A method for predicting nonlinear response of a double-steel-plate fiber-reinforced concrete composite beam

Abstract

The application relates to a nonlinear response prediction method of a double-steel-plate fiber-reinforced concrete composite beam, which comprises the following steps: obtaining material parameters and geometric parameters of the double-steel-plate fiber-reinforced concrete, deducing the stiffness, load and deflection of each stage in the loading process based on the plane stress-strain distribution, and restraining the prediction range by means of the upper and lower limits of the deflection in the nonlinear working stage, so as to realize the prediction of the whole loading process of the double-steel-plate fiber-reinforced concrete. The application can accurately predict the nonlinear response of the composite beam.

Description

Technical Field

[0001] This invention belongs to the field of material performance prediction technology, specifically relating to a method for predicting the nonlinear response of a double steel plate-fiber reinforced concrete composite beam. Background Technology

[0002] Double-plate fiber-reinforced concrete composite beams are a novel type of composite structure widely used in bridges, high-rise buildings, and industrial infrastructure. These beams are constructed by sandwiching a layer of fiber-reinforced concrete between two steel plates, thus combining the properties of both steel and concrete. Specifically, double-plate fiber-reinforced concrete composite beams exhibit excellent strength and toughness, while also possessing good compressive properties and crack control capabilities.

[0003] While double-plate fiber-reinforced concrete composite beams possess excellent mechanical properties, their nonlinear response becomes difficult to obtain when the beam's geometry is asymmetrical (i.e., the upper and lower plates have different thicknesses). Consequently, the structural safety and reliability cannot be accurately quantified. For instance, existing models can only predict the behavior of the composite structure during the elastic phase and before the yield point, failing to comprehensively predict the entire response process from the initial loading stage to failure. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for predicting the nonlinear response of double steel plate-fiber reinforced concrete composite beams, which solves the problem that existing technologies cannot comprehensively predict the nonlinear response of asymmetric double steel plate-fiber reinforced concrete composite beams.

[0005] The technical solution of the present invention is as follows: A method for predicting the nonlinear response of a double-steel-plate fiber-reinforced concrete composite beam includes the following steps: S1) Obtain the material parameters of the double steel plate-fiber reinforced concrete composite beam; The material parameters include: Elastic modulus of steel plate steel plate yield strength Ultimate strength of steel plate Yield strain of tensile steel plate Elastic modulus of fiber-reinforced concrete The compressive strength of fiber-reinforced concrete Tensile strength of fiber-reinforced concrete The ultimate strain of fiber-reinforced concrete in the tensile elastic segment. Ultimate strain of the tensile plateau segment of fiber-reinforced concrete. The ultimate tensile strain of fiber-reinforced concrete Beam span, Upper steel plate thickness, Lower steel plate thickness, core material height, Core material width; S2) Calculate the stiffness of the double-plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. and cracking load And based on stiffness and cracking load Calculate the deflection in the elastic stage of the entire cross section ; S3) Calculate the stiffness of the double-plate-fiber-reinforced concrete composite beam in the elastic working stage with cracks. and yield load And based on stiffness Yield load Cracking load and deflection Calculate the deflection during the elastic working stage of the cracked structure. ; S4) Calculate the upper limit of stiffness of the double steel plate-fiber reinforced concrete composite beam in the nonlinear operating stage. Stiffness lower limit and ultimate load And based on the upper limit of stiffness Ultimate load Yield load and deflection Calculate the upper limit of deflection during the nonlinear working phase. Based on the lower limit of stiffness Ultimate load Yield load and deflection Calculate the lower limit of deflection during the nonlinear operating phase. ; S5) Based on the stiffness, load and deflection calculation results of steps S2) to S4), plot the load-deflection curves of the double steel plate-fiber reinforced concrete composite beam to predict the nonlinear response of the double steel plate-fiber reinforced concrete composite beam.

[0006] Further, in step S2), the stiffness of the double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section is calculated. and cracking load And based on stiffness and cracking load Calculate the deflection in the elastic stage of the entire cross section Medium stiffness The calculation formula is as follows: ; ; ; In the formula, The stiffness of the double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. EI 1 represents the flexural stiffness of the section in the elastic stage of the entire cross-section. For the beam span, S 1 represents the shear stiffness of the section in the elastic stage of the entire cross section. The elastic modulus of the steel plate. For the core material width, For the thickness of the upper steel plate, For the thickness of the lower steel plate, d The total thickness of the cross section. To improve the elastic modulus of fiber-reinforced concrete, For core material height; Cracking load The calculation formula is as follows: ; In the formula, The cracking load of a double steel plate-fiber reinforced concrete composite beam in the full-section elastic stage. To enhance the tensile strength of fiber-reinforced concrete; Deflection The calculation formula is as follows: ; In the formula, This represents the deflection of the double steel plate-fiber reinforced concrete composite beam at the end of the full-section elastic stage.

[0007] Further, in step S3), the stiffness of the double steel plate-fiber reinforced concrete composite beam during the elastic working stage with cracks is calculated. and yield load And based on stiffness Yield load Cracking load and deflection Calculate the deflection during the elastic working stage of the cracked structure. Medium stiffness The calculation formula is as follows: ; ; ; In the formula, The stiffness of the double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. EI 2 represents the flexural stiffness during the elastic working stage with cracks. S 2 represents the shear stiffness during the elastic working stage with cracks; Yield load The calculation formula is as follows: ; In the formula, x The height of the compression zone of the cross section. This refers to the ultimate strain of the tensile elastic segment of fiber-reinforced concrete. The ultimate strain of the tensile plateau segment of fiber-reinforced concrete. The tensile ultimate strain of fiber-reinforced concrete, Tensile strength of fiber-reinforced concrete; Deflection The calculation formula is as follows: ; In the formula, This represents the deflection at the end of the elastic working phase with cracks.

[0008] Further, in step S4), the upper limit of stiffness of the double steel plate-fiber reinforced concrete composite beam is calculated during the nonlinear working stage. Stiffness lower limit and ultimate load And based on the upper limit of stiffness Ultimate load Yield load and deflection Calculate the upper limit of deflection during the nonlinear working phase. Based on the lower limit of stiffness Ultimate load Yield load and deflection Calculate the lower limit of deflection during the nonlinear operating phase. In the middle, the upper limit of stiffness The calculation formula is as follows: ; ; ; In the formula, This represents the upper limit of stiffness for a double-plate fiber-reinforced concrete composite beam during the nonlinear operating phase. S 3 represents the shear stiffness during the nonlinear working stage. EI 3-up This represents the upper limit of bending stiffness during the nonlinear operating phase. is the stiffness degradation coefficient of the steel plate; Stiffness lower limit The calculation formula is as follows: ; ; In the formula, EI 3-down This represents the lower limit of bending stiffness during the nonlinear operating stage. ultimate load The calculation formula is as follows: ; ; ; In the formula x 压 The height of the concrete compression zone. x 拉 This refers to the height of the tension zone of the concrete. Upper limit of deflection The calculation formula is as follows: ; In the formula, the upper limit of deflection at the end of the nonlinear working phase is... Lower limit of deflection The calculation formula is as follows: ; In the formula, This represents the lower limit of deflection at the end of the nonlinear working phase.

[0009] Further, step S5) involves plotting the load-deflection curves of the double-plate-fiber-reinforced concrete composite beam based on the stiffness, load, and deflection calculation results from steps S2) to S4) to predict the nonlinear response of the double-plate-fiber-reinforced concrete composite beam. The nonlinear response of the double-plate-fiber-reinforced concrete composite beam is characterized using the deflection-load curve. This step also includes the following steps: S51) with stiffness As the slope of the first stage of the deflection-load curve, the cracking load... The load value corresponding to the end of the first stage is expressed in terms of deflection. The deflection value corresponding to the end point of the first stage; S52) with stiffness As the slope of the second stage of the deflection-load curve, the yield load... The load value corresponding to the end of the second stage is expressed in terms of deflection. The deflection value corresponding to the end point of the second stage; S53) with upper limit of stiffness and lower limit of stiffness These are respectively used as the slopes of the third stage of the deflection-load curve, with the ultimate load as the reference. The load value corresponding to the end of the third stage is the upper limit of deflection. As the upper limit of stiffness Corresponding ultimate load The deflection value; with the lower limit of deflection As the lower limit of stiffness Corresponding ultimate load The deflection value.

[0010] Furthermore, in step S53), the upper limit of stiffness is used. The deflection-load curve for the third stage is plotted when the ultimate load is reached. After that, the load value no longer changes while the deflection value continues to increase until it reaches the lower limit of stiffness. The curves drawn intersect.

[0011] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: 1. The technical solution provided in this application can be used to predict the nonlinear response of double steel plate-fiber reinforced concrete throughout the entire process, breaking through the limitations of traditional prediction methods that can only predict the full-section elastic and cracked elastic stages. It has a wider range of applications and significantly enhanced practicality.

[0012] 2. The prediction method provided in this application takes into account the contribution of the tensile strength of fiber-reinforced concrete to the structural stiffness and bearing capacity, refines the prediction model, reduces prediction error, and improves the accuracy of predicting the nonlinear response of composite beams.

[0013] 3. In the third stage, the prediction range of the nonlinear response of the composite beam was further narrowed by using upper and lower limits of stiffness, which solved the problem of difficulty in predicting due to stiffness degradation in this stage and improved the completeness of the prediction. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 The load-deflection curves of the double steel plate-fiber reinforced concrete composite beam during the loading process; Figure 2 This is a stress-strain distribution diagram of a double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. Figure 3 Stress-strain distribution diagram of double steel plate-fiber reinforced concrete composite beam during the elastic working stage with cracks; Figure 4 The stress-strain distribution diagram of the double steel plate-fiber reinforced concrete composite beam during the nonlinear working stage; Figure 5 The graph shows a comparison between the predicted results and the actual experimental results for each embodiment. Detailed Implementation

[0015] To more clearly illustrate the overall concept of this application, a detailed description is provided below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application; however, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below. As described in the background art, when the upper and lower steel plates of a double steel plate-fiber reinforced concrete composite beam have different thicknesses, the composite beam exhibits an unpredictable nonlinear response during loading, and the existing technology has failed to provide a reasonable or accurate prediction method.

[0016] As attached Figure 1 As shown, the response process of the double steel plate-fiber reinforced concrete composite beam under three-point bending loading can be divided into four stages.

[0017] The first stage is the full-section elastic stage. In this stage, both the upper and lower steel plates and the fiber-reinforced concrete are in a state of elastic deformation. As the load continues to increase, the tensile fiber-reinforced concrete reaches its elastic limit strain. At this point, the stiffness of the composite beam is provided jointly by the upper and lower steel plates and the full-section fiber-reinforced concrete. The external load corresponding to the tensile fiber-reinforced concrete reaching its limit strain is the cracking load.

[0018] The second stage is the elastic working stage with cracks. In this stage, cracks appear in the tension zone of the fiber-reinforced concrete, but the composite beam still exhibits elastic behavior, and its stiffness decreases compared to the full-section elastic stage. As the load continues to increase, the tension steel plate reaches its yield strain, at which point the external load on the composite beam is the yield load.

[0019] The third stage is the nonlinear working stage, which is the most challenging part of the prediction. In the nonlinear working stage, the stiffness of the composite beam gradually decreases as the load continues to increase. As the mid-span deflection continues to increase, the tension steel plate reaches its ultimate strength and is close to failure. At this point, the external load corresponding to the composite beam is the ultimate load.

[0020] The fourth stage is the plateau stage. At this stage, the structure's stiffness significantly degrades, mid-span deflection increases while load-bearing capacity no longer improves. This stage is determined by the third stage and requires no further prediction.

[0021] As attached Figure 2 As shown, the stiffness is derived from the stress-strain distribution diagram at the interface of the composite beam in the full-section elastic stage. and cracking load For a double-steel-plate fiber-reinforced concrete composite beam under three-point bending loading, the mid-span deflection consists of the deflection caused by bending deformation and the deflection caused by shear deformation. According to the beam's deflection curve equation, the following can be obtained: ; ; ; In the formula, The stiffness of the double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. EI 1 represents the bending stiffness in the elastic stage of the entire cross section. For the beam span, S 1 represents the shear stiffness in the elastic stage of the entire cross section. The elastic modulus of the steel plate. For the core material width, For the thickness of the upper steel plate, For the thickness of the lower steel plate, d The total thickness of the cross section. To improve the elastic modulus of fiber-reinforced concrete, For core material height; Cracking load The calculation formula is as follows: ; In the formula, The cracking load of a double steel plate-fiber reinforced concrete composite beam in the full-section elastic stage. To enhance the tensile strength of fiber-reinforced concrete; Deflection The calculation formula is as follows: ; In the formula, This represents the deflection of the double steel plate-fiber reinforced concrete composite beam at the end of the full-section elastic stage.

[0022] As attached Figure 3 As shown, the stiffness is derived based on the stress-strain distribution diagram during the elastic working stage with cracks. and yield load .

[0023] stiffness The calculation formula is as follows: ; ; ; In the formula, The stiffness of the double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. EI 2 represents the flexural stiffness during the elastic working stage with cracks. S 2 represents the shear stiffness during the elastic working stage with cracks; Yield load The calculation formula is as follows: ; In the formula, x The height of the compression zone of the cross section. This refers to the ultimate strain of the tensile elastic segment of fiber-reinforced concrete. The ultimate strain of the tensile plateau segment of fiber-reinforced concrete. The tensile ultimate strain of fiber-reinforced concrete, Tensile strength of fiber-reinforced concrete Yield strain of a tensile steel plate.

[0024] The height of the compression zone of the cross section can be obtained from the equilibrium of forces on the cross section: ; In the formula, This represents the yield strength of the steel plate.

[0025] Deflection The calculation formula is as follows: ; In the formula, This represents the deflection at the end of the elastic working phase with cracks.

[0026] As attached Figure 4 As shown, the upper limit of stiffness in the nonlinear working stage is derived based on the stress-strain distribution diagram of the nonlinear working stage. Stiffness lower limit and ultimate load .

[0027] ; ; ; In the formula, This represents the upper limit of stiffness for a double-plate fiber-reinforced concrete composite beam during the nonlinear operating phase. S 3 represents the shear stiffness during the nonlinear working stage. EI 3-up This represents the upper limit of bending stiffness during the nonlinear operating phase. is the stiffness degradation coefficient of the steel plate; Stiffness lower limit The calculation formula is as follows: ; ; In the formula, EI 3-down This represents the lower limit of bending stiffness during the nonlinear operating stage. ultimate load The calculation formula is as follows: ; ; ; In the formula x 压 The height of the concrete compression zone. x 拉 Height of the tensile zone of the concrete. Upper limit of deflection The calculation formula is as follows: ; In the formula, the upper limit of deflection at the end of the nonlinear working phase is... Lower limit of deflection The calculation formula is as follows: ; In the formula, The lower limit of deflection at the end of the nonlinear working phase.

[0028] After obtaining the stiffness, load, and deflection values ​​for the full-section elastic stage, the cracked elastic working stage, and the nonlinear working stage, the nonlinear response of this double-plate-fiber-reinforced concrete composite beam can be predicted based on the above calculated values. In this field, load-deflection curves are generally used to characterize the response of stressed members.

[0029] The horizontal axis of the load-deflection curve represents the mid-span deflection, and the vertical axis represents the load, which is the load-bearing capacity of the composite beam (excluding external loads). In the load-deflection curve, the stiffness value is presented as a slope, while both deflection and load are represented on the coordinate axes. Therefore, when the form of the load-deflection curve is known, the curve can be determined by specifying the stiffness and load. Since the actual loading process can be considered as static loading, the load value on the load-deflection curve of the member before failure is equal to the external load, and this assumption is also made during prediction.

[0030] The first stage of stress is defined as the elastic stage of the entire cross-section. "First stage" is a common term in this field, referring to the elastic stage of the entire cross-section. In the first stage, stiffness... Starting from the origin, the slope is determined and then extended to the cracking load. or deflection At this point, the initial stiffness is determined.

[0031] The second stage is the elastic working stage with cracks, through yield load. and stiffness The straight line and deflection in the second stage can then be determined. It can also be calculated graphically.

[0032] The third stage is defined as the nonlinear operating phase. In the actual load-deflection curve, the nonlinear phase is an arc with a slope that gradually decreases to 0. During prediction, the range of the arc's extension is determined by using upper and lower stiffness limits through two straight lines or curves to achieve the prediction objective.

[0033] In some embodiments of this application, six types of double-steel-plate fiber-reinforced concrete composite beams with different upper and lower steel plate thicknesses were used to obtain actual load-displacement curves. The geometric dimensions of the composite beams are shown in Table 1, and the mechanical parameters are as follows: Steel plate elastic modulus 200170 , steel plate yield strength 235 , Ultimate strength of steel plate 350 , The yield strain of the tensile steel plate is 0.001175. Fiber-reinforced concrete elastic modulus 42100 , The compressive strength of fiber-reinforced concrete is 134.8. , The tensile strength of fiber-reinforced concrete is 8.2. , The ultimate strain in the elastic tensile section of fiber-reinforced concrete is 0.000193. The ultimate strain of the fiber-reinforced concrete tensile plateau segment is 0.0011. The ultimate tensile strain of fiber-reinforced concrete is 0.0021.

[0034] Table 1. Geometric parameters of double steel plate-fiber reinforced concrete composite beams The stiffness calculated based on S2) Cracking load and deflection As shown in Table 2.

[0035] Table 2. Predicted values ​​for the first stage of double-plate-fiber reinforced concrete composite beams. The stiffness calculated based on step S3) Yield load and deflection As shown in Table 3.

[0036] Table 3. Predicted values ​​for the second stage of double-plate-fiber reinforced concrete composite beams. The stiffness calculated based on step S4) Yield load and deflection As shown in Table 4.

[0037] Table 4. Predicted values ​​for the third stage of double-plate-fiber reinforced concrete composite beams. As attached Figure 5 As shown, the nonlinear response prediction diagram of the double steel plate-fiber reinforced concrete composite beam can be plotted on the load-deflection curve based on the values ​​of the prediction parameters in Tables 2 to 4. Observation Figure 5 It can be seen that the actual experimental results are not much different from the prediction results obtained by the prediction method of the technical solution of this application, and the curve trend of the nonlinear working stage can be included by the prediction value of the third stage.

[0038] For any parts not mentioned in this application, existing technologies may be used or referenced. The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for predicting nonlinear response of a double-steel-plate fiber-reinforced concrete composite beam, characterized by, Includes the following steps: S1) Obtain the material parameters of the double steel plate-fiber reinforced concrete composite beam; The material parameters include: Elastic modulus of steel plate steel plate yield strength Ultimate strength of steel plate Yield strain of tensile steel plate Elastic modulus of fiber-reinforced concrete The compressive strength of fiber-reinforced concrete Tensile strength of fiber-reinforced concrete The ultimate strain of fiber-reinforced concrete in the tensile elastic segment. Ultimate strain of the tensile plateau segment of fiber-reinforced concrete. The ultimate tensile strain of fiber-reinforced concrete Beam span, Upper steel plate thickness, Lower steel plate thickness, core material height, Core material width; S2) Calculate the stiffness of the double-plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. and cracking load And based on stiffness and cracking load Calculate the deflection in the elastic stage of the entire cross section ; S3) Calculate the stiffness of the double-plate-fiber-reinforced concrete composite beam in the elastic working stage with cracks. and yield load And based on stiffness Yield load Cracking load and deflection Calculate the deflection during the elastic working stage of the cracked structure. ; S4) Calculate the upper limit of stiffness of the double steel plate-fiber reinforced concrete composite beam in the nonlinear operating stage. Stiffness lower limit and ultimate load And based on the upper limit of stiffness Ultimate load Yield load and deflection Calculate the upper limit of deflection during the nonlinear working phase. Based on the lower limit of stiffness Ultimate load Yield load and deflection Calculate the lower limit of deflection during the nonlinear operating phase. ; S5) Based on the stiffness, load and deflection calculation results of steps S2) to S4), plot the load-deflection curves of the double steel plate-fiber reinforced concrete composite beam to predict the nonlinear response of the double steel plate-fiber reinforced concrete composite beam.

2. The method for predicting the nonlinear response of a double steel plate-fiber reinforced concrete composite beam according to claim 1, characterized in that, Step S2) calculates the stiffness of the double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. and cracking load And based on stiffness and cracking load Calculate the deflection in the elastic stage of the entire cross section Medium stiffness The calculation formula is as follows: ； ； ； In the formula, The stiffness of the double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. EI 1 represents the flexural stiffness of the section in the elastic stage of the entire cross-section. For the beam span, S 1 represents the shear stiffness of the section in the elastic stage of the entire cross section. The elastic modulus of the steel plate. For the core material width, For the thickness of the upper steel plate, For the thickness of the lower steel plate, d The total thickness of the cross section. To improve the elastic modulus of fiber-reinforced concrete, For core material height; Cracking load The calculation formula is as follows: ； In the formula, The cracking load of a double steel plate-fiber reinforced concrete composite beam in the full-section elastic stage. To enhance the tensile strength of fiber-reinforced concrete; Deflection The calculation formula is as follows: ； In the formula, This represents the deflection of the double steel plate-fiber reinforced concrete composite beam at the end of the full-section elastic stage.

3. The method for predicting the nonlinear response of a double steel plate-fiber reinforced concrete composite beam according to claim 2, characterized in that, Step S3) calculates the stiffness of the double-plate-fiber-reinforced concrete composite beam during the elastic working stage with cracks. and yield load And based on stiffness Yield load Cracking load and deflection Calculate the deflection during the elastic working stage of the cracked structure. Medium stiffness The calculation formula is as follows: ； ； ； In the formula, The stiffness of the double steel plate-fiber reinforced concrete composite beam in the elastic stage of the entire cross section. EI 2 represents the flexural stiffness during the elastic working stage with cracks. S 2 represents the shear stiffness during the elastic working stage with cracks; Yield load The calculation formula is as follows: ； In the formula, x The height of the compression zone of the cross section. This refers to the ultimate strain of the tensile elastic segment of fiber-reinforced concrete. The ultimate strain of the tensile plateau segment of fiber-reinforced concrete. The tensile ultimate strain of fiber-reinforced concrete, Tensile strength of fiber-reinforced concrete; Deflection The calculation formula is as follows: ； In the formula, This represents the deflection at the end of the elastic working phase with cracks.

4. The method for predicting the nonlinear response of a double steel plate-fiber reinforced concrete composite beam according to claim 3, characterized in that, Step S4) calculates the upper limit of stiffness of the double steel plate-fiber reinforced concrete composite beam in the nonlinear working stage. Stiffness lower limit and ultimate load And based on the upper limit of stiffness Ultimate load Yield load and deflection Calculate the upper limit of deflection during the nonlinear working phase. Based on the lower limit of stiffness Ultimate load Yield load and deflection Calculate the lower limit of deflection during the nonlinear operating phase. In the middle, the upper limit of stiffness The calculation formula is as follows: ； ； ； In the formula, This represents the upper limit of stiffness for a double-plate fiber-reinforced concrete composite beam during the nonlinear operating phase. S 3 represents the shear stiffness during the nonlinear working stage. EI 3-up This represents the upper limit of bending stiffness during the nonlinear operating phase. is the stiffness degradation coefficient of the steel plate; Stiffness lower limit The calculation formula is as follows: ； ； In the formula, EI 3-down This represents the lower limit of bending stiffness during the nonlinear operating stage. ultimate load The calculation formula is as follows: ； ； ； In the formula x 压 The height of the concrete compression zone. x 拉 This refers to the height of the tension zone of the concrete. Upper limit of deflection The calculation formula is as follows: ； In the formula, the upper limit of deflection at the end of the nonlinear working phase is... Lower limit of deflection The calculation formula is as follows: ； In the formula, This represents the lower limit of deflection at the end of the nonlinear working phase.

5. A method for predicting the nonlinear response of a double-steel-plate fiber-reinforced concrete composite beam according to any one of claims 1 to 4, characterized in that, Step S5) involves plotting the load-deflection curves of the double-plate-fiber-reinforced concrete composite beam based on the stiffness, load, and deflection calculation results from steps S2) to S4) to predict the nonlinear response of the double-plate-fiber-reinforced concrete composite beam. The nonlinear response of the double-plate-fiber-reinforced concrete composite beam is characterized in the form of deflection-load curves. The step S5) also includes the following steps: S51) with stiffness As the slope of the first stage of the deflection-load curve, the cracking load... The load value corresponding to the end of the first stage is expressed in terms of deflection. The deflection value corresponding to the end point of the first stage; S52) with stiffness As the slope of the second stage of the deflection-load curve, the yield load... The load value corresponding to the end of the second stage is expressed in terms of deflection. The deflection value corresponding to the end point of the second stage; S53) with upper limit of stiffness and lower limit of stiffness These are respectively used as the slopes of the third stage of the deflection-load curve, with the ultimate load as the reference. The load value corresponding to the end of the third stage is the upper limit of deflection. As the upper limit of stiffness Corresponding ultimate load The deflection value; with the lower limit of deflection As the lower limit of stiffness Corresponding ultimate load The deflection value.

6. The method for predicting the nonlinear response of a double-steel-plate fiber-reinforced concrete composite beam according to claim 5, characterized in that, In step S53), the upper limit of stiffness is used. The deflection-load curve for the third stage is plotted when the ultimate load is reached. After that, the load value no longer changes while the deflection value continues to increase until it reaches the lower limit of stiffness. The curves drawn intersect.

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