Method for detecting mechanical state of reinforced concrete composite floor slab after fire
Through high-temperature fire tests and numerical analysis, the structural parameters of composite floor slabs were optimized, solving the problem of shear failure at the joint surface in composite floor slab fires, and realizing the assessment of the mechanical state after fire and the improvement of fire resistance performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG QUANJIAN ENG TESTING CO LTD
- Filing Date
- 2026-01-14
- Publication Date
- 2026-04-28
AI Technical Summary
In a fire, composite floor slabs experience shear stress at the interface between new and old concrete, leading to shear failure at the interface and affecting their stress distribution and fire resistance. Existing technologies make it difficult to effectively assess their mechanical state after a fire.
Through high-temperature fire tests, finite element analysis, and theoretical analysis, structural measures to improve the fire resistance of precast composite slabs are generated, including optimizing parameters such as the ratio of precast slab thickness to post-cast layer thickness and truss reinforcement form. A damage mode feature library is established, and methods for calculating bearing capacity and residual bearing capacity are provided.
Effectively assess the mechanical state of composite floor slabs after a fire, provide structural measures to improve their fire resistance, guide engineering construction, and ensure structural safety.
Smart Images
Figure CN121933387A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of building materials technology, specifically, it relates to a method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire. Background Technology
[0002] Concrete floor slabs are the main components of building structures. Precast assembly of floor slabs can effectively reduce the waste of formwork materials and save labor. They are currently the most mature precast components used in concrete structures. Composite floor slabs with concrete base slabs are an important way to realize the precast assembly of floor slabs.
[0003] Precast concrete composite slabs are a structural form in which a precast concrete base slab is combined with an upper cast-in-place concrete layer to form a whole, working together as a single unit. The bottom reinforcement in the precast slab serves as the bottom load-bearing reinforcement of the composite slab, while the upper cast-in-place concrete layer is equipped with support reinforcement and structural reinforcement. Composite slabs have excellent overall workability and are being widely used in practical engineering projects. Compared with cast-in-place slabs, the bottom reinforcement in precast slabs can be fabricated in the factory, ensuring higher quality. Furthermore, precast slabs can be used as formwork, reducing formwork requirements and shortening the construction period. This is a floor slab type that is currently being strongly promoted and widely applied by the government.
[0004] Composite floor slabs contain a bonding surface between new and old concrete. Under the influence of fire, shear stress caused by temperature gradients will be generated on the bonding surface, which may even lead to shear failure. The stress mode of the composite slab will change. Therefore, the behavior and fire resistance of composite floor slabs in fire are significantly different from those of ordinary floor slabs, and are bound to be more complex. Summary of the Invention
[0005] To address the aforementioned problems and technical deficiencies, this application adopts the following technical solution: a method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, comprising the following steps: High-temperature fire tests were conducted on multiple composite slab components to obtain experimental results; Numerical analysis was performed using the finite element method based on the experimental data to obtain the data analysis results; Theoretical analysis was conducted by combining experimental results and numerical analysis results; Based on theoretical analysis results, structural measures to improve the fire resistance of precast composite slabs are generated to facilitate engineering construction.
[0006] Preferably, the high-temperature fire test uses 12 composite slab components with precast base plates and post-cast concrete layers of different thicknesses. The specimen plane size is 3000mm×3000mm. The thickness of the precast slab and the cast-in-place layer are respectively 40mm+80mm, 40mm+90mm, 60mm+80mm, and 60mm+90mm. Each different thickness uses three different forms of truss reinforcement.
[0007] Preferably, the numerical analysis involves first analyzing the temperature field of the component, and then analyzing its mechanical properties. Temperature field analysis involves calculating the temperature field of a component's cross-section, determining its instantaneous temperature field, obtaining the material's mechanical properties at that temperature, and calculating the temperature stress increment generated by the temperature increment on the cross-section of the composite plate. Mechanical performance analysis is based on the theory of large deflection plates and shells and the thermo-elastic-plastic constitutive theory of materials. A numerical model is established to analyze the fire behavior of composite slabs considering the influence of the bonding surface and joints. The influence of the bonding surface, joint type, floor slab thickness, concrete strength and reinforcement ratio on the fire resistance performance of composite slabs in fire is analyzed.
[0008] Preferably, the theoretical analysis includes: The behavior mechanism of different types of concrete composite slabs in fire is explained from a mechanical perspective; Establish a method for calculating the load-bearing capacity of different types of concrete composite slabs under fire conditions and the remaining load-bearing capacity after the fire.
[0009] Furthermore, the formula for calculating the load-bearing capacity under fire conditions is as follows: N fire =(α1*f c *A C +α2*f y *A s )*β1*β2 Where, N fire The load-bearing capacity under fire conditions, α1 and α2 are thickness combination coefficients, f c f represents the temperature decay strength of concrete. y β1 represents the temperature decay strength of the reinforcing steel, β2 represents the influence coefficient of the overlapping surface, and β3 represents the influence coefficient of the joint.
[0010] Furthermore, the formula for calculating the remaining load-bearing capacity after the fire is as follows: N residual =N fire *γ1*γ2 Where, N residual γ1 represents the remaining load-bearing capacity after the fire, γ2 represents the fire duration coefficient, and γ3 represents the damage repair coefficient.
[0011] Preferably, the generation of the construction measures includes: The core control parameters for the construction parameter set are the thickness ratio of the precast slab to the post-cast layer, the height and inclination angle of the web reinforcement of the truss reinforcement, and the surface roughness grade at the joint. A correspondence diagram of damage modes specific to composite plates is established based on the parameter set; A fire damage mode feature library for composite slabs with unique structures was established based on experimental results and parameter sets. Indirect indicators obtained through non-destructive means, the proportion of concrete spalling area at specific locations on the bottom of the slab, and the width of visible cracks at the joints are quantitatively corrected by mapping the feature library to the corresponding regions in the corresponding relationship diagram.
[0012] Furthermore, the specific damage modes of the composite plate include: The dominant damage types are: peeling at the precast-post-cast interface, high-temperature bursting of concrete above the truss reinforcement, and stress concentration cracking at the joint.
[0013] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the content of the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described above.
[0014] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the content of the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described above.
[0015] Compared to existing technologies, the beneficial effects of this application are as follows: This application obtains experimental results by conducting high-temperature fire tests on multiple composite slab components, proposes a basis for the fire-resistant design of reinforced concrete precast composite slabs, conducts numerical analysis using the finite element method based on the experimental data, obtains data analysis results, and performs theoretical analysis by combining the experimental results and numerical analysis results. Based on the theoretical analysis results, it generates structural measures to improve the fire resistance of precast composite slabs, which are convenient for engineering construction, and provides guidance for the fire-resistant performance-based design of precast concrete composite floor slabs. Attached Figure Description
[0016] In the attached diagram: Figure 1 This is a schematic diagram of the method steps in an embodiment of this application. Detailed Implementation
[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments. Generally, the components of the embodiments of this application described and shown in the accompanying drawings can be arranged and designed in various different configurations.
[0018] Example 1 like Figure 1 As shown, the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire includes the following steps: High-temperature fire tests were conducted on multiple composite slab components to obtain experimental results; The high-temperature fire test used 12 composite slab components with precast base plates and post-cast concrete layers of different thicknesses. The specimens were 3000mm×3000mm in plan size. The thicknesses of the precast slab and the cast-in-place layer were 40mm+80mm, 40mm+90mm, 60mm+80mm, and 60mm+90mm, respectively. For each different thickness, three different forms of truss reinforcement were used.
[0019] Numerical analysis was performed using the finite element method based on the experimental data to obtain the data analysis results; Numerical analysis involves first analyzing the temperature field of the component, and then analyzing its mechanical properties. Temperature field analysis involves calculating the temperature field of a component's cross-section, determining its instantaneous temperature field, obtaining the material's mechanical properties at that temperature, and calculating the temperature stress increment generated by the temperature increment on the cross-section of the composite plate. Mechanical performance analysis is based on the theory of large deflection plates and shells and the thermo-elastic-plastic constitutive theory of materials. A numerical model is established to analyze the fire behavior of composite slabs considering the influence of the bonding surface and joints. The influence of the bonding surface, joint type, floor slab thickness, concrete strength and reinforcement ratio on the fire resistance performance of composite slabs in fire is analyzed.
[0020] Theoretical analysis was conducted by combining experimental results and numerical analysis results; Theoretical analysis includes: The behavior mechanism of different types of concrete composite slabs in fire is explained from a mechanical perspective; Establish a method for calculating the load-bearing capacity of different types of concrete composite slabs under fire conditions and the remaining load-bearing capacity after the fire.
[0021] The formula for calculating the load-bearing capacity under fire conditions is as follows: N fire =(α1*f c *A C +α2*f y *A s )*β1*β2 Where, N fire The load-bearing capacity under fire conditions, α1 and α2 are thickness combination coefficients, f c f represents the temperature decay strength of concrete. y β1 represents the temperature decay strength of the reinforcing steel, β2 represents the influence coefficient of the overlapping surface, and β3 represents the influence coefficient of the joint.
[0022] The formula for calculating the remaining load-bearing capacity after a fire is as follows: N residual =N fire *γ1*γ2 Where, N residual γ1 represents the remaining load-bearing capacity after the fire, γ2 represents the fire duration coefficient, and γ3 represents the damage repair coefficient.
[0023] Based on theoretical analysis results, structural measures to improve the fire resistance of precast composite slabs are generated to facilitate engineering construction.
[0024] The generation of construction measures includes: The core control parameters for the construction parameter set are the thickness ratio of the precast slab to the post-cast layer, the height and inclination angle of the web reinforcement of the truss reinforcement, and the surface roughness grade at the joint. A correspondence diagram of damage modes specific to composite plates is established based on the parameter set; A fire damage mode feature library for composite slabs with unique structures was established based on experimental results and parameter sets. Indirect indicators obtained through non-destructive means, the proportion of concrete spalling area at specific locations on the bottom of the slab, and the width of visible cracks at the joints are quantitatively corrected by mapping the feature library to the corresponding regions in the corresponding relationship diagram.
[0025] Damage modes specific to composite plates include: The dominant damage types are: peeling at the precast-post-cast interface, high-temperature bursting of concrete above the truss reinforcement, and stress concentration cracking at the joint.
[0026] Example 2 Fire tests were conducted on precast ribbed concrete composite slabs under service loads. Fire tests were conducted on 12 composite slab components with different thicknesses of precast base slabs and post-cast concrete layers. The specific details are as follows: The specimens were 3000mm×3000mm in planar dimensions, and the slab thickness (precast slab + cast-in-place layer) was 40mm+80mm, 40mm+90mm, 60mm+80mm, and 60mm+90mm. The specimens were used to distinguish the different forms of the three types of truss reinforcement, and a total of 12 specimens were made.
[0027] Fire tests were conducted on the composite slabs. During the tests, the concrete temperature, steel reinforcement temperature, temperature at the composite surface, and furnace temperature were measured in the thickness direction of the slab. The slab edge corners, in-plane deformation, vertical deformation at 1 / 4 of the distance from the edge, and vertical deformation at mid-span were also tested. The development of cracks on the unexposed side of the composite slab and the failure mode were observed during the tests.
[0028] Fire tests yield accurate numerical results and provide intuitive and clear experimental phenomena. However, the tests are difficult, costly, and have limited measurable data. Therefore, it is necessary to conduct numerical analysis based on the experimental data. Currently, the numerical analysis of concrete slabs at high temperatures mostly adopts the finite element method. This method is carried out in two stages: first, the temperature field of the component is analyzed, and then the mechanical properties are analyzed.
[0029] Temperature field analysis: The mechanical behavior of composite slabs under fire (internal force redistribution, deformation, cracking, etc.) depends on the change of temperature field. Therefore, accurate calculation of the temperature field of the component section is the basis for mechanical analysis of composite slabs. Only after the instantaneous temperature field is determined can the mechanical properties of the material at that temperature be determined, and then the temperature stress increment generated by the temperature increment on the composite slab section be calculated.
[0030] During a fire, the moisture in concrete evaporates continuously, carrying away heat. To make the analysis results more consistent with the actual fire situation, a temperature model considering the moisture content of the floor slab was established based on the existing temperature analysis model, and the accuracy of the model was verified through experimental results.
[0031] Mechanical performance analysis: Based on the large deflection plate and shell theory and the thermo-elastic-plastic constitutive theory of materials, a numerical model for analyzing the fire behavior of composite slabs considering the influence of the bonding surface and joints is established. Numerical analysis is performed using the post-processing function of ABAQUS software. The effectiveness of the numerical analysis model is verified by experimental results. On this basis, the influence of factors such as bonding surface, joint type, floor slab thickness, concrete strength, and reinforcement ratio on the fire resistance performance of composite slabs in fire is analyzed in depth.
[0032] The theoretical research mainly combines experimental and numerical simulation results to explain the behavior mechanism of different types of concrete composite slabs in fire from a mechanical perspective, and then establishes calculation methods and practical calculation formulas for the bearing capacity of different types of concrete composite slabs under fire.
[0033] Studies have shown that conventional cast-in-place floor slabs undergo large deformation during fires, but do not lose their load-bearing capacity or collapse. However, composite slabs, due to the presence of numerous interfaces and joints between new and old concrete, have an adverse effect on their fire resistance. Their mechanical behavior during fires is more complex, and the calculation of their load-bearing capacity differs from that of cast-in-place floor slabs. Therefore, based on the failure criteria of concrete under large deformation and the failure characteristics of composite slabs during fires, a corresponding theory is established to calculate the ultimate load-bearing capacity of composite slabs. The accuracy of the calculation method is then verified through experimental results.
[0034] Through fire resistance tests and numerical simulation analysis of composite slabs, we can understand the temperature field distribution and fire resistance limit of composite slabs.
[0035] Through fire resistance tests and numerical simulation analysis of composite slabs, we aim to understand the stress mechanism of composite slabs throughout the fire process and establish calculation methods for bearing capacity during fire and residual bearing capacity after fire.
[0036] Complete experimental research on concrete composite slabs under the coupled action of high temperature in fire and normal service load, and master the mechanical mechanism, failure mode and fire resistance limit of concrete composite slabs under fire.
[0037] Establish a calculation method for the load-bearing capacity of composite slabs during and after a fire, and propose structural measures to improve the fire resistance of composite slabs.
[0038] Example 3 From a hardware perspective, this application provides an embodiment of an electronic device containing all or part of a method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire. The electronic device includes a service processor and a distributed memory. The service processor is connected to the memory, and the distributed memory stores a service self-management program configured to store machine-readable instructions. The service processor executes the service self-management program, and the instructions, when executed by the processor, implement the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire as described above.
[0039] From a hardware perspective, in order to effectively improve the flexibility, versatility, and efficiency of data acquisition, this application provides an embodiment of an electronic device comprising all or part of a method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire. The electronic device specifically includes the following components: The system includes a processor, memory, a communications interface, and a bus; wherein the processor, memory, and communications interface communicate with each other via the bus; the communications interface is used for information transmission between the core business system, user terminals, and related databases and other related devices for implementing the method of detecting the mechanical state of reinforced concrete composite floor slabs after a fire; the logic controller can be a desktop computer, tablet computer, or mobile terminal, etc., but this embodiment is not limited to these.
[0040] In this embodiment, the logic controller can be implemented with reference to the embodiment of the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, the content of which is incorporated here, and repeated parts will not be described again.
[0041] It is understood that the user terminal may include smartphones, tablet electronic devices, network set-top boxes, portable computers, desktop computers, personal digital assistants (PDAs), in-vehicle devices, smart wearable devices, etc., wherein the smart wearable devices may include smart glasses, smartwatches, smart bracelets, etc.
[0042] In practical applications, the detection method for the mechanical state of reinforced concrete composite floor slabs after a fire can be partially executed on the electronic device side as described above, or all operations can be completed in the client device. The choice can be made based on the processing power of the client device and the limitations of the user's usage scenario, and this application does not impose any limitations on this. If all operations are completed in the client device, the client device may further include a processor.
[0043] The aforementioned client device may have a communication module (i.e., a communication unit) that can communicate with a remote server to achieve data transmission with the server. The server may include a server on the task scheduling center side, and in other implementation scenarios, it may also include a server on an intermediate platform, such as a server on a third-party server platform that has a communication link with the task scheduling center server. The server may include a single computer device, a server cluster composed of multiple servers, or a server structure of a distributed device.
[0044] Example 4 The embodiments of this application also provide a computer-readable storage medium capable of implementing the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, where the execution subject is a server or client as described in the above embodiments. The computer-readable storage medium stores a computer program that, when executed by a processor, implements all the contents of the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, where the execution subject is a server or client as described in the above embodiments.
[0045] The embodiments of this application may be provided as methods, apparatus, or computer program products. Therefore, this application may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, this application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.
[0046] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (devices), and computer program products according to embodiments of this application. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.
[0047] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.
[0048] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.
[0049] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of this application, and these all fall within the protection scope of this application.
Claims
1. A method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, characterized in that, Includes the following steps: High-temperature fire tests were conducted on multiple composite slab components to obtain experimental results; Numerical analysis and testing were conducted using the finite element method based on experimental data. First, the temperature field of the component was analyzed, and then the mechanical properties were analyzed to obtain the data analysis and testing results. Theoretical analysis was conducted by combining experimental results and numerical analysis results to investigate the behavior mechanism of different types of concrete composite slabs in fire from a mechanical perspective. Based on the test results, structural measures were taken to improve the fire resistance of the precast composite slabs.
2. The method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described in claim 1, is characterized in that... The high-temperature fire test used 12 composite slab components with precast base plates and post-cast concrete layers of different thicknesses. The specimens had a planar size of 3000mm×3000mm. The thicknesses of the precast slab and the cast-in-place layer were 40mm+80mm, 40mm+90mm, 60mm+80mm, and 60mm+90mm, respectively. For each different thickness, three different forms of truss reinforcement were used.
3. The method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described in claim 1, is characterized in that... The temperature field analysis involves calculating the temperature field of the component cross section, determining its instantaneous temperature field, obtaining the mechanical properties of the material at that temperature, and calculating the temperature stress increment generated by the temperature increment on the cross section of the composite plate. Based on existing temperature analysis models, a temperature model considering the moisture content of floor slabs was established, and the accuracy of the model was verified through experimental results. Mechanical performance analysis is based on the theory of large deflection plates and shells and the thermo-elastic-plastic constitutive theory of materials, and establishes a numerical analysis model for analyzing the fire behavior of composite plates that takes into account the influence of joints and seams. The effectiveness of the numerical analysis model was verified through experimental results, and the influence of composite surface, joint type, floor slab thickness, concrete strength and reinforcement ratio on the fire resistance performance of composite slabs in fire was analyzed.
4. The method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described in claim 1, is characterized in that... The theoretical analysis includes: Establish a method for calculating the load-bearing capacity of different types of concrete composite slabs under fire conditions and the remaining load-bearing capacity after the fire.
5. The method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described in claim 4, is characterized in that... The formula for calculating the load-bearing capacity under fire conditions is as follows: N fire =(α1*f c *A C +α2*f y *A s )*β1*β2 Where, N fire The load-bearing capacity under fire conditions, α1 and α2 are thickness combination coefficients, f c f represents the temperature decay strength of concrete. y β1 represents the temperature decay strength of the reinforcing steel, β2 represents the influence coefficient of the overlapping surface, and β3 represents the influence coefficient of the joint.
6. The method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described in claim 5, is characterized in that... The formula for calculating the remaining load-bearing capacity after the fire is as follows: N residual =N fire *c1*c2 Where, N residual γ1 represents the remaining load-bearing capacity after the fire, γ2 represents the fire duration coefficient, and γ3 represents the damage repair coefficient.
7. The method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described in claim 1, is characterized in that... The generation of the construction measures includes: The core control parameters for the construction parameter set are the thickness ratio of the precast slab to the post-cast layer, the height and inclination angle of the web reinforcement of the truss reinforcement, and the surface roughness grade at the joint. A correspondence diagram of damage modes specific to composite plates is established based on the parameter set; A fire damage mode feature library for composite slabs with unique structures was established based on experimental results and parameter sets. Indirect indicators obtained through non-destructive means, the proportion of concrete spalling area at specific locations on the bottom of the slab, and the width of visible cracks at the joints are quantitatively corrected by mapping the feature library to the corresponding regions in the corresponding relationship diagram.
8. The method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described in claim 7, is characterized in that... The specific damage modes of the composite plate include: The dominant damage types are: peeling at the precast-post-cast interface, high-temperature bursting of concrete above the truss reinforcement, and stress concentration cracking at the joint.
9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the content of the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire as described in claim 1.
10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the method for detecting the mechanical state of reinforced concrete composite floor slabs after a fire, as described in claim 1.