Performance-based evaluation method for vertical bearing capacity of existing masonry structure wall
By considering factors such as backfill soil in the building core, floor slab constraints, and long-term compaction effects, and by adjusting the bearing capacity calculation using reliability theory, the inaccuracy of existing building safety assessments in current technologies has been resolved, resulting in a more scientific and objective safety assessment and reducing unnecessary reinforcement and demolition.
Patent Information
- Application Number
- CN202511083674.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-04
- Publication Date
- 2025-12-16
AI Technical Summary
Existing technologies cannot accurately assess the safety of existing buildings, leading to a large number of buildings being misjudged as unsafe, resulting in unnecessary reinforcement and demolition. Furthermore, the rating methods are subjective and unreasonable.
By considering factors such as backfill soil in the building core, floor slab constraints, long-term compaction effect and dead load variability, an evaluation method based on reliability theory is adopted, the bearing capacity calculation formula is adjusted, including the introduction of coefficients m, n and k, and the safety assessment grading standard is reclassified.
This improved the scientific rigor and objectivity of the assessment, reduced the proportion of C and D grade assessment results, avoided unnecessary structural reinforcement and demolition, and provided a more accurate basis for safety assessment.
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Figure CN121145503A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of building safety appraisal, and particularly relates to a performance-based evaluation method for vertical bearing capacity of existing masonry structure walls. BACKGROUND
[0002] The area of existing masonry structures in China is about 60 billion square meters, and a large number of masonry structures are approaching or exceeding the service life. According to relevant laws and regulations of the state, existing buildings exceeding the service life or before modification shall be appraised, including seismic appraisal and safety appraisal. The seismic appraisal is based on the national standard "Building Seismic Appraisal Standard" GB50023, which adopts different standards for buildings of different construction years, namely, "old people old method, new people new method". The safety appraisal is based on the national standard "Civil Building Reliability Appraisal Standard" GB50292, and the appraisal method of "Civil Building Reliability Appraisal Standard" GB50292 applies the requirements of the current design specification, and the grade difference of safety appraisal classification is very small. As is known to all, the design specification of China is basically revised every ten years, which leads to the fact that the safety level of existing buildings cannot keep up with the pace of newly built design specifications. If the existing buildings are not appraised, most of them will be classified as C and D levels after safety appraisal, causing panic of managers and users, and general questioning of practitioners: is the conclusion from this appraisal method "really dangerous", or is it "calculated danger" caused by the continuous improvement of standards? It is necessary to re-examine the rationality and objectivity of the safety appraisal method of existing buildings.
[0003] The existing rating method has the following problems: 1) The load specification gradually increases the value, which leads to the fact that the buildings that originally meet the specification and are still within the normal and reasonable service life become unsafe buildings after appraisal. For example, according to the 2015 specification adjustment, the load sub-item coefficient is increased from 1.2 and 1.4 to 1.3 and 1.5, respectively. For this item alone, the calculation results differ by 7%-8%. The original design safety factor of 1.0 is reduced to 0.93-0.92, which changes from A level to C level. 2) In the component rating, the number is simply counted without considering the importance and influence of the components. For example, the vertical components (walls and columns) are more important than beams and slabs, beams are more important than slabs, and the vertical components of the bottom layer are more important than those of the top layer. 3) For masonry structures, the "Masonry Structure Design Specification" requires that the calculation height of the bottom wall is 500mm from the outdoor ground. The indoor and outdoor height difference is 450-600mm, and the calculation height becomes 3.8-4m after returning 500mm. The strength reduction coefficient of the wall caused by the high-thickness ratio φThe value can reach about 0.5, the reduction is very large, the calculation result is very low, and almost 80-90% of the existing masonry structure safety appraisal is rated as C and D, which is a kind of calculated 'unsafe'. 4) Regarding the constant load sub-item coefficient, the existing appraisal method is still taken as 1.3 according to the requirement of the existing design specification, the design specification considers the variability problem of the section masonry or pouring in the construction process, and for the existing building, the section size and density are determined and will not vary again, and the result determined according to the measured size is not suitable for further amplifying the variability influence of the constant load. There is no relatively accurate safety appraisal method for the existing building, which leads to unnecessary structure reinforcement and waste of manpower and material resources. SUMMARY
[0004] The purpose of the present application is to provide a performance-based evaluation method and measurement method for the vertical bearing capacity of the existing masonry structure wall, which can solve the problem that the safety of the existing building cannot be accurately identified in the prior art.
[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A performance-based evaluation method for the vertical bearing capacity of the existing masonry structure wall, comprising the following steps: Step 1, determining the calculation height of the bottom wall and calculating the vertical bearing capacity considering the constraint effect of the indoor backfill soil and the rigid floor of the existing masonry structure; Step 2, determining the calculation height of each layer of wall and calculating the vertical bearing capacity considering the constraint effect of each layer of floor of the existing masonry structure; Step 3, calculating the vertical bearing capacity of the wall considering the long-term compression effect of the existing masonry structure wall; Step 4, considering the constant load variability of the existing masonry structure wall; Step 5, grading the safety appraisal of the masonry structure wall based on the reliability theory.
[0006] Preferably, in step 1, the vertical bearing capacity of the wall model before and after adding the backfill soil and tamping the existing masonry structure is compared through the vertical bearing capacity comparison test and finite element simulation, and the vertical bearing capacity calculation formula of the bottom wall considering the constraint effect of the indoor backfill soil and the rigid floor of the existing masonry structure is obtained as follows: N ≤ mφfA In the formula, N is the design value of the vertical force of the calculation wall; m is the bearing capacity improvement coefficient of the wall considering the constraint effect of the house core backfill soil and the rigid floor; φ is the influence coefficient of the high-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, which is obtained from the table in the 'Code for Design of Masonry Structures'; f is the compressive strength design value of the existing masonry structure; A is the cross-sectional area of the wall.
[0007] Preferably, the value of m is calculated by interpolation according to the compaction coefficient of the backfill soil, when the compaction coefficient of the backfill soil is 0.9, m is 1.0, and when the compaction coefficient is 0.95 or above, m is 1.2.
[0008] Preferably, in the second step, the vertical bearing capacity formula of each layer of the wall considering the constraint effect of the existing masonry structure floor is obtained through vertical bearing capacity comparison test and finite element simulation of the wall model of the top floor: N ≤ nφf A In the formula, N is the design value of the vertical force of the wall; n is the bearing capacity improvement coefficient of the wall considering the constraint of the top floor; φ is the influence coefficient of the height-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, which is obtained from the table in the Code for Design of Masonry Structures; f is the design value of the compressive strength of the existing masonry structure; A is the cross-sectional area of the wall.
[0009] Preferably, when the cast-in-place floor roof is used, n is 1.1; when the prefabricated floor roof is used, n is 1.05; and when the wooden floor roof is used, n is 1.0.
[0010] Preferably, in the third step, the vertical bearing capacity formula of the wall considering the long-term compression state of the existing masonry structure wall is obtained through vertical bearing capacity comparison test and finite element simulation of the wall model simulating the construction process and the static state: N ≤ kφf A In the formula, N is the design value of the vertical force of the wall; k is the bearing capacity improvement coefficient of the wall considering the long-term compression effect; φ is the influence coefficient of the height-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, which is obtained from the table in the Code for Design of Masonry Structures; f is the design value of the compressive strength of the existing masonry structure; A is the cross-sectional area of the wall.
[0011] Preferably, for a six-story existing masonry structure, the bottom layer k is 1.15, the top layer k is 1.0, and the rest of the layers are calculated by interpolation.
[0012] Preferably, the constant load variability value of the existing masonry structure wall is adjusted by the constant load partial coefficient, and the value range of the constant load partial coefficient is 1-1.1.
[0013] Preferably, based on the reliability theory, the safety appraisal grading standards of the existing masonry structure are re-divided, and the proportion of C and D level appraisal results is reduced through actual case calculation.
[0014] In the present application, by considering the beneficial effects of the constraint effect of the house core backfill soil and the floor, the long-term compaction effect of the wall body, etc., a grading method based on reliability is established, which can more truly reflect the actual bearing capacity of the wall body compared with the traditional method, so that a large number of buildings rated as C and D levels are changed to B level, avoiding unnecessary vertical bearing capacity reinforcement or demolition of a large number of existing masonry structures, turnover relocation and demolition of a large amount of construction waste, and the comprehensive economic and social benefits are remarkable.
[0015] Considering the variability of the dead load of the existing masonry structure wall, the dead load partial coefficient is adjusted, the dead load partial coefficient of the existing standard for new buildings is higher, while the existing masonry structure has been used for many years, the variability of the measured cross-sectional size, material performance, density and other indicators is very small, and the brick wall cracking load has a large margin. The present application adjusts the characteristics of the existing structure, so that the evaluation method is more suitable for the actual situation of the existing masonry structure, and the scientificity of the evaluation is improved.
[0016] The safety appraisal grading standards of the existing masonry structure are re-divided, which avoids the subjective bias that may occur in the previous appraisal. For example, the existing component safety appraisal grading standards have certain limitations, and the present application reduces the proportion of C and D level appraisal results through actual case calculation, so that the safety appraisal results of the masonry wall are more objective and reasonable. This helps the building industry to have a more accurate understanding of the safety of the existing masonry structure, and provides a reliable basis for subsequent maintenance, reconstruction and other decisions. BRIEF DESCRIPTION OF DRAWINGS
[0017] Figure 1 A comparison test diagram for considering the calculation height of the wall body constrained by the house core backfill soil and the floor; Figure 2 A finite element analysis diagram of the test model; Figure 3 A wall bearing capacity test process diagram considering the long-term compaction effect of the existing masonry wall; DETAILED DESCRIPTION
[0018] The present application will be further described below in conjunction with the drawings: A performance-based vertical bearing capacity evaluation method for existing masonry structure wall, comprising the following steps: Step one, the determination of the calculation height of the bottom wall considering the constraint effect of the existing masonry structure indoor backfill soil and rigid floor. Through the vertical bearing capacity comparison test and finite element simulation of the wall model before and after adding backfill soil and tamping the existing masonry structure, the vertical bearing capacity formula of the bottom wall considering the constraint effect of the existing masonry structure indoor backfill soil and rigid floor is obtained as follows: N ≤ mφfA In the formula, N is the design value of the vertical force of the calculation wall; m is the bearing capacity improvement coefficient of the wall considering the constraint effect of the house core backfill soil and rigid floor; φ is the influence coefficient of the high-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, which is obtained from the table in the Code for Design of Masonry Structures; f is the design value of the compressive strength of the existing masonry structure; A is the cross-sectional area of the calculation wall.
[0019] In the above formula, N is the design value of the vertical force of the calculation wall, and f*A is the vertical bearing capacity of the calculation wall. However, the greater the wall height, the greater the high-thickness ratio of the wall with a certain thickness, and the poorer the stability. Similarly, the eccentricity also has this problem. Therefore, the influence of the high-thickness ratio and the eccentricity on the vertical bearing capacity of the wall is reflected, that is, the influence coefficient φ is used to express it.
[0020] Specifically, the value of m is calculated by interpolation according to the size of the backfill soil tamping coefficient. When the backfill soil tamping coefficient is 0.9, m is 1.0, and when the tamping coefficient is 0.95 and above, m is 1.2. For each calculation wall, the design value of the compressive strength f of the existing masonry structure and the cross-sectional area A of the calculation wall are fixed values. When the value of φ is selected, the maximum height of the calculation wall can be calculated.
[0021] Step two, the determination of the calculation height of each layer of wall considering the constraint effect of each layer of floor of the existing masonry structure; through the vertical bearing capacity comparison test and finite element simulation of the wall model of the top floor, the vertical bearing capacity formula of each layer of wall considering the constraint effect of the floor of the existing masonry structure is obtained as follows: N ≤ nφf A In the formula, N is the design value of the vertical force of the calculation wall; n is the bearing capacity improvement coefficient of the wall considering the constraint of the top floor; φ is the influence coefficient of the high-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, which is obtained from the table in the Code for Design of Masonry Structures; f is the design value of the compressive strength of the existing masonry structure; A is the cross-sectional area of the calculation wall.
[0022] In the above formula, N is the design value of the axial force of the wall, and f*A is the calculated vertical bearing capacity of the wall. However, the greater the wall height and the greater the height-to-thickness ratio of a wall of a certain thickness, the worse its stability. Similarly, eccentricity is also a problem. Therefore, the influence of the wall stability on the vertical bearing capacity of the wall is reflected by the height-to-thickness ratio and eccentricity, which is expressed by the influence coefficient φ.
[0023] Specifically, when the floor or roof is cast-in-place, n is 1.1; when the floor or roof is precast, n is 1.05; and when the floor or roof is wooden, n is 1.0. The design value of the compressive strength f of the existing masonry structure for each calculated wall, and the cross-sectional area A of the calculated wall, are also fixed values. Once the value of φ is selected, the maximum vertical bearing capacity of the calculated wall can be calculated.
[0024] Step 3: Perform wall bearing capacity calculation considering the long-term compaction effect of existing masonry wall structures; Through comparative tests and finite element simulations of the vertical bearing capacity of wall models under simulated construction and static conditions, the formula for calculating the vertical bearing capacity of existing masonry walls under long-term compaction conditions is derived as follows: N ≤ kφf A In the formula, N is the design value for the vertical force of the wall. k is the wall bearing capacity enhancement coefficient considering the long-term compaction effect of the wall; φ is the influence coefficient of the height-to-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, and the value is obtained from the table in the "Code for Design of Masonry Structures"; f is the design value of the compressive strength of the existing masonry structure; A represents the calculated cross-sectional area of the wall.
[0025] In the above formula, N is the design value of the axial force of the wall, and f*A is the calculated vertical bearing capacity of the wall. However, the greater the wall height and the greater the height-to-thickness ratio of a wall of a certain thickness, the worse its strength. Similarly, eccentricity also has this problem. Therefore, the influence of wall stability on the vertical bearing capacity of the wall is reflected by the height-to-thickness ratio and eccentricity, which is expressed by the influence coefficient φ.
[0026] Specifically, for a six-story existing masonry structure, k is taken as 1.15 for the bottom floor and 1.0 for the top floor, with the remaining floors calculated using interpolation. The design value of the compressive strength f of the existing masonry structure for each calculated wall and the cross-sectional area A of the calculated wall are also fixed values. Once the φ value is selected, the maximum height of the calculated wall can be calculated, thus obtaining the wall strength at the maximum height.
[0027] Step 4: Consider the variability of the dead load on existing masonry wall structures. This variability is adjusted using a partial factor for the dead load, with a range of 1 to 1.1. The current "Code for Design of Masonry Structures" GB50003 uses a partial factor of 1.2 for the dead load, which was further increased to 1.3 after the implementation of the general code. This was to account for potential variability during actual construction. However, for existing masonry structures, the measured variability in cross-sectional dimensions, material properties, density, and other indicators is very small. Furthermore, extensive vertical load compressive strength tests show that the cracking load of brick walls is approximately 50% to 70% of the ultimate load, providing a significant margin. Therefore, for existing masonry structures that have been in normal use for many years without vertical cracks, a range of 1 to 1.1 for the dead load partial factor is reasonable.
[0028] Step 5: Classify the safety assessment of masonry wall structures based on reliability theory. Based on reliability theory, the existing safety assessment classification standards for masonry structures are redefined. Through calculations using real-world cases, the proportion of C and D grade assessment results is reduced. This makes the safety assessment results for masonry walls more objective and reasonable, avoiding unnecessary demolition or excessive reinforcement of many buildings that have been in normal use for many years.
[0029] The current structural component safety assessment ratings are as follows: 1) Components with a safety factor greater than 1.0 are classified as Grade A; 2) Components with a safety factor between 0.95 and 1.0 are classified as Grade B; 3) Components with a safety factor between 0.9 and 0.95 are classified as Grade C; 4) Components with a safety factor less than 0.9 are classified as Grade D. Then, for each floor, the number of components of different grades is counted, and the lowest grade component is used as the rating for that floor (A / B / C / D). Finally, the rating result of the lowest grade among all floors and the foundation is used as the rating result for the entire structure.
[0030] By introducing the coefficients m, n, and k (through experiments and theoretical analysis), the calculation results of the vertical bearing capacity of the wall are improved. Combined with the experimental result that the cracking load of the wall is about 50-70% of the ultimate load of the wall, about 50% of the C and D grade appraisal results of walls that have not developed vertical bearing cracks during normal use can be revised.
[0031] The formulas in the dependent claims are all verification formulas for the vertical bearing capacity of the wall. The "calculated height" mentioned in claim 1 is reduced by taking into account the lateral restraint effect of the backfill soil in the building core, the rigid floor, and the floor slabs on each floor on the wall, thereby reducing the calculated height-to-thickness ratio of the wall, further correcting the fai value that takes into account the influence of the height-to-thickness ratio, and finally reflecting it in the vertical bearing capacity calculation formula.
[0032] The above embodiments are merely illustrative of the concept and implementation of the present invention and are not intended to limit it. Under the concept of the present invention, technical solutions without substantial changes are still within the scope of protection.
Claims
1. A performance-based method for evaluating the vertical bearing capacity of existing masonry structural walls, characterized in that, Includes the following steps: Step 1: Determine the calculated height of the bottom wall and calculate the vertical bearing capacity, taking into account the constraints of the existing masonry structure's indoor backfill soil and rigid floor. Step 2: Determine the calculated height of the walls on each floor, taking into account the constraint effect of the existing masonry structure floor slabs, and calculate the vertical bearing capacity. Step 3: Calculate the vertical bearing capacity of the wall considering the long-term compaction effect of the existing masonry structure wall; Step 4: Consider the variability of the dead load on the existing masonry structure walls; Step 5: Classify the safety assessment of masonry wall structures based on reliability theory.
2. The performance-based method for evaluating the vertical bearing capacity of existing masonry structural walls according to claim 1, characterized in that: In step one, through comparative tests and finite element simulations of the vertical bearing capacity of the wall models before and after adding backfill soil and compacting the existing masonry structure, the calculation formula for the vertical bearing capacity of the bottom wall considering the indoor backfill soil and rigid floor constraint of the existing masonry structure is obtained as follows: N ≤ mφfA In the formula, N To calculate the design value of the vertical force on the wall; m The coefficient for increasing the vertical bearing capacity of the wall is taken into account for the restraining effect of the backfill soil in the building core and the rigid floor. φ is the influence coefficient of the height-to-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, and the value is obtained from the table in the "Code for Design of Masonry Structures"; f This is the design value for the compressive strength of the existing masonry structure; A To calculate the cross-sectional area of the wall.
3. The performance-based method for evaluating the vertical bearing capacity of existing masonry structural walls according to claim 2, characterized in that: The m The value is calculated by interpolation based on the compaction coefficient of the backfill soil. When the compaction coefficient of the backfill soil is 0.9, m Take 1.0; when the compaction coefficient is 0.95 or higher, m Take 1.
2.
4. The performance-based method for evaluating the vertical bearing capacity of existing masonry wall structures according to claim 1, characterized in that: In step two, through comparative tests and finite element simulations of the vertical bearing capacity of the wall model of the top floor slab, the formulas for the vertical bearing capacity of each layer of walls considering the constraint effect of the existing masonry structure floor slab are derived as follows: N ≤ nφf A In the formula, N is the design value for the vertical force of the wall. n is the wall bearing capacity enhancement factor considering the constraint of the top floor slab; φ is the influence coefficient of the height-to-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, and the value is obtained from the table in the "Code for Design of Masonry Structures"; f This is the design value for the compressive strength of the existing masonry structure; A To calculate the cross-sectional area of the wall.
5. The performance-based method for evaluating the vertical bearing capacity of existing masonry structural walls according to claim 4, characterized in that: When building a cast-in-place floor slab roof n Take 1.1; when it is a precast roof, n Take 1.05; when it is a wooden roof, n Take 1.
0.
6. The measurement method for evaluating the vertical bearing capacity of existing masonry structural walls based on performance, as described in claim 1, is characterized in that: In step three, through comparative tests of the vertical bearing capacity of wall models under simulated construction and static conditions, and finite element simulation, the formula for calculating the vertical bearing capacity of existing masonry wall structures under long-term compaction conditions is derived as follows: N ≤ kφf A In the formula, N is the design value for the vertical force of the wall. k is the wall bearing capacity enhancement coefficient considering the long-term compaction effect of the wall; φ is the influence coefficient of the height-to-thickness ratio β and the eccentricity e of the axial force on the bearing capacity of the compression member, and the value is obtained from the table in the "Code for Design of Masonry Structures"; f This is the design value for the compressive strength of the existing masonry structure; A To calculate the cross-sectional area of the wall.
7. The measurement method for evaluating the vertical bearing capacity of existing masonry structural walls based on performance, as described in claim 6, is characterized in that: For a six-story existing masonry structure, k is taken as 1.15 for the bottom floor and 1.0 for the top floor, and the remaining floors are calculated by interpolation.
8. The measurement method for evaluating the vertical bearing capacity of existing masonry structural walls based on performance, as described in claim 1, is characterized in that: In step four, the variability of the dead load of the existing masonry structure wall is adjusted by the dead load partial factor, which ranges from 1 to 1.
1.
9. The measurement method for evaluating the vertical bearing capacity of existing masonry structural walls based on performance, as described in claim 1, is characterized in that: Based on reliability theory, the existing safety assessment and grading standards for masonry structures are reclassified to reduce the proportion of C and D grade assessment results.