Mechanical forcible entry construction method for inclined-leg rigid frame bridge

Abstract

The invention relates to the technical field of highway bridge demolition, in particular to a mechanical demolition construction method for a slant leg rigid frame bridge. Through the means of combining on-site actual measurement and numerical simulation analysis, a non-linear refined bridge demolition model is adopted, and the whole construction process of bridge mechanical demolition is reasonably simulated. And performing whole-process finite element analysis and comparison on the to-be-broken bridge to accurately obtain the collapse state of the bridge and the deflection limit value of the collapse of the bridge. Bridge breaking is carried out according to the optimal breaking sequence, and risk early warning can be effectively carried out. According to the technical scheme, on the basis of the scheme, real-time monitoring is further carried out in the whole forcible entry process through a strain sensor and long-distance deflection measuring equipment. And the construction risk of mechanical forcible entry is further reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of highway bridge demolition, and particularly belongs to a mechanical demolition construction method for a skew-leg rigid frame bridge. Background Art

[0002] With the rapid development of the economy, the reconstruction and expansion projects of expressways are carried out in an all-round way. Due to the deficiencies in the early design concept, the overpasses across expressways do not reserve the space required for the reconstruction and expansion of expressways, so they need to be demolished. The bridge mechanical demolition construction technology is a common construction method. However, due to many difficulties such as material nonlinearity, geometric nonlinearity, and boundary nonlinearity in the bridge mechanical demolition construction, it is extremely difficult to simulate the stress state of the whole demolition process through numerical simulation. The skew-leg rigid frame overpass is one of the common types of overpasses across expressways. Compared with conventional simply supported beams and continuous beams, the demolition construction is more difficult and risky.

[0003] At present, the bridge mechanical demolition construction usually adopts empirical methods such as long-arm machinery and on-site experience judgment. However, it is difficult to control the risks in the construction process relying on experience, the requirements for personnel are relatively high, and the reliability is insufficient.

[0004] In recent years, safety accidents caused by bridge demolition construction have occurred from time to time. The construction monitoring in the bridge demolition process often exists in large-span bridge types. For the demolition project of small-span bridges such as overpasses across lines, due to the relatively high cost of existing monitoring technologies, construction monitoring is generally not carried out, which further increases the possibility of safety accidents in the demolition construction.

[0005] At present, the bridge mechanical demolition construction is very rough, often generating a large amount of dust, prone to great risks when the bridge collapses, and the concrete falling is easy to damage the road surface of the overpass highway. Therefore, a fine and reasonable mechanical demolition construction plan is urgently needed. Since the stress of the skew-leg rigid frame bridge is more complex than that of the ordinary simply supported beam bridge, it is more necessary to carry out the simulation analysis of the whole demolition process and construction monitoring, so as to judge the collapse time and collapse state and obtain the optimal demolition method. Summary of the Invention

[0006] The purpose of the present invention is to provide a mechanical demolition construction method for a skew-leg rigid frame overpass across a line to solve the technical problems that it is difficult to predict the bridge collapse result and the construction safety is poor in the mechanical demolition construction process of the existing skew-leg rigid frame overpass across a line.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A mechanical demolition construction method for a skew-leg rigid frame overpass across a line includes the following steps:

[0009] Step 1: Establish a geometric model according to the dimensions of the inclined-leg rigid-frame bridge to be demolished; the geometric model includes concrete constitutive and steel constitutive. Endow the geometric model with an elastoplastic material constitutive model, perform mesh division on the geometric model, and then apply loads and boundaries to complete the model establishment.

[0010] Step 2: Conduct simulation calculation and analysis on different mechanical demolition sequences in the geometric model respectively to determine the optimal mechanical demolition sequence; the mechanical demolition sequences include: the first one starts at a position between 2m and 2.5m from the mid-span at the top of the inclined leg, the second one starts at the mid-span position of the bridge, and the third one starts at the inclined leg position of the bridge; through the simulation calculation and analysis of the three mechanical demolition sequences respectively, obtain the optimal demolition plan.

[0011] Step 3: Demolish the inclined-leg rigid-frame bridge to be demolished according to the mechanical demolition sequence obtained in Step 2. Step 3 also includes setting up on-site monitoring for the whole process of mechanical demolition construction.

[0012] The beneficial effects of this solution are as follows: By combining on-site measurement and numerical simulation analysis, using a non-linear refined bridge demolition model, the whole process of bridge mechanical demolition construction is reasonably simulated. Through the finite element analysis and comparison of the whole process of the bridge to be demolished, the collapse state of the bridge and the deflection limit value of the bridge collapse are accurately obtained. Demolishing the bridge according to the optimal demolition sequence can effectively conduct risk early warning. In the technical solution of the present invention, further on the basis of the above solution, real-time monitoring is carried out throughout the demolition process through strain sensors and long-distance deflection measurement equipment. Further reduce the construction risk of mechanical demolition.

[0013] As a preferred solution of the present invention, in Step 1, the specific implementation method of the geometric model is as follows: 1.1 Use CAD software to establish a three-dimensional geometric model of the inclined-leg rigid-frame bridge, and then import it into the finite element software for steps such as mesh division, boundary condition setting, and load application. In the demolition model of the inclined-leg rigid-frame bridge, concrete is simulated by C3D8R elements, prestressed steel bars are simulated by T3D2 elements, and steel bars are placed in the concrete by the embed command. The boundary conditions are arranged according to the actual situation, and the model change function in ABAQUS software is used to simulate the construction stage.

[0014] Preferably, different material constitutives have a great influence on the result accuracy. Considering the stress characteristics of the structure during the mechanical demolition construction of the inclined-leg rigid-frame bridge, the concrete adopts a damage plasticity constitutive model. Through comparison with the elastic constitutive, elastoplastic constitutive, and smeared crack constitutive models, the results show that the damage plasticity constitutive model has obvious advantages in result accuracy. The steel constitutive adopts a bilinear ideal elastoplastic constitutive.

[0015] Preferably, for the concrete damaged plasticity model, the stress-strain constitutive relation of concrete is selected in accordance with the Code for Design of Concrete Structures (GB 50010-2010), and the damage factor is calculated. For the steel bar constitutive relation, the standard strength value is adopted as the yield strength.

[0016] As a preferred solution of the present invention, the parameters of the concrete plastic damage constitutive model are taken with reference to the Code for Design of Concrete Structures (GB 50010-2010), and the parameters of the concrete plastic damage model are calculated. The steel bar constitutive model adopts an ideal elastic-plastic model, that is, a double-line constitutive model. The stressed steel bars of the main beam and the inclined leg are HRB335, and the yield strength is taken as 335 MPa.

[0017] As a preferred solution of the present invention, in step 1, the grid of the concrete structure adopts C3D8R elements. When meshing the geometric model, the cutting content includes: there is a dividing surface between the cut guardrail and the main beam, there is a dividing surface between the cut bridge deck and the main beam, there is a cutting surface between the flange plate corresponding to the width of the cut guardrail and the main beam, the hollow boundary surface of the cut main beam extends to the solid position of the main beam, there is a corresponding cutting surface between the cut main beam and the inclined leg, there is a cutting surface between the cut inclined leg and the bearing platform, and it is cut into different geometric body sets according to the corresponding demolition sequence; the steel bars adopt T3D2 elements (two-node linear three-dimensional truss elements), and the meshing of the steel bars takes twice the size of the main beam. This setting method can not only ensure the accuracy of the calculation, but also save the calculation amount.

[0018] The grid of the concrete structure adopts C3D8R (8-node hexahedron linear reduced integration element). This element has the advantages of easy convergence and fast calculation speed compared with other types of solid elements (such as C3D8, C3D4, etc.). However, this element requires the cut solid geometric model to be relatively regular. Therefore, it is necessary to regularize the cutting of the geometric model of the inclined leg rigid frame bridge.

[0019] In view of the characteristics of the geometric model of the overpass and the needs of subsequent demolition simulation analysis, the cutting content includes: there is a dividing surface between the cut guardrail and the main beam, there is a dividing surface between the cut bridge deck and the main beam, there is a cutting surface between the flange plate corresponding to the width of the cut guardrail and the main beam, the hollow boundary surface of the cut main beam extends to the solid position of the main beam, there is a corresponding cutting surface between the cut main beam and the inclined leg, there is a cutting surface between the cut inclined leg and the bearing platform, and it is cut into different geometric body sets according to the corresponding demolition sequence.

[0020] As a preferred embodiment of the present invention, in step 1, the applied load only includes the self-weight of the concrete and the self-weight of the steel bars; the applied boundary conditions include: establishing a bearing entity at the position of the bearing of the abutment, and the bearing material is an elastic material according to the vertical stiffness of the bearing; setting a node coupling at the center position of the bottom of the bearing, and setting it as fixed at the coupling node; simulating the contact between the top surface of the bearing and the bottom of the main girder in a hard contact manner; setting the bottom of the abutment as fully fixed; the steel bars and the concrete are simulated by the built-in area method, and the steel bar nodes and the nodes near the concrete deform cooperatively.

[0021] As a preferred embodiment of the present invention, in step 2, it is for the simulation of the construction stage. According to the order of mechanical demolition, the birth and death element method is used to passivate the corresponding positions, so as to simulate the actual demolition process of the inclined leg rigid frame bridge.

[0022] As a preferred embodiment of the present invention, in step 3, before the demolition construction, it also includes construction preparation work, and the preparation work includes the arrival of construction machinery and traffic organization planning.

[0023] Specifically, the construction machinery preparation includes hydraulic breakers, hydraulic excavators, sprinkler trucks, mechanical grabs, dump trucks, and loaders. The hydraulic breaker and the hydraulic excavator work together for the demolition of the main girder; the mechanical grab and the hydraulic excavator work together for the demolition of the billboard; the sprinkler truck is used to reduce the diffusion of dust during the demolition construction; the dump truck is used to transport the concrete after the bridge is broken; the loader is used to load the broken concrete. The construction personnel preparation includes: on-site management personnel, mechanical operators, technical guidance personnel, and safety warning personnel. All personnel need to have the corresponding qualifications. The construction plan includes the content of specific construction techniques, construction processes, technical guarantee conditions, etc. required by the specifications. The traffic organization preparation includes the setting of diversion points, the layout of detour routes, the setting of signboards, etc.

[0024] Complete traffic closure, laying cushion protection, and billboard demolition. The traffic closure should be completed within 3 hours before construction, leaving corresponding time for all vehicles on the highway to clear. For the laying of cushion protection, first cover the road surface within 30 meters longitudinally within the radiation range of the overpass with colored strip cloth, and then cover it with 50 cm thick soil to protect the road surface, and appropriately thicken it to 60 cm thick under the orthographic projection of the bridge. For the demolition of the billboard, a hydraulic excavator and a mechanical grab work together to demolish the billboard.

[0025] In Step 3, the preparatory work further includes setting up on-site monitoring throughout the whole process of mechanical demolition construction. The monitoring setup includes setting up strain sensors and deflection measurement devices. The strain sensors are disposable sensors, which are set at the position with the largest stress change on the inclined-leg rigid-frame bridge. The deflection measurement device is set at the mid-span position, and the deflection monitoring starts during the construction and ends after the bridge collapses.

[0026] Select a position with a relatively large strain change to set up vibrating wire strain sensors. Preferably, sensors that can record strain data in real time are selected. The strain sensors are disposable items, and the sensors will be damaged after the bridge collapses, so disposable sensors with excellent economic benefits can be selected. The sensors can be tightly connected to the concrete with strong glue or anchor bolts. The sensors use wired transmission, and the wire length should exceed 5 times the height of the bridge and should exceed the closed area distance by 5 m.

[0027] Adopt a long-distance deflection measurement device based on images. The device layout position should exceed 5 m outside the construction closed area. The measuring point is at the mid-span position. According to the non-linear finite element simulation calculation results of the bridge demolition construction process and the full-scale local test experience, take 0.8 times of the theoretical calculation result of the deflection as the collapse warning value, and take the sum of the ultimate tensile strain and the initial compressive strain of the concrete as the inclined-leg damage warning value.

[0028] The inclined-leg damage warning value is used to judge the damage through the measurement results of the strain gauges. The calculation formula for the inclined-leg damage warning value is as follows:

[0029]

[0030] In the formula: ε - inclined-leg damage warning value; σ1 - standard value of concrete tensile strength; σ2 - reserve compressive stress of the inclined leg in the completed bridge state; E - elastic modulus of the inclined-leg concrete.

[0031] The demolition position is about 2 m from the mid-span at the top of the inclined leg. This position is the most reasonable position obtained through simulation analysis. Compared with demolishing from other positions (mid-span, inclined leg, etc.), it has the advantages of rapid collapse and vertical collapse.

[0032] The inclined-leg damage warning is a secondary warning, that is, when the reading of the strain sensor exceeds the inclined-leg damage warning value, it indicates that the concrete of the inclined leg has cracked and the bridge is entering the plastic state, and the construction personnel should increase their attention. The main beam deflection warning is a primary warning, that is, when the deflection measurement result is greater than the collapse warning value, the bridge is about to collapse, and the mechanical operator should change the mechanical operation method and chisel by extending the mechanical arm to further ensure their own safety and make the bridge collapse smoothly.

[0033] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0034] In the technical solution of the present invention, by means of on-site measurement and numerical simulation analysis, a non-linear refined bridge demolition model is adopted to reasonably simulate the whole construction process of mechanical bridge demolition. Through the finite element analysis and comparison of the bridge to be demolished throughout the process, the collapse state of the bridge and the deflection limit value of the bridge collapse are accurately obtained. Demolishing the bridge according to the optimal demolition sequence can effectively carry out risk early warning.

[0035] In the technical solution of the present invention, further on the basis of the above solution, real-time monitoring is carried out throughout the demolition process through strain sensors and long-distance deflection measurement equipment. Further reducing the construction risk of mechanical demolition. Description of the Drawings

[0036] Figure 1 is a schematic structural diagram of the bridge to be demolished in Embodiment 1 of the present invention;

[0037] Figure 2 is a construction process diagram of the numerical simulation of the present invention;

[0038] Figure 3 is a simulation diagram of the first demolition sequence in the construction method of the present invention;

[0039] Figure 4 is a simulation diagram of the second demolition sequence in the construction method of the present invention;

[0040] Figure 5 is a simulation diagram of the third demolition sequence in the construction method of the present invention;

[0041] Figure 6 is the strain and deflection monitoring and early warning curve of the inclined leg rigid frame overpass of the present invention.

[0042] Icon: 1 - abutment; 2 - inclined leg; 3 - superstructure; Detailed Embodiments

[0043] In order to more clearly describe the invention purpose, technical solution and technical effect advantages in the specific implementation cases of the present invention, the following will combine the specification drawings of the present invention to elaborate on the solutions in specific embodiments in detail. The specific technical solutions involved in the following specific embodiments are only for clearly and completely describing the innovative technical solutions of the present invention. They are only a part of the specific implementation solutions that the present invention can adopt, not all embodiments, and should not be construed as a limitation to the innovative solutions of the present invention. Any solutions adopting the same inventive concept of the present invention should be included in the protection scope of the present invention.

[0044] Secondly, the relevant descriptions of the drawings in the specific embodiments of the present invention are only for the convenience of those skilled in the art to understand the solution of the present invention. The display of some details in the drawings is for the convenience of clearly presenting the technical solution, and it should not be considered that all the technical features in the drawings must be incorporated into the specific embodiments. Moreover, the detailed features in the drawings should not be regarded as additional limitations on the innovative technical solution of the present invention. The components in each embodiment described and shown in the drawings can be combined and arranged in different configurations, and these variations in combination and arrangement should be regarded as a part of all the embodiments of the innovative solution of the present invention and fall within the scope of protection of the present invention.

[0045] In summary, the solutions or descriptions presented in the specific embodiments and the drawings of the present invention are not intended to limit the scope of protection claimed, but merely represent selected embodiments / cases to assist those skilled in the art in understanding the relevant innovative solutions. Based on these embodiments, all other equivalent or parallel embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection claimed by the present invention.

[0046] It should be noted that, without special instructions, in the description of the specific embodiments of the present invention, the expression terms indicating the orientation or positional relationship such as "upper", "lower", "left", "right", "center", "inner", "outer", etc. are all based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the invention product / device / apparatus is usually used. These terms of orientation or positional relationship are only for the convenience of describing the solution of the present invention or simplifying the description in the specific embodiments to facilitate those skilled in the art to quickly understand the solution, rather than indicating or implying that a specific device / component / element must have a specific orientation or be constructed and operated in a specific positional relationship. Therefore, it should not be construed as a limitation on the present invention.

[0047] In addition, if terms such as "horizontal", "vertical", "hanging", etc. appear, it does not mean that the corresponding device / component / element is required to be absolutely horizontal, vertical or hanging, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and it does not mean that the structure must be completely horizontal, but it can be slightly inclined. Or, it can be simply understood that the corresponding device / component / element is set in a specific direction such as "horizontal", "vertical", "hanging", etc., and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, more preferably within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still play its role in the solution of the present invention.

[0048] In addition, the expressions such as "first", "second", "third", etc. in the terms are only used to distinguish the descriptions of the same or similar components, and should not be understood as emphasizing or implying the relative importance of specific components.

[0049] In addition, in the description of the embodiments of the present invention, "several", "multiple", and "a number of" represent at least 2. It can be any situation such as 3, 4, 5, 6, 7, 8, 9, etc., or even more than 9.

[0050] In addition, in the description of the technical solutions of the present invention, unless otherwise clearly specified / defined / restricted, the terms "set", "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be connection means commonly used in the art such as welding, riveting, bolting, and threaded connection. Such a connection can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two components.

[0051] For those skilled in the art, when understanding the solutions described in the specific embodiments of the present invention, they can refer to the conventional technical manuals in the art. At the same time, for the places where the above terms appear, they can make appropriate understandings or adjustments referentially. Without creative labor, they can derive the implementation situations of the same or similar technical solutions.

[0052] The above embodiments only describe the basic principles, main features, and / or advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and the description in the invention content part of the specification are only the principles or specific cases of the present invention. Without departing from the essence of the innovative idea of the present invention, there are various changes and improvements to the innovative solutions of the present invention, and these changes and improvements all fall within the scope of protection required by the present invention.

[0053] The following will describe the present invention in detail with reference to the accompanying drawings.

[0054] In order to make the purpose, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0055] Embodiment 1

[0056] This embodiment provides a mechanical demolition construction method for a skew-leg rigid-frame bridge, and this method has been practiced in the reconstruction and expansion project of an overpass on a certain expressway, as Figure 1The figure shows a structural schematic diagram of the bridge to be demolished; its superstructure 3 is in the form of a (14 + 28 + 14)m reinforced concrete inclined-leg rigid frame. The bridge width is 5.5m, (0.5m guardrail width + 4.5m deck clear width + 0.5m guardrail width). The abutment 1 is a U-shaped abutment, and the inclined leg 2 adopts an enlarged foundation, which is orthogonal to the lower-crossing expressway at 90°.

[0057] Specifically, the technical solution of the present invention includes the following steps:

[0058] Step 1: Establish a geometric model according to the dimensions of the inclined-leg rigid frame bridge to be demolished; the geometric model includes a concrete constitutive model and a steel bar constitutive model. Endow the geometric model with an elastoplastic material constitutive model, and after meshing the geometric model, apply loads and boundaries to complete the model establishment.

[0059] The specific method for establishing the geometric model is as follows:

[0060] 1.1 Establish the geometric model of the inclined-leg rigid frame: In this embodiment, refer to the drawings of the target structure to be demolished, the inclined-leg rigid frame bridge, and combine the on-site measured dimensions to establish the geometric model; and according to the drawings, establish the geometric model of the steel bars. According to the modeling analysis experience and result comparison analysis, to simplify the calculation, the influence of stirrups can be ignored, and only the longitudinal stressed steel bars are established.

[0061] 1.2 Endow the elastoplastic material constitutive model: Different material constitutive models have a great influence on the result accuracy. Combining the stress characteristics of the structure during the mechanical demolition construction process of the inclined-leg rigid frame bridge, it can be known from the design drawings that the concrete strength grade of the main girder is C40, and the concrete strength grades of the inclined legs and the foundation are C25.

[0062] The constitutive parameters of the concrete damage plasticity model are shown in Tables 1 and 2 below;

[0063] Table 1 is the parameter table of the concrete CDP constitutive model

[0064]

[0065] Table 2 is the parameter table of stress, strain and damage factor of the concrete CDP constitutive model

[0066]

[0067]

[0068] The process of overpass demolition has strong material nonlinearity, that is, extensive concrete damage occurs during the collapse of the overpass. The basic assumption of the concrete plastic damage model is that the isotropic compressive behavior and tensile behavior lead to material damage and cracking failure. This model is applicable to both implicit and explicit dynamic analyses, and can display the inelastic cracking failure behavior of concrete materials with different strength grades in post-processing. It can better simulate the mechanical behavior of concrete in the simulation analysis of overpass mechanical demolition. Through comparison with elastic constitutive, elastoplastic constitutive, and smeared cracking constitutive models, the results show that the damage plasticity constitutive model has obvious advantages in terms of result accuracy.

[0069] The steel bar constitutive used is a bilinear ideal elastoplastic constitutive. The stressed steel bars of the main girder and inclined legs of this bridge are HRB335, with a yield strength of 335 MPa and an elastic modulus of 200000 MPa.

[0070] For the concrete damage plasticity model, the concrete stress-strain constitutive is selected in accordance with the "Code for Design of Concrete Structures" (GB 50010-2010) to calculate the damage factor. For the steel bar constitutive, the strength standard value is used as the yield strength.

[0071] 1.3. Mesh division: The mesh of the concrete structure uses C3D8R (8-node hexahedron linear reduced integration element). This element has advantages such as easy convergence and fast calculation speed compared to other types of solid elements (such as C3D8, C3D4, etc.). However, this element requires the cut solid geometric model to be relatively regular. Therefore, it is necessary to regularize the cut of the geometric model of the inclined leg rigid frame bridge.

[0072] According to the characteristics of the geometric model of the overpass across the line and the needs of subsequent demolition simulation analysis, the cutting content includes: there is a dividing surface between the guardrail and the main girder after cutting, there is a dividing surface between the bridge deck and the main girder after cutting, there is a cutting surface corresponding to the width of the guardrail between the flange plate and the main girder after cutting, the hollow boundary surface of the main girder after cutting extends to the solid position of the main girder, there is a corresponding cutting surface between the main girder and the inclined leg after cutting, there is a cutting surface between the inclined leg and the bearing platform after cutting, and it is cut into different geometric body sets according to the corresponding demolition sequence.

[0073] The steel bars use T3D2 (two-node linear three-dimensional truss element) units, and the mesh division of the steel bars takes twice the size of the main girder. This setting method can not only ensure the calculation accuracy but also save the calculation amount.

[0074] 1.4 Applied Loads and Boundaries: Only the self-weight of the structure needs to be considered during the analysis process, and the applied loads are only the self-weight (including the self-weight of concrete and steel bars). To ensure the rationality of the simulation and appropriately simplify the complexity of the model. The applied boundary conditions include: establishing a support entity at the position of the bearing on the abutment, and the support material is an elastic material according to the vertical stiffness of the bearing; setting a node coupling at the center position of the bottom of the bearing, and setting it as fixed at the coupled nodes; simulating the contact between the top surface of the bearing and the bottom of the main beam in a hard contact manner; setting the bottom of the abutment as fully fixed. The steel bars and concrete are simulated by using the built-in region method, that is, the steel bar nodes and the nodes near the concrete deform coordinately.

[0075] Step 2: Conduct simulation calculation and analysis on different mechanical demolition sequences in the geometric model respectively to determine the optimal mechanical demolition sequence; the mechanical demolition sequences include: the first one starts at a position between 2m - 2.5m from the mid-span at the top of the inclined leg, the second one starts at the mid-span position of the bridge, and the third one starts at the inclined leg position of the bridge; through the simulation calculation and analysis of the three mechanical demolition sequences respectively, obtain the optimal demolition plan;

[0076] Use the model change function in the ABAQUS software to simulate the construction stage. Specifically, according to the sequence of mechanically demolishing the concrete, use the birth and death element method to deactivate the corresponding positions, so as to simulate the actual demolition process of the inclined leg steel structure overpass. Specifically, as Figure 2 shown is the construction process diagram of the numerical simulation.

[0077] Based on the construction operability, select three feasible mechanical demolition positions: the first one is at a position about 2m from the mid-span at the top of the inclined leg, as Figure 3 shown; the second one starts mechanical demolition from the mid-span position, as Figure 4 shown; the third one conducts mechanical demolition at the inclined leg position, as Figure 5 shown.

[0078] By comparing Figure 3 and Figure 4 it can be found that the demolition method at a position about 2m from the mid-span at the top of the inclined leg has the advantages of rapid collapse and vertical collapse compared with the methods of starting mechanical demolition from the mid-span position and conducting mechanical demolition at the inclined leg position. Therefore, according to the simulation results, the demolition method at a position about 2m from the mid-span at the top of the inclined leg should be adopted.

[0079] As Figure 3 shown is the simulation diagram of the collapse state of the inclined leg rigid frame overpass when demolishing the main beam at the top of the inclined leg. The main beam collapses vertically and collapses vertically at the demolition part. The whole bridge collapse process has no lateral deviation in the transverse direction of the bridge, the collapse during the whole demolition process is controllable, and the construction risk is low. The area of chiseled concrete only needs to be >50cm 2, compared with the demolition plan at the mid-span of the main girder, the lever arm on one side of the main girder in this plan is longer, which can ensure a smooth collapse.

[0080] From Figure 4 The simulation diagram of the demolition and collapse state of the main girder at the mid-span shows that when the demolition length at the mid-span < 1.6 m (0.1 - 1.6 m), the mid-span deflection is 30 cm, but the main girder does not continue to deflect downward, that is, the overpass does not collapse. It can be analyzed that after the main girder is demolished at the mid-span position, due to the friction between the steel bars and the section contact, a stable system is formed between the two, and both the main girder and the root of the inclined leg are damaged, but it does not completely collapse. To ensure the smooth collapse of the overpass, the demolition length at the mid-span position should > 1.6 m to ensure sufficient displacement space, but a demolition length of 1.6 m will extend the construction period and increase the cost.

[0081] As Figure 5 shown in the simulation diagram of the demolition and collapse state at the middle of the inclined leg, due to the existence of steel bars, the main girder collapses as a whole in the vertical and longitudinal directions to the damaged side of the inclined leg, and there is a lateral deviation in the cross-bridge direction. Such a collapse poses a greater safety risk to construction workers and machinery, and the calculated birth and death element method is for the demolition of an ideal flat section. In the actual construction process, due to the uncontrollability of mechanical demolition, the possibility of lateral deviation in the cross-bridge direction is greater and the risk is greater.

[0082] It can be compared from the above three demolition schemes in sequence that Figure 3 the scheme of demolishing the main girder at the top of the inclined leg in Figure 3 is the best scheme, and the collapse process is controllable. Therefore, according to

[0083] Specifically, as Figure 6 shown in the deformation curve during the mechanical demolition and collapse process of the inclined leg rigid frame overpass, there is a vertical deflection during the collapse process of the inclined leg rigid frame overpass, and due to the asymmetric construction of the demolition in this embodiment, there is also a large deformation in the longitudinal direction of the bridge. The measured vertical deflection at the mid-span of the inclined leg rigid frame overpass within 1300 s after the start of demolition is basically consistent with the simulation analysis results; the difference between the simulation analysis results and the measured results of the vertical deflection at the mid-span of the inclined leg rigid frame overpass gradually increases from 1300 s to 3400 s after the start of demolition; the vertical deflection at the mid-span obtained by simulation analysis is about 7 mm larger than the measured result before the rapid collapse of the inclined leg rigid frame overpass; the reduction coefficient of the simulation analysis result is about 0.81, which can be basically consistent with the measured result.

[0084] It can be analyzed that during the mechanical demolition construction process of the overpass, the concrete is vibrated and broken by the hydraulic breaker. The birth and death element method cannot accurately simulate the actual situation, and the local stiffness degradation caused by the damage and fragmentation of the concrete has a greater impact on the longitudinal deformation of the overpass. Since the vertical deflection is mainly determined by the self-weight and the change of the overall stiffness after damage, the local damage and fragmentation of the concrete have a smaller impact on the vertical deflection of the overpass.

[0085] When conducting the mechanical demolition construction calculation of the overpass, a refined three-dimensional elastoplastic model should be adopted, considering the nonlinear effects. According to the above analysis, the collapse warning value of the overpass should refer to the vertical deflection, and can be calculated as the measured value × reduction coefficient. The reduction coefficient is recommended to be taken as 0.81.

[0086] Analysis shows that the actual collapse process of the overpass involves strong nonlinearity, and the elastoplastic finite element analysis of the overpass at the present stage cannot fully simulate the true collapse state of the overpass. In the early stage of mechanical demolition construction, the nonlinear phenomenon of the structure is not obvious, and the simulation analysis results are basically consistent with the measured results.

[0087] Step 3: Demolish the inclined-leg rigid-frame bridge to be demolished according to the mechanical demolition sequence obtained in Step 2. Step 3 also includes setting up on-site monitoring throughout the mechanical demolition construction process.

[0088] Specifically, in Step 3, before officially conducting the demolition construction, it includes:

[0089] 3.1 Preparation work. The preparation work includes construction machinery and traffic organization. The preparation of the construction machinery includes hydraulic breakers, hydraulic excavators, sprinkler trucks, mechanical grabs, dump trucks, and loaders. The hydraulic breaker and the hydraulic excavator cooperate for the demolition of the main girder; the mechanical grab and the hydraulic excavator cooperate for the removal of the billboard; the sprinkler truck is used to reduce the spread of dust during the demolition construction; the dump truck is used to transport the concrete after the bridge is broken; the loader is used to load the broken concrete. The traffic organization includes the setting of diversion points, the layout of detour routes, the setting of signboards, etc.

[0090] 3.2: Complete traffic closure, lay cushion protection, and remove the billboard. The traffic closure should be completed within 3 hours before the construction, leaving corresponding time for all vehicles on the highway to clear. For the laying of cushion protection, first cover the road surface within 30 meters longitudinally within the radiation range of the overpass with colored strip cloth, and then cover it with 50 cm thick soil to protect the road surface, and appropriately thicken it to 60 cm thick in the orthographic projection under the bridge. For the removal of the billboard, the hydraulic excavator and the mechanical grab work together to remove the billboard.

[0091] According to the optimal demolition position in Step 2, conduct the demolition construction, where the beams, slabs, inclined legs, and foundations are broken and the steel bars are cut. Continue to use the hydraulic breaker and the hydraulic excavator to work together to break the main girder, inclined legs, and foundations. Use a cutting machine to cut the steel bars. Mechanically demolish until the overpass of the overcrossing inclined-leg rigid-frame bridge collapses. The demolition position is about 2 m from the mid-span at the top of the inclined leg.

[0092] Transport the crushed garbage and gradually resume traffic. Use a forklift in cooperation with manual labor to load the crushed garbage onto a dump truck and transport it to the treatment plant. After the garbage is processed, gradually resume traffic.

[0093] Furthermore, step 3.1 also includes setting up on-site monitoring for the whole process of mechanical demolition construction. Specifically, 3.11. Select positions with large strain changes to set up vibrating wire strain sensors.

[0094] Preferably, select sensors that can record strain data in real time. The strain sensor is a disposable item and will be damaged after the bridge collapses, so a disposable sensor with excellent economic benefits can be selected. The said sensor can be tightly connected to the concrete using strong glue or anchor bolts. The sensor uses wired transmission, and the wire length should exceed 5 times the height of the bridge and should also exceed 5 m from the closed area.

[0095] 3.12. Use a long-distance deflection measurement device based on images. The device should be arranged more than 5 m outside the construction closed area, and the measuring point is at the mid-span position. Start monitoring the deflection from the beginning of construction until the end of the bridge collapse.

[0096] 3.13. According to the results of the simulation calculation of the construction process at the time of collapse, take 0.8 times the theoretical calculation result of the deflection as the collapse early warning value, and take the sum of the ultimate tensile strain and the initial compressive strain of the concrete as the inclined leg damage early warning value.

[0097] The damage of the inclined leg is judged by the measurement result of the strain gauge for the said inclined leg damage early warning value. The calculation formula for the said inclined leg damage early warning value is as follows:

[0098]

[0099] In the formula: ε - inclined leg damage early warning value; σ1 - standard value of concrete tensile strength; σ2 - reserve compressive stress of the inclined leg in the completed bridge state; E - elastic modulus of the inclined leg concrete.

[0100] The damage warning of the inclined leg is a secondary warning, that is, when the reading of the strain sensor exceeds the inclined leg damage early warning value, it indicates that the concrete of the inclined leg has cracked and the bridge is entering the plastic state, and the construction personnel should increase their attention. The deflection warning of the main beam is a primary warning, that is, when the deflection measurement result is greater than the collapse early warning value, the bridge is about to collapse, and the mechanical operator should change the mechanical operation method and chisel by extending the mechanical arm to further ensure their own safety and make the bridge collapse smoothly.

[0101] In this embodiment, the standard value of the tensile strength of the concrete is calculated as σ1 = 1.78 MPa; the reserve compressive stress of the inclined leg in the completed bridge state is σ2 = 0.58 MPa; the elastic modulus E of the inclined leg concrete is 28,000 MPa, and the damage warning value ε of the inclined leg is calculated as 84.3 με. The monitoring results are shown in Figure 6 left.

[0102] The deflection warning of the main girder described above is a first-level warning, that is, when the measured deflection result is greater than the collapse warning value, the bridge is about to collapse. The theoretical value of the mid-span deflection at the time of collapse obtained by finite element deduction is 33.4 mm, and 0.8×33.4 = 26.7 mm is taken. The monitoring results are shown in Figure 6 right. The mechanical operator should change the mechanical operation method and carry out the chiseling by extending the mechanical arm to further ensure his own safety and make the bridge collapse smoothly.

[0103] Embodiment 2

[0104] The bridge to be demolished is an overpass across a highway. The bridge is a steel structure with inclined legs. The span is (14 + 28 + 14) m, and the bridge width layout is: 0.5 m (guardrail) + 6.5 m (net width of the bridge deck) + 0.5 m (guardrail) = 5.5 m. U-shaped abutment and enlarged foundation of the inclined leg, orthogonal at 90°. Except that the net width of the bridge deck is different from that in Embodiment 1, the other situations in Embodiment 2 are the same. And the implementation methods are the same as those in Embodiment 1. Through further verification, it is found that by adopting Figure 3 the order of demolition, the final collapse position of the bridge matches the simulation result.

[0105] Comparative Example 1

[0106] The bridge to be demolished is an overpass across a highway. The bridge is a steel structure with inclined legs. The span is (12 + 20 + 12) m, and the bridge width layout is: 0.5 m (guardrail) + 6.5 m (net width of the bridge deck) + 0.5 m (guardrail) = 5.5 m. U-shaped abutment and enlarged foundation of the inclined leg, orthogonal at 90°. Since no simulation deduction was carried out, the mechanical breaker first impacted the root of the inclined leg, but due to the large initial compressive stress in the inclined leg, the breaking was difficult. During the actual demolition process, the whole bridge shifted 5 m to one side, with a relatively high safety risk and difficult construction.

[0107] In summary, the technical solution of the present invention combines on-site measurement and numerical simulation analysis, adopts a non-linear refined bridge demolition model, and reasonably simulates the whole construction process of bridge mechanical demolition. Through the finite element analysis and comparison of the whole process of the bridge to be demolished, the collapse state of the bridge and the deflection limit value of the bridge collapse are accurately obtained. Demolishing the bridge according to the best demolition order can effectively carry out risk warning. In the technical solution of the present invention, further on the basis of the above solution, real-time monitoring is carried out throughout the demolition process through strain sensors and long-distance deflection measurement devices. Further reducing the construction risk of mechanical demolition.

[0108] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A mechanical demolition construction method for a slanted-leg rigid frame bridge, characterized in that: The steps include: Step 1: Establish a geometric model according to the size of the oblique-leg rigid frame bridge to be demolished; the geometric model includes a concrete constitutive model and a steel bar constitutive model, and an elastic-plastic material constitutive model is assigned to the geometric model. After meshing the geometric model, loads and boundaries are applied, and the model establishment is completed; Step 2: In the geometric model, different mechanical demolition sequences are simulated and calculated to determine the best mechanical demolition sequence; the mechanical demolition sequence includes: the first one is to start at a position between 2m and 2.5m from the top of the inclined leg to the middle of the span, the second one is to start at the middle of the span of the bridge, and the third one is to start at the position of the inclined leg of the bridge; the best demolition plan is obtained by simulating and calculating the three mechanical demolition sequences respectively; Step 3: Perform demolition construction on the oblique-legged rigid frame bridge to be demolished according to the mechanical demolition sequence obtained in step 2. Step 3 also includes setting up on-site monitoring of the entire mechanical demolition construction process.

2. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 1 is characterized in that: In step 1, the mesh of the concrete structure adopts C3D8R. When the geometric model is meshed, the cutting contents include: there is a dividing surface between the guardrail and the main beam after cutting, there is a dividing surface between the bridge deck and the main beam after cutting, there is a cutting surface between the flange plate corresponding to the width of the guardrail and the main beam after cutting, the hollow boundary surface of the main beam extends to the solid position of the main beam after cutting, there is a corresponding cutting surface between the main beam and the inclined legs after cutting, there is a cutting surface between the inclined legs and the pedestal after cutting, and it is cut into different geometric body sets according to the corresponding breaking order; T3D2 is adopted for the steel bars, and the mesh division of the steel bars is twice the size of the main beam.

3. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 2 is characterized in that: In step 1, the applied load only includes the deadweight of concrete and steel bars; the applied boundary conditions include: establishing a support entity at the position of the abutment, and using elastic material as the support material according to the vertical stiffness of the support; setting node coupling at the center of the bottom of the support, and setting it to fixed at the coupling node; using hard contact to simulate the top surface of the support and the bottom of the main beam; setting full consolidation at the bottom of the abutment; using a built-in area to simulate the relationship between the steel bars and the concrete, and cooperative deformation between the steel bar nodes and the nodes near the concrete.

4. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 1 is characterized in that: In step 2, according to the order of mechanical demolition, the birth-death unit method is used to passivate the corresponding positions, thereby simulating the actual demolition process of the inclined-leg rigid frame bridge.

5. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 1 is characterized in that: In step 3, before the demolition work is carried out, construction preparation work is also included, and the preparation work includes the arrival of construction machinery and traffic organization planning.

6. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 1 is characterized in that: In step 3, the monitoring setting includes setting a strain sensor and a deflection measuring device. The strain sensor is a disposable sensor. The strain sensor is set at the position where the stress change is the largest on the inclined leg rigid frame bridge. The deflection measuring device is set at the mid-span position. The deflection monitoring starts at the construction and ends after the bridge collapses.

7. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 5 is characterized in that: According to the results of collapse calculation during the construction process simulation, 0.8 times of the theoretical calculation result of deflection was taken as the collapse warning value, and the sum of the ultimate tensile strain and initial compressive strain of concrete was taken as the inclined leg damage warning value.

8. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 5 is characterized in that: The deflection leg injury warning value is used to determine the damage through the strain gauge measurement result. The deflection leg injury warning value calculation formula is as follows: Where: ε-slant leg damage warning value; σ1-concrete tensile strength standard value; σ2-slant leg reserve compressive stress in the bridge state; E-slant leg concrete elastic modulus.

9. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 7 is characterized in that: The slanted leg damage warning is a second-level warning. When the strain sensor reading exceeds the slanted leg damage warning value, it indicates that the concrete of the slanted leg has cracked and the bridge is entering a plastic state. The main beam deflection warning is a first-level warning. When the deflection measurement result is greater than the collapse warning value, the bridge is about to collapse. The bridge can be chiseled out by extending the mechanical arm to make it collapse smoothly.

10. The mechanical demolition construction method of the inclined-legged rigid frame bridge according to claim 7 is characterized in that: In step 3, according to the best demolition position in step 2, demolition construction is carried out; the beams, slanted legs and foundations are crushed, and the steel bars are cut; a hydraulic breaker and a hydraulic excavator work together to crush the main beams, slanted legs and foundations, and a cutting machine is used to cut the steel bars. Mechanical demolition is carried out until the cross-line slanted leg rigid frame bridge collapses.

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