; instead, creep and shrinkage models are used for equivalence. Specific steps: Add a creep model to ECC in the material properties, select the time hardening mode, and set the parameters C1=1.0e-5, C2=0.5, and C3=0.0. These parameters are calibrated based on ECC material tests.

[0143] Add a contraction model, select exponential contraction, and set the final contraction strain to 400 × 10⁻⁶. -6 The contraction half-life is taken as 10 days.

[0144] Create a Visco analysis step with a duration of 28 days and a time increment method of fixed increment step, with one increment step per day, for a total of 28 increment steps.

[0145] No new loads are applied in this analysis step; only creep and shrinkage strains are allowed to develop over time. The stress and displacement fields are updated at the end of each increment step.

[0146] After the curing analysis step is completed, the displacement and stress at this point are used as the initial state for the subsequent tension analysis.

[0147] After curing, a prestressing tension simulation was conducted. The equivalent load method was adopted, but the losses from duct friction and anchor retraction were further refined to take into account.

[0148] First, determine the geometric path of the prestressed steel strands: the steel strands are in the form of curves and are arranged in a wavy shape within the web of the box girder; the steel strands are discretized into multiple straight line segments, and each straight line segment is simulated using a T3D2 bar element; the method of applying equivalent nodal forces on each bar element needs to be decomposed according to the angle between the element and the global coordinate system.

[0149] Segment-by-segment calculation considering duct friction loss: Starting from the tensioning end, the friction loss of the first element is 0, and the loss coefficient of the second element is... , where θ is the cumulative rotation angle of the previous segment and l is the length of the current segment; calculate the effective tension force for each element; after the loss coefficient is calculated, convert the effective tension force into an equivalent nodal load vector: apply a concentrated force of equal magnitude and direction along the element axis to the two nodes of each element, with the direction away from the element center to simulate tension.

[0150] Considering anchorage retraction loss: the retraction amount is taken as 6mm, and the length of the retraction influence is determined by solving the equation: retraction amount = ∫(stress loss / elastic modulus) integral along the strand length; the iterative method is used to solve it: first assume the influence length is L_eff, calculate the stress loss distribution, then integrate to find the retraction amount, adjust L_eff until the error between the calculated retraction amount and 6mm is less than 0.1mm; finally, the actual effective prestress of each node is obtained.

[0151] After completing the loss correction, the corrected nodal forces are applied to the finite element model, and a static solution is performed to obtain the deformation after tensioning.

[0152] After all analysis steps (casting sub-steps A, B, and C), curing analysis step, and tensioning analysis step) of each construction phase are completed, the final structural stiffness matrix, internal force vectors, and displacement field are written into a transfer file. In the initial analysis of the next phase, this transfer file is read as the initial conditions. Specifically, in the finite element software's restart function, select to continue from the end state of the previous phase and specify the path to the transfer file. In this way, at the start of the next phase, the stress, strain, and displacement of all elements are continuously inherited without recalculation.

[0153] Furthermore, the method also includes: Based on the deformation prediction value of each construction stage, a formwork elevation correction table is generated for the cantilever construction of the front support hanging basket. The formwork elevation correction table includes the segment number of each cantilever segment, the design formwork elevation, the predicted vertical deflection value, and the corrected formwork elevation. The formwork elevation correction table also includes the predicted inter-layer slip of the steel-ECC composite structure area corresponding to each segment, as well as the pre-lifting value of the formwork system suggested based on the predicted inter-layer slip.

[0154] In this embodiment, the vertical deflection prediction values ​​for each construction stage are read from the output deformation prediction result file Deformation_Prediction_Result.xlsx, specifically from the vertical deflection prediction value column in the Predicted_Deflections worksheet. Simultaneously, the design formwork elevation for each cantilever segment is read from the construction drawings.

[0155] The header of the formwork elevation correction table includes the following: Segment numbered 1 to 10 The design elevation of the vertical mold is in mm, relative to a certain reference point, such as the top surface elevation of block zero + 5000 mm; Predict the vertical deflection value in mm, and take the predicted vertical deflection value of the front section of the corresponding stage; The corrected formwork elevation (mm) is calculated using the formula: Design formwork elevation - Predicted vertical deflection value; The predicted value of inter-layer slip in the steel-ECC composite structure area (in mm) is taken from the slip at the section 0.5m from the end of the segment in the output Slip_Distribution_PhaseX.txt file. It is recommended that the pre-lift value of the template system (in mm) be 1.2 times the predicted value of inter-story slippage; For each segment, perform the following calculations: Segment 1: Design formwork elevation = 5000mm, predicted vertical deflection value = 12.3mm (example). Corrected formwork elevation = 5000 - 12.3 = 4987.7mm. The slippage at 0.5m from the end, read from the slip distribution file, is 1.8mm. Suggested pre-lift value = 1.8 × 1.2 = 2.16mm, rounded to 2.2mm.

[0156] Fill the table with the calculation results for all segments. Save the table in Excel format, named Formwork_Elevation_Correction.xlsx. Also output a copy in CSV format for importing into the total station.

[0157] Generate a text-formatted construction control parameter file, Construction_Control_Parameters.txt, which includes the prestressing tensioning sequence and tension force application scheme for each construction stage.

[0158] Method for determining the tensioning sequence: From the output Incremental_Comparison worksheet, obtain the magnitude of the deformation increment caused by applying prestress to the web tendon, top tendon, and bottom tendon at each tendon location. For example, for segment 3, tensioning the web tendon causes a downward displacement of 5.2 mm at the front end section, tensioning the top tendon causes a downward displacement of 2.1 mm, and tensioning the bottom tendon causes an upward displacement of 1.5 mm. Sort the tensioning sequences from largest to smallest absolute value of the deformation increment: tension the web tendons first, then the top tendons, and finally the bottom tendons. Write this sequence into the parameter file.

[0159] Tension force application scheme: To avoid concrete cracking caused by applying the full tension force at once, the total tension force is divided into three levels: Level 1 applies 30%, Level 2 applies 30%, and Level 3 applies 40%. A 30-second hold step is set between each level for the finite element model to perform equilibrium iterations. The format of the parameter file is as follows: Phase 3, steel strand group: FB-01 web strand, grade 1: 30% load value = 300kN, grade 2: 30% load value = 300kN, grade 3: 40% load value = 400kN, with a 30-second interval between each grade.

[0160] Repeat the above steps for each steel strand group at each construction stage.

[0161] Package the formwork elevation correction table (Excel file), construction control parameter file (Text file), output deformation prediction result file (Excel file), and binary cloud map into a single folder. The folder name should be in the format: Bridge Name_Construction Control Data_Date. Create a README.txt file within this folder, explaining the purpose of each file. Formwork_Elevation_Correction.xlsx: Used for on-site formwork elevation adjustment, and is issued to the surveying team before the construction of each segment.

[0162] Construction_Control_Parameters.txt: Used by prestressed tensioning teams to guide the tensioning sequence and graded loading.

[0163] Deformation_Prediction_Result.xlsx: Contains detailed deformation prediction data for each stage, for analysis by the monitoring team.

[0164] Deformation_Cloud_PhaseX.vtk: Cloud map file used for 3D visualization inspection.

[0165] Copy the entire folder to a portable storage device and deliver it to the technical supervisor at the bridge construction site. Simultaneously, upload a backup copy through the project management platform.

[0166] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for predicting deformation during cantilever construction using a front-support hanging basket based on finite element simulation, characterized in that, Includes the following steps: S1: Obtain the compressive strength, tensile strength, and flexural strength of the engineering cement-based ECC composite material, determine the strength characteristics and ductile deformation properties based on the stress-strain curves obtained from the experiment, and construct the constitutive model of the ECC material; S2: Obtain the static shear performance of short studs in steel-ECC composite structures, measure the shear capacity, shear stiffness and slip capacity of the ejected specimens, analyze the influence of interlaminar bond between steel and ECC on shear performance, and obtain the static shear parameters of short studs; S3: Obtain the local bending performance of the steel-ECC composite structure under positive and negative bending moment loading conditions. Measure the bending capacity, relative slip capacity, and crack resistance of the composite structure under different protective layer thicknesses and reinforcement ratios to obtain the local bending performance parameters under positive and negative bending moment loading conditions. S4: Establish a finite element model of the cantilever construction process of the front support hanging basket, and input the constitutive model of the ECC material, static shear parameters and local bending performance parameters into the finite element model; S5: Simulate the cantilever construction process of the front support hanging basket, including moving the hanging basket segment by segment, pouring concrete segment by segment, and tensioning prestress segment by segment, and calculate the deformation of each construction stage. S6: Output the predicted deformation value of the cantilever construction process of the front support hanging basket based on the deformation amount of each construction stage.

2. The method according to claim 1, characterized in that, In S1, a prism specimen is used, and axial pressure is applied until the specimen fails. The peak load and the corresponding axial compressive strain are recorded. The compressive strength is calculated based on the ratio of the peak load to the bearing area of ​​the specimen. A dog-bone shaped plate specimen was used. Axial tension was applied to both ends of the specimen, and tensile strain within the gauge length was measured using an extensometer to obtain the full curve of tensile stress versus tensile strain. The elastic modulus, peak tensile stress, and ultimate tensile strain were extracted from the full curve as parameters for tensile strength characteristics and ductile deformation properties. A beam-type specimen was used, and two symmetrical loads were applied to the mid-span region at the bottom of the specimen. The relationship curve between the load and the mid-span deflection was measured. The bending strength and bending toughness index were calculated according to the bending stress formula. The bending toughness index was determined by the ratio of the area under the load-deflection curve to the area corresponding to the first cracking load.

3. The method according to claim 1, characterized in that, S2 includes the following operations: Prepare a steel-ECC composite specimen by welding short studs to the upper surface of the steel plate and casting ECC material on top of the steel plate to form an ECC plate, so that the short studs are completely embedded in the ECC plate; The ejected specimen was installed in a universal testing machine. A vertical ejection load was applied to the end of the steel plate. Two linear variable differential transformers were symmetrically arranged on both sides of the specimen to measure the relative slip between the steel plate and the ECC plate. Continuous loading was performed using displacement control, and the load-slip curves were recorded throughout the entire process. Shear capacity is extracted from the load-slip curve as the peak load value of the curve, shear stiffness is extracted as the slope value of the straight part of the rising segment of the curve, and slip capacity is extracted as the slip amount corresponding to the peak load and the ultimate slip amount. By preparing multiple sets of ejection specimens with different interface treatments, comparing the differences in load-slip curves among the specimens, analyzing the influence of interlaminar bonding on shear capacity, shear stiffness, and slippage capacity, and obtaining modified static shear parameters considering the interlaminar bonding effect.

4. The method according to claim 1, characterized in that, S3 includes: Steel-ECC composite beam specimens were prepared, with multiple different values ​​for protective layer thickness and multiple different values ​​for reinforcement ratio; For positive bending moment loading, the composite beam specimen is simply supported on two supports, and vertical loads are applied at two symmetrical points in the mid-span region of the beam, so that the bottom steel plate of the beam is under tension and the top ECC is under compression. For negative bending moment loading, the two ends of the composite beam specimen are constrained by fixed supports, and vertical loads are applied at two symmetrical points in the mid-span region of the beam, so that the top ECC of the beam is under tension and the bottom steel plate is under compression. Alternatively, the original positive bending moment specimen can be flipped over and loaded using an inverted simply supported method. Displacement control mode was used during both positive and negative bending moment loading processes. The loading rate was controlled to keep the rate of increase of mid-span deflection constant. The load values ​​of the load sensor, the deflection values ​​of the linear variable differential transformer arranged at mid-span, the relative slip of the slip measurement points arranged on multiple sections along the beam length, and the development of surface cracks in the ECC layer were continuously recorded. The flexural bearing capacity is determined based on the recorded load-mid-span deflection curve. The flexural bearing capacity includes the cracking load value when the first crack appears, the peak load value on the curve, and the residual load value corresponding to a specific deflection-ductility ratio after the peak load. Based on the relative slip measured at multiple cross sections, a slip distribution curve along the beam length is plotted, and the maximum slip is extracted from the distribution curve as the relative slip capacity of the specimen. During the loading process, the load value at which the first visible crack appeared on the surface of the ECC layer was recorded using a magnifying glass and a crack observation instrument as the crack initiation load. The average and maximum values ​​of the crack spacing were measured, and the rate of change of the crack width with the increase of the load was measured to obtain crack resistance indicators including crack initiation load, crack spacing range, and crack width growth rate. The flexural bearing capacity, relative slip capacity, and crack resistance obtained under all positive bending moment conditions are summarized as local flexural performance parameters under positive bending moment conditions, and the corresponding indices obtained under all negative bending moment conditions are summarized as local flexural performance parameters under negative bending moment conditions.

5. The method according to claim 1, characterized in that, S4 includes: A three-dimensional geometric model was established based on the structural design drawings of the front support hanging basket and the construction drawings of the bridge cantilever segment; The main truss members of the hanging basket are meshed using beam elements, the front support anchor rods and rear anchor threaded steel bars are meshed using rod elements, the traveling track is meshed using shell elements, the concrete box girder segments are meshed using solid elements, and the steel plates in the steel-ECC composite structure area are meshed using shell elements, the ECC layer is meshed using solid elements, and the short studs are meshed using spring elements. A contact pair is established on the contact surface between the steel plate element and the solid element of the ECC layer. The normal behavior of the contact pair is defined as hard contact, and the tangential behavior is defined as penalty friction. The static shear parameters obtained from the push-out test are converted into the stiffness properties of the spring element or the bond slip constitutive curve of the contact pair. The constitutive model of ECC material is assigned to the solid elements of ECC layer, and the bilinear elastoplastic constitutive model of steel is assigned to the steel plate shell elements and steel bar elements. Displacement constraints are applied at the boundaries of the model, including fixed-end constraints at the ends of the zero block segments that have been poured, vertical and longitudinal fixed constraints at the anchor points of the hanging basket, and rolling support constraints that allow only vertical movement at the front support points of the hanging basket.

6. The method according to claim 1, characterized in that, S5 includes: Before the finite element analysis of the current construction phase begins, the hanging basket model element is activated and moved from the previous segment position to the current segment position. The moving operation is achieved by changing the node coordinates of the hanging basket element and regenerating the element connection relationship. Activate the concrete box girder solid element and steel bar element of the current segment, and at the same time activate the longitudinal prestressed duct element and prestressed steel strand element inside the current segment; After the current segment unit is activated, apply the self-weight load of the concrete in the current segment and apply the construction live load to the hanging formwork system. Perform finite element analysis for the current construction phase, use an incremental iterative solver to calculate the structural displacement field and stress field at the end of the phase, and extract the vertical displacements of the upper and lower edges of the front section of the current segment as the deformation for this phase from the solution results. After solving for the concrete self-weight and construction live load, a prestressing tension simulation is performed. The prestressing tension force is applied to the end nodes of the prestressed steel strand element in the form of an equivalent nodal load, or a temperature load is applied to the steel strand element using the cooling method to simulate the prestressing effect. The finite element solution is performed again to obtain the structural deformation increment after tensioning. This increment is added to the deformation before tensioning to obtain the final deformation of this stage. The displacement and stress values ​​of all nodes obtained in the current stage are saved as the initial state for the next stage, while the hanging basket element is blunted to simulate the process of the hanging basket moving forward to the next segment. Repeat the above activation, loading, solving, saving, and passivation operations until the construction stage simulation of all cantilevered segments is completed.

7. The method according to claim 1, characterized in that, S6 includes: The deformation of multiple key nodes is extracted from the post-processing results of the finite element model, and the extracted deformation is arranged to generate a sequence of data showing the change of deformation of each key node with the construction stage. For each construction stage, calculate the predicted vertical deflection and horizontal displacement of the front section of the current segment; Calculate the elastic deformation of the node at the front support point of the hanging basket and the axial deformation of each member of the main truss of the hanging basket. Use the elastic deformation of the front support point as the predicted deformation value of the hanging basket system. The deformation under different load conditions within the same construction stage is linearly superimposed. For the steel-ECC composite structure area, the relative displacement vector between the steel plate shell unit node and the adjacent ECC solid unit node in each construction stage is extracted. The component of the relative displacement vector in the tangential direction is calculated as the predicted value of inter-story slip, and the distribution curve of slip along the beam length is output. Output deformation prediction result file, recording the deformation values ​​of all key nodes in each construction stage, the overall deformation cloud map data of the structure after each construction stage, and the inter-story slip distribution data of the steel-ECC composite structure area after each construction stage. Calculate the deformation increment sequence between two adjacent construction stages and compare each deformation increment with the preset allowable deformation increment range; The predicted deformation values, the comparison results of deformation increments, and the out-of-limit markers are integrated into a structured output, which is saved in both text table format and binary cloud map format.

8. The method according to claim 1, characterized in that, The front support hanging basket includes a main truss system, a front support anchoring system, a rear anchoring system, a traveling system, and a formwork system. In the finite element model, the front support position of the front support hanging basket is connected to the lower edge node of the cast-in-place box girder segment through anchor rod elements. The anchor rod elements are set as rod elements that only bear tensile forces. The rear anchor point is connected to the upper edge node of the cast box girder segment through a fine-rolled threaded steel unit. The fine-rolled threaded steel unit is set as a rod unit that only bears tensile force. During the simulated movement of the hanging basket, the forward movement of the hanging basket is achieved by changing the activation state of the front support anchor bolt unit and the rear anchor fine-rolled threaded steel unit.

9. The method according to claim 1, characterized in that, The simulation of segment-by-segment concrete pouring and segment-by-segment prestressing in S5 includes: In the finite element analysis of each construction stage, the concrete pouring process is decomposed into multiple sub-steps, and the gradual change process of concrete from the fluid state to the hardened state is simulated step by step. After the concrete material properties are switched, an analysis step is performed to simulate the concrete curing process. After the maintenance analysis step is completed, activate the longitudinal prestressed steel strand unit in the current segment, and connect the prestressed steel strand unit with the surrounding concrete unit through embedded constraints or common nodes. The prestressing tension simulation adopts the equivalent load method. The equivalent nodal force at both ends of the steel strand is calculated based on the tension control stress. The equivalent nodal force is applied to the end nodes of the steel strand element, and the loss effect is simulated by correcting the value of the equivalent nodal force. After all analysis steps are completed in each construction phase, the structural stiffness matrix, internal force vector, and displacement field of the current phase are completely transferred to the next phase as the initial conditions for the next phase analysis.

10. The method according to claim 1, characterized in that, Also includes: Based on the deformation prediction values ​​of each construction stage, a formwork elevation correction table is generated for the cantilever construction of the front support hanging basket. The formwork elevation correction table includes the segment number of each cantilever segment, the design formwork elevation, the predicted vertical deflection value, and the corrected formwork elevation. The formwork elevation correction table also includes the predicted inter-layer slip of the steel-ECC composite structure area corresponding to each segment, as well as the pre-lifting value of the formwork system suggested based on the predicted inter-layer slip.

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