A precast composite support design and construction control method considering eccentricity

Abstract

This invention relates to a design and construction control method for prefabricated composite supports considering eccentricity, comprising: 1. Pre-embedding strain sensors in the middle and ends of segments to ensure that the deviation between the centroid of the steel frame and the centroid of the concrete in each segment is ≤L / 5000, where L is the segment length; measuring and recording the measured value e0 of the initial centroid eccentricity before leaving the factory; 2. Determining the axial force distribution coefficient of the steel frame based on the stiffness ratio; calculating the additional bending moment Madd caused by centroid eccentricity under axial pressure P using e0; calculating the ultimate bearing capacity Pmax based on Madd and P; 3. Collecting the strain of the steel frame and concrete in layers during foundation pit excavation, and measuring the horizontal displacement Δ of the diaphragm wall at the support elevation; calculating the additional bending moment M during construction based on Δ. Δ M Δ The total bending moment M is obtained by superimposing Madd, and the crack width w is calculated from M; the actual eccentricity e during the construction stage is calculated from the measured strain. a , will e a Compare with e0 and check the cross-sectional stress; IV. Take control measures as appropriate.

Description

Technical Field

[0001] This invention belongs to the field of building construction technology, and specifically relates to a design and construction control method for prefabricated combined supports that takes eccentricity into account. Background Technology

[0002] In foundation pit and tunnel engineering, precast steel-concrete composite supports are widely used due to their advantages of high strength, rapid assembly, and reusability. However, for ultra-long, large-section components, a fundamental accuracy problem exists during segmented prefabrication in the factory: the centroid of the internal steel frame and the centroid of the outer concrete casing are difficult to perfectly coincide. Traditional design treats the composite section as a whole, calculating based on an ideal model of "plane section assumption" and "centroid coincidence." This ignores the additional internal forces caused by centroid eccentricity. The component degenerates from an ideal axial compression state to an actual eccentric compression state, resulting in a significant and unpredictable reduction in its stable bearing capacity and section strength. Current design methods typically use a generally increased safety factor for compensation, leading to designs that are either conservative and wasteful or contain hidden risks.

[0003] Additional eccentricity induced by foundation pit deformation during the construction phase also poses risks. After the combined support is installed, the diaphragm wall undergoes horizontal displacement under earth pressure as the foundation pit is excavated. Since the supports are connected to the diaphragm wall at both ends, the displacement of the diaphragm wall causes bending deformation in the supports, further increasing the additional bending moment inside the components, leading to crack development, stiffness degradation, and even instability failure. Traditional design methods typically ignore the impact of diaphragm wall displacement on the internal forces of the supports during construction, fail to establish a quantitative relationship between support crack width and bearing capacity, and lack targeted stress monitoring and control methods.

[0004] Therefore, how to provide a design and construction control method for prefabricated composite supports that takes into account eccentricity is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention provides a prefabricated composite support design and construction control method that takes eccentricity into account. It constructs a unified, process-driven, and closed-loop intelligent digital twin management and control platform for the entire process of deep foundation pit construction, solving the problems of collaborative management and forward-looking decision-making in the construction process.

[0006] To solve the above technical problems, the present invention includes the following technical solutions:

[0007] A design and construction control method for precast reinforced concrete composite supports considering eccentricity, wherein the precast composite supports include an internal steel frame and an outer concrete casing, the method comprising:

[0008] Factory processing stage: When prefabricating each segment, strain sensors are pre-embedded in the middle and ends of the segment. CNC positioning fixtures are used to ensure that the deviation between the centroid of the steel frame and the centroid of the concrete of each segment is ≤L / 5000, where L is the segment length. Before leaving the factory, the initial centroid eccentricity e0 is measured and recorded by three-dimensional laser scanning. e0 can be recorded on the component information plate.

[0009] Design verification stage: Calculate the bearing capacity reduction formula under manufacturing eccentricity, regard the prefabricated composite support as a compression member composed of steel and concrete, and determine the axial force distribution coefficient α of the steel frame according to the stiffness ratio; use e0 to calculate the additional bending moment Madd caused by centroidal eccentricity under axial pressure P; calculate the ultimate bearing capacity Pmax based on Madd and P as an eccentrically compressed member, and ensure that the design axial force is not greater than Pmax.

[0010] During the construction monitoring phase: Strain sensors were installed at both ends of the support and at the mid-span section. Strain data for the steel frame and concrete was collected layer by layer as the foundation pit was excavated, and the horizontal displacement Δ of the diaphragm wall at the support elevation was also acquired. The additional bending moment MΔ was calculated based on Δ, and MΔ was superimposed with Madd to obtain the total bending moment M. The crack width w was then calculated from M. Simultaneously, the actual eccentricity e during the construction phase was calculated from the measured strain. a , will e a Compare with e0 and check the cross-sectional stress;

[0011] Construction control phase: When the crack width w exceeds the preset limit, or e a When the stress exceeds the set multiple of e0, or when the measured cross-sectional stress exceeds the stress limit, control measures shall be taken.

[0012] In this embodiment, more preferably, the control measures include adjusting the excavation sequence, adding temporary supports, and / or installing arc-shaped steel support plates between the support ends and the diaphragm wall.

[0013] In this embodiment, more preferably, the allocation coefficient α is given by the formula α=(E s A s ) / ( E s A s +E c A c The values ​​are determined as follows: Es and Ec are the elastic moduli of steel and concrete, respectively, and As and Ac are the cross-sectional areas of steel and concrete, respectively.

[0014] In this embodiment, more preferably, the ultimate bearing capacity Pmax is obtained by making the maximum compressive stress at the edge of the cross-section reach the material strength design value f, satisfying the formula Pmax=f / [1 / A + (α·e0) / W], where A=A s +A c W is the equivalent section modulus, W = (E sI s +E c I c ) / (h / 2), where h is the cross-sectional height, I s I c These are the moments of inertia of the steel frame and the concrete section, respectively.

[0015] In this embodiment, more preferably, the additional construction bending moment MΔ is calculated based on a beam model with fixed supports at both ends, MΔ=(6EI·Δ) / L², EI=E s I s +E c I c L is the calculated support length; the total bending moment M = α·P·e0 + (6EI·Δ) / L².

[0016] In this embodiment, more preferably, the crack width w is calculated according to the following formula:

[0017] w=K·(α·e0·P+6EI·Δ / L²)

[0018] Where, K=ψ / (0.87 h0 A) s E s )·(1.9c+0.08d / ρ te ), ψ is the strain non-uniformity coefficient between cracks, h0 is the effective height of the section, c is the thickness of the concrete cover, d is the equivalent diameter of the steel flange, ρ te For effective reinforcement ratio.

[0019] In this embodiment, more preferably, the preset limit value of the crack width is: 0.2 mm in general environment and 0.1 mm in corrosive environment.

[0020] In this embodiment, more preferably, the actual eccentricity e a The bending moment is calculated by back-calculating the strain difference between the upper and lower sections; the set multiple of e0 is 1.2, when e a When the value is greater than 1.2 e0, the additional eccentricity during construction is determined to be significant, and control measures should be taken.

[0021] In this embodiment, more preferably, the step of installing the arc-shaped steel support plate includes: providing an arc-shaped steel support plate with a width greater than the width of the support end face, the two sides of the arc-shaped steel support plate being turned upward to form a grouting cavity, and reserving grouting holes and venting holes; placing the arc-shaped steel support plate between the support end and the diaphragm wall; after the support is in place, injecting micro-expansion high-strength mortar into the grouting cavity through the grouting holes, and forming a gapless rigid connection after curing.

[0022] In this embodiment, more preferably, the strain sensor is a vibrating wire strain gauge or a fiber optic grating sensor, with four measuring points arranged circumferentially in each pre-embedded or installed section for real-time monitoring of axial strain and bending strain.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention provides a prefabricated composite support design and construction control method that considers eccentricity. Through a formula for the influence of centroidal eccentricity during the manufacturing stage, designers can directly calculate the impact of manufacturing errors, improving the safety of support applications. It considers both the initial centroidal eccentricity during manufacturing and quantifies the additional bending moment and cracks caused by diaphragm wall displacement during construction, achieving full-process safety control. Installing a support plate and grouting at the connection between the support and the diaphragm wall eliminates installation gaps, forming a rigid connection, effectively controlling end displacement transmission, reducing the additional bending moment of the support, and improving overall stability. By accurately calculating and replacing empirical amplification factors, cross-sectional design can be optimized, saving 10%~20% of materials; reusability further reduces costs; and real-time monitoring reduces accident risks, resulting in significant economic benefits. Detailed Implementation

[0025] The following detailed description, in conjunction with specific embodiments, provides a prefabricated composite support design and construction control method considering eccentricity, as provided by the present invention. The advantages and features of the present invention will become clearer from the following description.

[0026] The following details the structural composition of the intelligent construction collaborative management and control platform for the entire deep foundation pit construction process of the present invention.

[0027] Example 1

[0028] The following describes a prefabricated combined support design and construction control method considering eccentricity provided by the present invention, with reference to specific embodiments.

[0029] To eliminate the additional impact of eccentricity caused by precast composite supports during construction, this embodiment provides a design and construction control method for precast composite supports that considers centroidal eccentricity during the steel-concrete design stage and displacement eccentricity during the construction stage.

[0030] During the factory fabrication stage: The composite support consists of internal steel sections (H-beams or steel pipes) and an outer reinforced concrete casing. Vibrating wire strain gauges or fiber optic grating sensors are pre-embedded in the middle and ends of each segment, and four measuring points are arranged around each pre-embedded or installed section to monitor axial and bending strain in real time.

[0031] CNC positioning fixtures are used to ensure that the deviation between the centroid of the steel frame and the centroid of the concrete in each segment is ≤ L / 5000, where L is the segment length.

[0032] Before leaving the factory, the e0 value is measured using a 3D laser scan and recorded on the component information plate.

[0033] Design calculation methods for the processing stage:

[0034] The formula for reducing the bearing capacity under manufacturing eccentricity is derived. The precast composite support is considered as a compression member composed of steel and concrete. The initial centroidal eccentricity is set as e0 (measured value, unit: mm). Under axial compressive force P, the steel supports Ps, and the concrete supports Pc, P = Ps + Pc. The axial force distribution coefficient of the steel is defined as α = Ps / P, determined by the stiffness ratio.

[0035] α= (Es As) / (Es As + Ec Ac); (Formula 1)

[0036] Where Es and Ec are the elastic moduli, and As and Ac are the cross-sectional areas.

[0037] Due to the centroidal eccentricity, the force Ps borne by the steel frame and the force Pc borne by the concrete are separated by a distance e0, forming a couple. The resulting additional bending moment is:

[0038] Madd = αP · e0; (Formula 2)

[0039] The combined support, under the combined action of axial force P and additional bending moment Madd, is calculated as an eccentrically compressed member. According to mechanics of materials, the maximum compressive stress at the edge of the section is:

[0040] σmax = P / A + Madd / W (Formula 3)

[0041] In the formula, A = As + Ac, W is the equivalent section modulus, W = I / (h / 2), I = EsIs + EcIc (converted according to stiffness).

[0042] When the steel or concrete reaches its design strength, the structural member reaches its ultimate bearing capacity. Let σmax = f (the design strength of the material, whichever is smaller for steel or concrete), and solve equations 2 and 3 simultaneously to find the ultimate bearing capacity Pmax:

[0043] Pmax = f / [1 / A + (αe0) / W] (Formula 4)

[0044] Compare Pmax with the actual applied axial pressure P to determine whether the bearing capacity is met.

[0045] During the construction phase, the formulas for the additional bending moment and crack width caused by the displacement of the diaphragm wall in this invention are used to determine whether the support meets the requirements.

[0046] Suppose that when the foundation pit is excavated to a certain depth, the horizontal displacement of the diaphragm wall at the support elevation is Δ (unit: mm, which can be measured by inclinometer). The support is fixed to the diaphragm wall at both ends, and the displacement of the diaphragm wall forces the support to bend. Simplifying the support as a beam fixed at both ends, the additional bending moment generated within the beam when the relative displacement Δ occurs at the two supports is:

[0047] M Δ =(6EI·Δ) / L² (Formula 5)

[0048] EI = EsIs + EcIc, where L is the calculated length of the support (distance between the two walls).

[0049] Under the action of axial pressure P, and with the addition of construction-induced bending moment MΔ, the total bending moment is:

[0050] M=Madd+MΔ=αP·e0+(6EI·Δ) / L² (Formula 6)

[0051] According to the concrete structure design code, for eccentrically compressed members, the crack width w can be calculated using the following simplified formula:

[0052] w=ψ·(σs / Es)·(1.9c+0.08d / ρ te ) (Formula 7)

[0053] In the formula:

[0054] ψ is the strain non-uniformity coefficient between cracks, ranging from 0.7 to 1.0;

[0055] σs is the stress in the flange of the steel section in the tension zone, σs=M / (0.87h0As);

[0056] c represents the thickness of the protective layer;

[0057] d is the equivalent diameter of the steel flange;

[0058] ρ te For effective reinforcement ratio.

[0059] Further, the direct relationship between crack width w and axial force P and displacement Δ is derived:

[0060] w=K·(αe0·P+(6EI·Δ) / L²) (Formula 8)

[0061] Where K = ψ / (0.87h0AsEs)·(1.9c + 0.08d / ρ) te ), where is a comprehensive coefficient that can be calculated in advance. Formula 8 shows that the crack width is linearly related to the axial force P and the diaphragm wall displacement Δ, which is convenient for real-time estimation using monitoring data.

[0062] During construction, sensors were deployed. Strain gauges were attached to the steel flanges and concrete surface at both ends and mid-span of each combined support section, with four measuring points (up, down, left, and right) at each section, for a total of 12 measuring points per section. Strain data was collected after each layer was excavated, and the inclination displacement Δ of the diaphragm wall at the corresponding elevation was recorded simultaneously.

[0063] Based on the measured strain ε, the actual stress σ = E·ε is calculated using Hooke's Law. Calculations are performed separately for steel and concrete.

[0064] Safety assessment criteria:

[0065] Compare the measured stress with the stress corresponding to the ultimate bearing capacity calculated by Formula 4, and require σ≤[σ].

[0066] The actual eccentricity e is calculated based on the measured strain. a Compared with the actual measured e0 during manufacturing, if e a A value >1.2e0 indicates significant additional eccentricity during construction, requiring control measures (such as adjusting the excavation sequence or adding temporary supports).

[0067] Calculate the crack width w corresponding to the current P and Δ according to Formula 8, and require w ≤ 0.2 mm (general environment) or w ≤ 0.1 mm (corrosive environment).

[0068] For combined supports that may fail to meet the requirements for cracks and bearing capacity due to eccentricity, an arc-shaped steel support plate is installed between the support end and the diaphragm wall. The arc-shaped steel support plate is closely attached to the pre-embedded steel plate of the diaphragm wall or directly connected to the wall surface.

[0069] The width of the arc-shaped steel support plate is greater than the width of the support end face, and the two sides are turned up to form a grouting cavity, with grouting holes and venting holes reserved in the cavity.

[0070] After the support is hoisted into place, micro-expansion high-strength mortar is injected into the end cavity through the grouting hole to form a rigid connection between the support end and the diaphragm wall without gaps.

[0071] After the grout has cured, the support plate and the mortar work together to transfer axial force and bending moment, effectively eliminating local bending deformation caused by installation gaps or uneven surfaces of the diaphragm wall, while making the stress distribution at the ends more uniform and reducing stress concentration.

[0072] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. The above embodiments only illustrate several implementations of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A design and construction control method considering the eccentricity of a precast reinforced concrete composite support, wherein the precast composite support comprises an internal steel frame and an outer concrete casing, characterized in that, The method includes: Factory processing stage: When prefabricating each segment, strain sensors are pre-embedded in the middle and ends of the segment. CNC positioning fixtures are used to ensure that the deviation between the centroid of the steel frame and the centroid of the concrete of each segment is ≤L / 5000, where L is the segment length. Before leaving the factory, the initial centroid eccentricity e0 is measured and recorded by three-dimensional laser scanning. Design verification stage: The precast composite support is regarded as a compression member composed of steel and concrete. The axial force distribution coefficient α of the steel is determined according to the stiffness ratio. The additional bending moment Madd caused by centroidal eccentricity under the action of axial pressure P is calculated using e0. As an eccentrically compressed member, the ultimate bearing capacity Pmax is calculated based on Madd and P, and the design axial force is not greater than Pmax. Construction monitoring phase: Strain sensors are installed at both ends of the support and at the mid-span section. Strain data of the steel frame and concrete is collected layer by layer as the foundation pit is excavated, and the horizontal displacement Δ of the diaphragm wall at the support elevation is obtained. The additional bending moment M is calculated based on Δ. Δ M Δ The total bending moment M is obtained by superimposing the result with Madd, and the crack width w is calculated from M; simultaneously, the actual eccentricity e during the construction stage is calculated from the measured strain. a , will e a Compare with e0 and check the cross-sectional stress; Construction control phase: When the crack width w exceeds the preset limit, or e a When the stress exceeds the set multiple of e0, or when the measured cross-sectional stress exceeds the stress limit, control measures shall be taken.

2. The method according to claim 1, characterized in that, The control measures include adjusting the excavation sequence, adding temporary supports, and / or installing curved steel support plates between the support ends and the diaphragm wall.

3. The method according to claim 1, characterized in that, The allocation coefficient α is given by the formula α=(E s A s ) / ( E s A s +E c A c The values ​​are determined as follows: Es and Ec are the elastic moduli of steel and concrete, respectively, and As and Ac are the cross-sectional areas of steel and concrete, respectively.

4. The method according to claim 3, characterized in that, The ultimate bearing capacity Pmax is obtained by making the maximum compressive stress at the edge of the section reach the material strength design value f, satisfying the formula Pmax= f / [1 / A + (α·e0) / W ], where A=A s +A c W is the equivalent section modulus, W = (E s I s +E c I c ) / (h / 2), where h is the cross-sectional height, I s I c These are the moments of inertia of the steel frame and the concrete section, respectively.

5. The method according to claim 4, characterized in that, The additional bending moment during construction M Δ Based on the model of a beam with fixed supports at both ends, M is calculated. Δ = (6EI·Δ) / L², EI = E s I s +E c I c L is the calculated support length; the total bending moment M = α·P·e0 + (6EI·Δ) / L².

6. The method according to claim 5, characterized in that, The crack width w is calculated according to the following formula: w=K·(α·e0·P+6EI·Δ / L²) Where, K=ψ / (0.87h0A) s E s )·(1.9c+0.08d / ρ te ), ψ is the strain non-uniformity coefficient between cracks, h0 is the effective height of the section, c is the thickness of the concrete cover, d is the equivalent diameter of the steel flange, ρ te For effective reinforcement ratio.

7. The method according to claim 6, characterized in that, The preset limit for the crack width is: 0.2 mm in general environment and 0.1 mm in corrosive environment.

8. The method according to claim 1, characterized in that, The actual eccentricity e a The bending moment is calculated by back-calculating the strain difference between the upper and lower sections; the set multiple of e0 is 1.2, when e a When the value is greater than 1.2 e0, the additional eccentricity during construction is determined to be significant, and control measures should be taken.

9. The method according to claim 1, characterized in that, The steps for installing the arc-shaped steel support plate include: providing an arc-shaped steel support plate with a width greater than the width of the support end face; forming grouting cavities by flipping the two sides of the arc-shaped steel support plate upwards, and reserving grouting holes and venting holes; placing the arc-shaped steel support plate between the support end and the diaphragm wall; and injecting micro-expansion high-strength mortar into the grouting cavity through the grouting holes after the support is in place, forming a gapless rigid connection after curing.

10. The method according to claim 1, characterized in that, The strain sensor is a vibrating wire strain gauge or a fiber optic grating sensor. Four measuring points are arranged circumferentially in each pre-embedded or installed section for real-time monitoring of axial strain and bending strain.