A performance evaluation method for masonry structures near foundation pits

Abstract

A method for evaluating the performance of a masonry structure near a foundation pit comprises: calculating a surrounding ground settlement model δ(x, y) during the foundation pit construction process; calculating the stress σ of each wall of the masonry structure; i ; Calculate the compressive strength excess rate δ c =nc ，j / n j , crack strength excess rate δ t =n t，j / n j ; The performance status of the masonry structure is determined according to the excess rate of compressive strength and the excess rate of cracking strength. The present application provides a method for evaluating the performance of a masonry structure near a foundation pit, which can accurately evaluate the structural performance status of a masonry building under the uneven settlement of the foundation caused by foundation pit excavation.

Description

Technical Field

[0001] The invention belongs to the field of foundation pit support, and in particular relates to a method for evaluating the performance of a masonry structure adjacent to a foundation pit. Background Art

[0002] In the process of urban construction and renovation, the problem of surrounding surface settlement caused by foundation pit excavation has attracted more and more attention. Excessive surface settlement will directly lead to the destruction of surrounding buildings and other structures, resulting in serious consequences. There are many research results on the prediction of surface settlement around foundation pits. The results can be divided into three categories: ① empirical estimation method; ② theoretical analysis method; ③ numerical calculation method. Regarding the impact of foundation pit excavation on adjacent buildings (structures), domestic and foreign scholars have conducted certain research on this. For example, by using model tests and numerical calculation methods, the impact of foundation pit excavation on the surrounding existing masonry structures was studied and analyzed; considering the bearing capacity of the building itself, the finite element calculation method was used for analysis, and the foundation pit deformation control standard based on the bearing capacity of the surrounding buildings was proposed. However, the above analysis method is difficult to quantitatively analyze the performance of building structures, especially the multi-level structural performance of masonry structures cannot be quantitatively analyzed, which makes it difficult to directly apply the analysis results to engineering. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes a method for evaluating the performance of a masonry structure adjacent to a foundation pit, so as to accurately and quantitatively analyze the multi-level structural performance of the masonry structure.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] The present invention provides a method for evaluating the performance of a masonry structure adjacent to a foundation pit, comprising the following steps:

[0006] S1: Establish a three-dimensional finite element model of the foundation pit support and surrounding buildings, and calculate the surrounding ground settlement model δ(x, y) during the foundation pit construction process;

[0007] S2: Establish a refined finite element model of the masonry structure, input the ground settlement model δ(x,y) into the model, and calculate the stress σi of each wall of the masonry structure;

[0008] S3: Taking a single wall j as a unit, the failure distribution of the wall's compressive and tensile strengths, as well as the compressive strength exceeding rate δc,j and the cracking strength exceeding rate δt,j are calculated according to the stress σi of each wall;

[0009] S4: Determine the performance status of the masonry structure based on the compressive strength excess rate δc,j and the crack strength excess rate δt,j.

[0010] As a further improvement of the present invention, the step S1 specifically includes:

[0011] S11: The Mohr-Coulomb model is used to simulate the soil, the plate element is used to simulate the vertical support structure of the foundation pit, and the beam element is used to simulate the foundation pit columns, column piles, supports, cap beams and connecting beams;

[0012] S12: Contact elements are used to simulate the vertical support structure of the foundation pit and the surrounding soil, the foundation pit column piles and the surrounding soil, and the building pile foundation and the surrounding soil.

[0013] S13: The birth-death unit method is used to simulate soil excavation, the construction and demolition of the vertical support structure of the foundation pit, the foundation pit columns, column piles, supports, cap beams, and connecting beams, and the surrounding ground settlement model δ(x, y) during the foundation pit excavation process is obtained.

[0014] As a further improvement of the present invention, the vertical support structure of the foundation pit includes a ground-connected wall and a row of piles.

[0015] As a further improvement of the present invention, the step S2 specifically includes:

[0016] S21: Shell units are used to simulate masonry walls, and hinged supports are used to simulate foundation settlement. The hinged supports are arranged below the wall units, and the spacing between the supports is not less than 1.0m;

[0017] S22: According to the plane coordinates (x i ,y i ), substitute into the surrounding ground settlement model δ(x,y), and obtain the settlement of each hinge support δ(xi,yi);

[0018] S23: Substitute the settlement δ(xi,yi) of each hinge support into the refined finite element model of the masonry structure and calculate the stress σi of each unit of the masonry structure.

[0019] As a further improvement of the present invention, step S3 specifically includes:

[0020] S31: Count the number of wall elements nj, the number of elements nc,j1 that exceed the material compressive strength σc when the element stress is compressive stress, and the number of elements nt,j1 that exceed the material tensile strength σt when the element stress is tensile stress;

[0021] S32: Calculate and obtain the initial value of the compressive strength excess rate δc,j1=nc,j1 / nj1 and the crack strength excess rate δt,j1=nt,j1 / nj1;

[0022] S33: Using the birth-death unit method, after simulating the failure state of the wall unit in which the unit stress is compressive stress and tensile stress and exceeds the material compressive strength σc and tensile strength σt, the compressive strength exceeding rate δc,j2 and the cracking strength exceeding rate δt,j2 of the wall j are calculated again;

[0023] S34: Repeat step S33 to calculate the compressive strength exceeding limit rate δc,ji and the cracking strength exceeding limit rate δt,ji of the wall j for the i-th time.

[0024] As a further improvement of the present invention, step S4 specifically includes:

[0025] S41: When δt,j≥20% or δc,j≥5%, the structural performance state is directly judged as damaged;

[0026] S42: In other cases, according to the compressive strength exceeding limit rate δc,ji and the cracking strength exceeding limit rate δt,ji, the difference values ​​Δδc,j(i,i-1) and Δδt,j(i,i-1) between two adjacent calculation results are obtained;

[0027] S43: Compare the interpolation values ​​of the compressive strength excess rate Δδc,j(i,i-1) and the difference values ​​of the crack strength excess rate Δδt,j(i,i-1). When Δδc,j(i,i-1) and Δδt,j(i,i-1) increase successively, it is judged as destruction. When they decrease successively and do not meet the conditions of S41, it is judged as safe.

[0028] S44: When other situations occur, it is judged as a warning.

[0029] The present application provides a method for evaluating the performance of a masonry structure near a foundation pit, including: calculating the surrounding ground settlement model δ(x, y) during the foundation pit construction process; calculating the stress σi of each wall of the masonry structure; calculating the compressive strength excess rate Crack strength exceeding limit rate The performance status of the masonry structure is determined according to the excess rate of compressive strength and the excess rate of cracking strength. The present application provides a method for evaluating the performance of a masonry structure near a foundation pit, which can accurately evaluate the structural performance status of a masonry building under the uneven foundation settlement caused by foundation pit excavation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart of a method for evaluating the performance of a masonry structure adjacent to a foundation pit provided in an embodiment of the present application;

[0031] Figure 2 A three-dimensional finite element model of the foundation pit support and surrounding buildings in an embodiment of the present invention;

[0032] Figure 3 A cloud map of ground settlement at the section where the masonry building is located in an embodiment of the present invention;

[0033] Figure 4 A ground settlement curve diagram at the location of the masonry building in an embodiment of the present invention;

[0034] Figure 5 A refined finite element model of the masonry structure in an embodiment of the present invention;

[0035] Figure 6 A wall stress cloud diagram of a masonry structure in an embodiment of the present invention;

[0036] Figure 7 A scatter plot of the relationship between the crack resistance excess rate, the compressive strength excess rate and the differential settlement of the building in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solution of the present application, the technical solution in the embodiment of the present application will be clearly and completely described below in conjunction with the drawings in the present embodiment. Obviously, the described embodiment is only a part of the embodiment of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work should belong to the scope of protection of the present application.

[0038] See also Figures 1 to 7 , a flow chart of a method for evaluating the performance of a masonry structure adjacent to a foundation pit provided by the present invention, comprising:

[0039] S1: Establish a three-dimensional finite element model of the foundation pit support and surrounding buildings, and calculate the surrounding ground settlement model δ(x, y) during the foundation pit construction process;

[0040] S2: Establish a refined finite element model of the masonry structure, input the ground settlement model δ(x,y) into the model, and calculate the stress σi of each unit of the masonry structure;

[0041] S3: Taking a single wall j as a unit, calculate the compressive strength excess rate δc and the cracking strength excess rate δt;

[0042] S4: Determine the performance status of the masonry structure based on the compressive strength exceeding rate and the cracking strength exceeding rate.

[0043] In this embodiment, the three-dimensional finite element model of the foundation pit support and the surrounding buildings is established in step S1, and the surrounding ground settlement model δ(x, y) during the foundation pit construction is calculated, which specifically includes:

[0044] S11: The Mohr-Coulomb model is used to simulate the soil, the vertical support structure of the foundation pit (ground-connected wall, pile row) is simulated by plate unit, the foundation pit columns, column piles, supports, cap beams, connecting beams, etc. are simulated by beam units, the surrounding buildings are simulated by solid units, and the building pile foundations are simulated by pile units;

[0045] S12: Contact elements are used to simulate the vertical support structure of the foundation pit and the surrounding soil, the foundation pit column piles and the surrounding soil, and the building pile foundation and the surrounding soil.

[0046] S13: The life-death unit method is used to simulate soil excavation, the construction and demolition of the vertical support structure of the foundation pit (ground-connected wall, pile row), foundation pit columns, column piles, supports, cap beams, and connecting beams, and the surrounding ground settlement model δ(x, y) during the foundation pit excavation process is obtained.

[0047] In this embodiment, the step 2 of establishing a refined finite element model of the masonry structure, inputting the ground settlement model δ(x, y) into the model, and calculating each unit stress σi of the masonry structure specifically includes:

[0048] S21: Shell units are used to simulate masonry walls, and hinged supports are used to simulate foundation settlement. The hinged supports are arranged below the wall units, and the spacing between the supports is not less than 1.0m;

[0049] S22: According to the plane coordinates (x i ,y i ), substitute into the surrounding ground settlement model δ(x,y), and obtain the settlement of each hinge support δ(xi,yi);

[0050] S23: Substitute the settlement δ(xi,yi) of each hinge support into the refined finite element model of the masonry structure and calculate the stress σi of each unit of the masonry structure.

[0051] In this embodiment, the compressive strength exceeding limit rate δc and the cracking strength exceeding limit rate δt described in step 3 specifically include:

[0052] S31: Count the number of wall elements nj, the number of elements nc,j that exceed the material compressive strength σc when the element stress is compressive stress, and the number of elements nt,j that exceed the material tensile strength σt when the element stress is tensile stress;

[0053] S32: Calculate and obtain the compressive strength excess rate δc=nc,j / nj and the crack strength excess rate δt=nt,j / nj.

[0054] In this embodiment, the step 4 of determining the performance status of the masonry structure according to the compressive strength exceeding limit rate and the cracking strength exceeding limit rate respectively includes:

[0055] S41: When δt,j≥20% or δc,j≥5%, the structural performance state is directly judged as damaged;

[0056] S42: In other cases, according to the compressive strength exceeding limit rate δc,ji and the cracking strength exceeding limit rate δt,ji, the difference values ​​Δδc,j(i,i-1) and Δδt,j(i,i-1) between two adjacent calculation results are obtained;

[0057] S43: Compare the interpolation values ​​of the compressive strength excess rate Δδc,j(i,i-1) and the difference values ​​of the crack strength excess rate Δδt,j(i,i-1). When Δδc,j(i,i-1) and Δδt,j(i,i-1) increase successively, it is judged as destruction. When they decrease successively and do not meet the conditions of S41, it is judged as safe.

[0058] S44: When other situations occur, it is judged as a warning.

[0059] In a specific application scenario of the present application, the performance evaluation of the masonry building structure near the foundation pit of the shield working shaft of the Nanjing Jianning West Road Cross-River Tunnel is taken as an example to illustrate the specific implementation process of the present invention:

[0060] 1) In this embodiment, a three-dimensional finite element model can be used to establish a three-dimensional model of the working pit and surrounding buildings, simulate the construction process of underground continuous wall construction, erection of foundation pit support, foundation pit excavation, etc., and obtain the deformation law of surrounding buildings and strata, such as Figure 2 shown.

[0061] 2) Calculate the ground settlement distribution diagram under the condition of excavation from the foundation pit to the bottom of the pit, and obtain the ground settlement curve of the area where the masonry building structure is located, such as Figure 3 and Figure 4 shown.

[0062] 3) Establish a detailed finite element model of the masonry building structure near the foundation pit. Figure 4 The surface settlement curve is converted into a support displacement input model, and the stress distribution cloud diagram of the masonry building structure is calculated, such as Figure 5 and 6 shown.

[0063] 4) In order to analyze the correlation between the differential settlement of buildings and the excess rate of compressive strength and the excess rate of crack strength, and then obtain the structural performance status, a scatter plot between the excess rate of compressive strength, the excess rate of crack strength and the maximum differential settlement of buildings was drawn based on the analysis of 12 construction conditions, as shown in the figure. Figure 7 As shown in the figure, it can be seen that both the crack resistance excess rate and the compressive resistance excess rate gradually increase with the increase of differential settlement. When the differential settlement is less than 15mm, the structure is in good condition (normal state); when the differential settlement is greater than 15mm and less than 60mm, the structure is in a damaged state (warning state); when the differential settlement is greater than 60mm, the structure is in a damaged state (destructive state).

[0064] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A method for evaluating the performance of a masonry structure adjacent to a foundation pit, characterized in that: The following steps are involved: S1: Establish a three-dimensional finite element model of the foundation pit support and surrounding buildings, and calculate the surrounding ground settlement model δ(x, y) during the foundation pit construction process; S2: Establish a refined finite element model of the masonry structure, input the ground settlement model δ(x, y) into the model, and calculate the stress σ of each wall of the masonry structure i ; S3: Take the single wall j as the unit, according to the stress σ of each wall i The failure distribution of the wall's compressive and tensile strengths, as well as the compressive strength excess rate δ are calculated respectively. c，j and the crack strength excess rate δ t，j ; The step S3 specifically includes: S31: Count the number of units n of wall j j When the unit stress is compressive stress, the number of units n exceeds the material compressive strength σc c，j1 , when the unit stress is tensile stress, it exceeds the tensile strength of the material σ t Number of units n t，j1 ; S32: Calculate the initial value of the compressive strength excess rate δ c，j1 =n c，j1 / n j1 , crack strength excess rateδ t，j1 =n t，j1 / n j1 ; S33: Using the birth-death unit method, the simulated unit stress is compressive stress and tensile stress and exceeds the compressive strength of the material σ c and tensile strength σ t After the wall unit fails, the compressive strength excess rate δ of wall j is calculated again c，j2 , crack strength excess rate δ t，j2 ; S34: Repeat step S33 to calculate the i-th compressive strength exceeding rate δ of wall j c，ji , crack strength excess rate δ t，ji ; S4: According to the compressive strength excess rate δ c，j and the crack strength excess rate δ t，j Determine the performance status of masonry structures; The step S4 specifically includes: S41: When δ t，j ≥20% or δ c，j When ≥5%, the structural performance status is directly judged as damaged; S42: In other cases, according to the compressive strength exceeding rate δ c，ji , crack strength excess rate δ t，ji , and obtain the difference Δδ between two consecutive calculation results c，j(i，i-1) and Δδ t，j(i，i-1) ; S43: Compare the interpolation values ​​of the compressive strength exceeding limit rate Δδ at each time c，j(i，i-1) , the difference of crack strength exceeding limit rate Δδ t，j(i，i-1) , when Δδ c，j(i，i-1) and Δδ t，j(i，i-1) It is judged as destroyed when it increases gradually, and it is judged as safe when it decreases gradually and does not meet the conditions of S41; S44: When other situations occur, it is judged as a warning.

2. The method for evaluating the performance of a masonry structure adjacent to a foundation pit according to claim 1, characterized in that: The step S1 specifically includes: S11: The Mohr-Coulomb model is used to simulate the soil, the plate element is used to simulate the vertical support structure of the foundation pit, and the beam element is used to simulate the foundation pit columns, column piles, supports, cap beams and connecting beams; S12: Contact elements are used to simulate the vertical support structure of the foundation pit and the surrounding soil, the foundation pit column piles and the surrounding soil, and the building pile foundation and the surrounding soil. S13: The birth-death unit method is used to simulate soil excavation, the construction and demolition of the vertical support structure of the foundation pit, the foundation pit columns, column piles, supports, cap beams, and connecting beams, and the surrounding ground settlement model δ(x, y) during the foundation pit excavation process is obtained.

3. The method for evaluating the performance of a masonry structure adjacent to a foundation pit according to claim 2, characterized in that: The vertical supporting structure of the foundation pit includes ground-connected walls and rows of piles.

4. The method for evaluating the performance of a masonry structure adjacent to a foundation pit according to claim 1, characterized in that: The step S2 specifically includes: S21: Shell units are used to simulate masonry walls, and hinged supports are used to simulate foundation settlement. The hinged supports are arranged below the wall units, and the spacing between the supports is not less than 1.0m; S22: According to the plane coordinates (x i ,y i ), and then substitute the surrounding ground settlement model δ(x, y) to obtain the settlement of each hinge support δ(x i ,y i ); S23: The settlement of each hinged support δ(x i ,y i ) is substituted into the refined finite element model of the masonry structure, and the stress σ of each unit of the masonry structure is calculated. i .

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