A CFRP cloth reinforced corrosion reinforced concrete beam bending design method

Abstract

The present application relates to a kind of CFRP cloth reinforced corrosion reinforced concrete beam flexural design method, comprising the following steps: (1) determining the basic parameters of corrosion reinforced concrete beam before CFRP cloth reinforcement and CFRP cloth;(2) calculate the limit parameters of CFRP cloth reinforced corrosion reinforced concrete beam;(3) review limit flexural capacity;(4) determine the failure mode of corrosion reinforced concrete beam after CFRP cloth reinforcement;(5) based on target flexural capacity and target failure mode design required CFRP cloth reinforcement rate.Compared with prior art, the present application has the advantages of simple calculation, strong practicability, and provides support for improving the safety of existing corrosion reinforced concrete beam and prolonging its service life.

Description

Technical Field

[0001] This invention relates to the field of civil engineering technology, and in particular to a flexural design method for CFRP-reinforced corroded reinforced concrete beams. Background Technology

[0002] As the service life of reinforced concrete beams increases, the reinforcing steel bars will corrode. Corrosion leads to the degradation of the mechanical properties of the steel bars and a reduction in the effective cross-sectional area, thus reducing the safety of the corroded reinforced concrete beams. Therefore, carbon fiber reinforced polymer (CFRP) composites have been widely used for the reinforcement of corroded reinforced concrete structures. However, the flexural failure modes of CFRP-reinforced corroded reinforced concrete beams are diverse, making the calculation and design of their flexural bearing capacity more complex.

[0003] Currently, some scholars have used functions based on parameters such as corrosion rate and CFRP reinforcement ratio to correct the flexural capacity of CFRP-reinforced, uncorroded reinforced concrete beams, proposing a calculation formula for the flexural capacity of CFRP-reinforced corroded reinforced concrete beams, and further proposing a design method for the flexural capacity of CFRP-reinforced corroded reinforced concrete beams based on this formula. However, the correction function in this flexural capacity calculation formula needs to be verified experimentally, and its generalizability is questionable. Furthermore, this design method cannot effectively distinguish the changes in failure modes caused by differences in CFRP reinforcement amounts, posing safety hazards. Therefore, to promote the application of CFRP in the reinforcement of corroded reinforced concrete beams, a flexural design method for CFRP-reinforced corroded reinforced concrete beams that can control failure modes is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a CFRP-reinforced reinforced concrete beam bending design method. This method can conveniently and accurately design the required CFRP reinforcement ratio for rusted reinforced concrete beams under different target bending bearing capacities, and control the bending failure mode of CFRP-reinforced reinforced concrete beams.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for flexural design of CFRP-reinforced corroded reinforced concrete beams, comprising the following steps:

[0007] Step 1: Determine the basic parameters of the corroded reinforced concrete beam and the CFRP fabric before reinforcement.

[0008] The basic parameters of the CFRP-reinforced reinforced concrete beam and the CFRP fabric before reinforcement include: cross-sectional width b, cross-sectional height h, effective cross-sectional height h0, concrete strength grade, and concrete compressive strength f. c Concrete tensile strength f t E, the elastic modulus of concrete c The type of deformed or plain reinforcing steel, and the average corrosion rate η of tensile reinforcing steel. s Initial reinforcement area A of tensile reinforcement s0 ; Elastic modulus E of uncorroded steel bars s0 Yield strength f y0 Ultimate strength f u0 Yield strain ε y0 Strengthening strain ε sh0 Ultimate strain ε u0 ; Ultimate tensile strain ε of CFRP cloth fu Elastic modulus E f Initial bending moment M during reinforcement i ε of tensile edge strain in concrete i ; Bending capacity M of rusted reinforced concrete beam before CFRP reinforcement uc The target flexural bearing capacity M of the rusted reinforced concrete beam reinforced with CFRP fabric uf .

[0009] Furthermore, the cross-sectional width b, cross-sectional height h, effective cross-sectional height h0, concrete strength grade, and concrete compressive strength f are also considered. c Concrete tensile strength f t E, the elastic modulus of concrete c Types of deformed or plain round tensile steel bars, and the average corrosion rate η of tensile steel bars. s Initial reinforcement area A of tensile reinforcement s0 The elastic modulus E of uncorroded tensile steel bars s0 Yield strength f y0 Ultimate strength f u0 Yield strain ε y0 Strengthening strain ε sh0 Ultimate strain ε u0 These parameters can be measured according to the methods in GB / T 50784-2013, "Technical Standard for On-site Testing of Concrete Structures". If the mechanical property parameters of uncorroded steel bars are inconvenient to obtain, they can be taken from GB50010-2010 (2015 edition), "Code for Design of Concrete Structures". The elastic modulus E of CFRP fabric... f and ultimate tensile strain ε fu Provided by the manufacturer, or determined according to the "Technical Standard for Engineering Applications of Fiber Reinforced Composite Materials" GB50608-2020; Initial bending moment M iThe strain ε at the edge of the tension zone under the initial bending moment can be estimated based on the actual load. i The flexural bearing capacity M of a CFRP-reinforced reinforced concrete beam before rusting can be estimated according to the provisions of the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" GB50608-2020. uc The target bearing capacity M of the reinforced concrete beam can be calculated using relevant methods (e.g., "Simplified Calculation Method for Bending Capacity of Corroded Reinforced Concrete Beams" (Patent Application No.: CN202011502706.X)); uf Determined based on actual needs.

[0010] Step 2: Calculate the limit parameters of CFRP-reinforced corroded reinforced concrete beams.

[0011] The limit parameters include: limit I reinforcement ratio ρ fsyb Boundary II reinforcement ratio ρ fshb Limit III reinforcement ratio ρ fsub Boundary IV reinforcement ratio ρ fu ; Boundary I relative to the height of the pressure zone ξ fsyb Boundary II relative pressure zone height ξ fshb Boundary III relative pressure zone height ξ fsub Boundary IV relative to the height of the pressure zone ξ fu Boundary I flexural bearing capacity M uf,syb Bending capacity of limit II M uf,shb Bending capacity of limit III M uf,sub Boundary IV flexural bearing capacity M uf,CFRP The boundary I is defined as follows: when the beam fails under bending conditions, the corroded steel reinforcement just begins to yield, the concrete in the compression zone crushes, and the CFRP fabric does not break. The boundary II is defined as follows: when the beam fails under bending conditions, the corroded steel reinforcement just begins to strengthen, the concrete in the compression zone crushes, and the CFRP fabric does not break. The boundary III is defined as follows: when the beam fails under bending conditions, the fracture of the corroded steel reinforcement and the crushing of the concrete in the compression zone occur simultaneously, and the CFRP fabric does not break. The boundary IV is defined as follows: when the beam fails under bending conditions, the fracture of the CFRP fabric and the crushing of the concrete in the compression zone occur simultaneously.

[0012] Furthermore, the limit I reinforcement ratio ρ fsyb ξ, relative height of the pressure zone to boundary I fsyb Boundary I flexural bearing capacity M uf,syb The calculation steps are as follows:

[0013] 1) Induce the strain ε of the corroded steel bars sc =ε yc (η s ), stress σ of corroded steel bars sc =f yc (η s), the edge strain ε of the concrete in the compression zone c t =ε cu , where ε yc (η s ) and f yc (η s ε represents the yield strain and yield stress of the corroded steel reinforcement. cu The ultimate compressive strain of the concrete is expressed as ε, and the strain of the corroded steel reinforcement is expressed as ε. sc and the edge strain ε of the concrete in the compression zone c t Substituting into the deformation compatibility equation, we solve for the relative compression zone height ξ of boundary I. fsyb ;

[0014] 2) The boundary I is relative to the height ξ of the pressure zone. fsyb Substituting into the deformation compatibility equation, solve for the strain ε of the CFRP fabric. f ;

[0015] 3) The relative height ξ of the pressure zone fsyb σ stress of corroded steel bars sc =f yc (η s ) and CFRP cloth strain ε f Substituting into the force equilibrium equation, we can obtain the limit I reinforcement ratio ρ. fsyb ;

[0016] 4) If the calculated limit I reinforcement ratio ρ fsyb ≤0, take ρ fsyb =0, then the limit I flexural bearing capacity M uf,syb =M uc M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fsyb >0, relative pressure zone height ξ fsyb CFRP cloth strain ε f and the limit I reinforcement ratio ρ fsyb Substituting into the moment equilibrium equation, we can calculate M. uf,syb .

[0017] Furthermore, the reinforcement ratio ρ of boundary II fshb Boundary II relative pressure zone height ξ fshb and the limit II flexural bearing capacity M uf,shb The calculation steps are as follows:

[0018] 1) Induce the strain ε of the corroded steel bars sc =ε shc (η s ), stress σ of corroded steel bars sc =f yc (η s), the concrete strain ε at the edge of the compression zone c t =ε cu , where ε shc (η s f represents the strengthening strain of corroded steel bars. yc (η s ε represents the yield stress of the corroded steel reinforcement. cu The ultimate compressive strain of the concrete is expressed as ε, and the strain of the corroded steel reinforcement is expressed as ε. sc and the edge strain ε of the concrete in the compression zone c t Substituting into the deformation compatibility equation, we can solve for the relative compression zone height ξ of boundary II. fshb ;

[0019] 2) The height ξ of boundary II relative to the pressure zone fshb Substituting into the deformation compatibility equation, solve for the strain ε of the CFRP fabric. f ;

[0020] 3) The relative height ξ of the pressure zone fshb σ stress of corroded steel bars sc =f yc (η s ) and CFRP cloth strain ε f Substituting into the force equilibrium equation, we can obtain the reinforcement ratio ρ of limit II. fshb ;

[0021] 4) If the calculated limit II reinforcement ratio ρ fshb ≤0, take ρ fshb =0, then the flexural bearing capacity of limit II is M uf,shb =M uc M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fshb >0, relative pressure zone height ξ fshb CFRP cloth strain ε f and the reinforcement ratio ρ of boundary II fshb Substituting into the moment equilibrium equation, we can calculate M. uf,shb .

[0022] Furthermore, the reinforcement ratio ρ of boundary III fsub Boundary III relative pressure zone height ξ fsub and the limit III flexural bearing capacity M uf,sub The calculation steps are as follows:

[0023] 1) Induce the strain ε of the corroded steel bars sc =ε suc (η s ), stress σ of corroded steel bars sc =f uc (ηs ), the concrete strain ε at the edge of the compression zone c t =ε cu , where ε suc (η s ) and f uc (η s ε represents the ultimate strain and ultimate stress of the corroded steel reinforcement. cu The ultimate compressive strain of the concrete is given. The strain ε of the corroded steel reinforcement is also given. sc and the edge strain ε of the concrete in the compression zone c t Substituting into the deformation compatibility equation, solve for the relative compression zone height ξ at boundary III. fsub ;

[0024] 2) The height ξ of boundary III relative to the pressure zone fsub Substituting into the deformation compatibility equation, solve for the strain ε of the CFRP fabric. f ;

[0025] 3) The relative height ξ of the pressure zone fsub σ stress of corroded steel bars sc =f uc (η s ) and CFRP cloth strain ε f Substituting into the force equilibrium equation, we can obtain the reinforcement ratio ρ of limit III. fsub ;

[0026] 4) If the calculated limit III reinforcement ratio ρ fsub ≤0, take ρ fsub =0, then the flexural bearing capacity of limit III is M uf,sub =M uc M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fsub >0, relative pressure zone height ξ fsub CFRP cloth strain ε f and the reinforcement ratio ρ of boundary III fsub Substituting into the moment equilibrium equation, we can calculate M. uf,sub .

[0027] Furthermore, the limit IV reinforcement ratio ρ fu Boundary IV relative pressure zone height ξ fu and the limit IV flexural bearing capacity M uf,CFRP The calculation steps are as follows:

[0028] 1) Let the strain ε of the CFRP cloth be... f =ε fu ε of concrete strain at the edge of the compression zone c t =εcu , where ε fu For the ultimate tensile strain of CFRP fabric, ε cu Given the ultimate compressive strain of concrete, determine the strain ε of the corroded steel bars based on the deformation compatibility equation and the stress-strain relationship of the corroded steel bars. sc and the stress σ of corroded steel bars sc ; strain ε of CFRP cloth fu and the edge strain ε of the concrete in the compression zone cu Substituting into the deformation compatibility equation, we solve for the relative compression zone height ξ at boundary IV. fu ;

[0029] 2) The strain ε of the CFRP cloth fu σ stress of corroded steel bars sc Relative pressure zone height ξ fu Substituting into the force equilibrium equation, the reinforcement ratio ρ of boundary IV can be obtained. fu ;

[0030] 3) If the calculated limit IV reinforcement ratio ρ fu ≤0, take ρ fu =0, then the limit IV flexural bearing capacity M uf,CFRP =M uc M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fu >0, relative pressure zone height ξ fu CFRP cloth strain ε f and the limit IV reinforcement ratio ρ fu Substituting into the moment equilibrium equation, we can calculate M. uf,CFRP .

[0031] Step 3: Verify the limit bending capacity.

[0032] The verification of the limit flexural bearing capacity includes:

[0033] 1) If ξ fu >ξ fsyb Take M uf,syb =M uf,shb =M uf,sub =M uc ;

[0034] 2) If ξ fsyb ≥ξ fu >ξ fshb Take M uf,shb =M uf,sub =M uc ;

[0035] 3) If ξ fshb ≥ξ fu >ξ fsub Take Muf,sub =M uc .

[0036] The limit flexural capacity reviewed in this step can be determined to have some limits that do not exist. Therefore, the limit values ​​of these non-existent limits can be directly specified for use in step four to determine the failure mode.

[0037] Step 4: Determine the bending failure mode of the CFRP-reinforced reinforced concrete beam.

[0038] The flexural failure modes of CFRP-reinforced reinforced concrete beams with corrosion include:

[0039] If M uf ≤M uf,CFRP If the result is positive, it is determined to be mode ⑤, that is, the stress of CFRP bracing, corroded steel bars and concrete in the compression zone is undetermined when the flexural failure occurs.

[0040] If M uf >M uf,CFRP And M uf >M uf,syb If so, it is determined to be mode ①, that is, when the CFRP fabric is not broken during bending failure, the rusted steel bar is elastic, and the concrete in the compression zone is crushed.

[0041] If M uf >M uf,CFRP And M uf,syb ≥M uf >M uf,shb If so, it is determined to be mode ②, that is, when the CFRP fabric is not broken, the corroded steel bars yield, and the concrete in the compression zone is crushed when the bending failure occurs.

[0042] If M uf >M uf,CFRP And M uf,shb ≥M uf >M uf,sub If so, it is determined to be mode ③, that is, when the CFRP fabric is not broken during bending failure, the rusted steel reinforcement is strengthened, and the concrete in the compression zone is crushed.

[0043] If M uf >M uf,CFRP And M uf,sub ≥M uf >M uc If the condition is met, it is determined to be mode ④, that is, when the CFRP fabric fails under bending, the corroded steel bar fails, and the concrete in the compression zone is crushed.

[0044] Step 5: Determine the target bending failure mode based on actual needs, and design the required CFRP fabric reinforcement ratio based on the target failure mode and bending bearing capacity.

[0045] The CFRP reinforcement ratio for corroded reinforced concrete beams includes: the CFRP reinforcement ratio ρ of corroded reinforced concrete beams under Mode ①, Mode ②, Mode ③, Mode ④, and Mode ⑤. f .

[0046] In this invention, the CFRP fabric reinforcement ratio ρ corresponding to mode ① is... f The calculation steps are as follows:

[0047] 1) Let the concrete strain ε at the edge of the compression zone of the section be... c t =ε cu , where ε cu Given the ultimate compressive strain of concrete, the strain ε of the corroded steel reinforcement related to the relative height of the compression zone ξ can be obtained according to the deformation compatibility equation. sc (ξ) and CFRP strain ε f (ξ);

[0048] 2) The strain ε of the corroded steel bar sc Substituting (ξ) into the stress-strain relationship of the corroded steel bar, we obtain the stress σ of the corroded steel bar. sc (ξ), the stress σ of the corroded steel bar sc Substituting (ξ) into the moment equilibrium equation, we obtain a cubic equation in one variable concerning the relative height of the compression zone ξ. Solving this equation, we take ξ > ξ. fsyb The smaller solution within the range is taken as the value of ξ;

[0049] 3) The relative height of the compression zone ξ and the CFRP strain ε f (ξ) and stress σ of corroded steel bars sc (ξ) Substitute into the force balance equation to solve for the CFRP reinforcement ratio corresponding to mode ①.

[0050] The corresponding CFRP fabric reinforcement ratio ρ under mode ② f The calculation steps are as follows:

[0051] 1) Let the concrete strain ε at the edge of the compression zone of the section be... c t =ε cu , where ε cu Given the ultimate compressive strain of concrete, the strain ε of the corroded steel reinforcement related to the relative height of the compression zone ξ can be obtained according to the deformation compatibility equation. sc (ξ) and CFRP strain ε f (ξ);

[0052] 2) Let the stress σ of the corroded steel bar be... sc =f yc (η s ), where f yc (η sThe stress σ of the corroded steel bar is the yield stress; sc Substituting into the moment equilibrium equation, we obtain a quadratic equation in one variable concerning the relative height of the compression zone ξ. Solving this equation, we take ξ as... fsyb ≥ξ>ξ fshb The smaller solution within the range is taken as the value of ξ;

[0053] 3) The relative height of the compression zone ξ and the strain ε of the CFRP cloth are calculated. f (ξ) and stress σ of corroded steel bars sc (ξ) Substitute into the force balance equation to solve the CFRP reinforcement ratio corresponding to mode ②.

[0054] The calculation steps for the CFRP reinforcement ratio corresponding to the target flexural bearing capacity of the reinforced concrete beam after reinforcement, under the failure mode of mode ③, are as follows:

[0055] 1) Let the concrete strain ε at the edge of the compression zone of the section be... c t =ε cu , where ε cu Given the ultimate compressive strain of concrete, the strain ε of the corroded steel reinforcement related to the relative height of the compression zone ξ can be obtained according to the deformation compatibility equation. sc (ξ) and CFRP strain ε f (ξ);

[0056] 2) The strain ε of the corroded steel bar sc Substituting (ξ) into the stress-strain relationship of the corroded steel bar, we obtain the stress σ of the corroded steel bar. sc (ξ), the stress σ of the corroded steel bar sc Substituting (ξ) into the moment equilibrium equation, we obtain a cubic equation in one variable concerning the relative height of the compression zone ξ. Solving this equation, we take ξ as... fshb ≥ξ>ξ fsub The smaller solution within the range is taken as the value of ξ;

[0057] 3) The relative height of the compression zone ξ and the strain ε of the CFRP cloth are calculated. f (ξ) and stress σ of corroded steel bars sc (ξ) Substitute into the force balance equation to solve for the CFRP reinforcement ratio corresponding to mode ③.

[0058] CFRP fabric reinforcement ratio ρ in mode ④ f =min{ρ f1 , ρ f2}, where ρ f1 The reinforcement ratio of CFRP fabric is defined as follows: when the reinforcing steel breaks, the CFRP fabric is in an elastic state, and the concrete is not crushed; ρ f2 The reinforcement ratio of CFRP fabric is defined as follows: after the steel bar breaks, the CFRP fabric is in an elastic state, and the concrete is crushed.

[0059] CFRP fabric reinforcement rate ρ under mode ⑤ f1 With ρ f2 The calculation steps are as follows:

[0060] 1) Let the relative pressure zone height ξ = ξ fsub ε strain of corroded steel bars sc =ε suc (η s ), where ξ fsub ε represents the relative height of the pressure zone of boundary IV. suc (η s The strain ε of the CFRP is the ultimate strain of the corroded steel reinforcement. The strain value ε is obtained from the deformation compatibility equation. f ;

[0061] 2) Let the stress σ of the corroded steel bar be... sc =f uc (η s ), where f uc (η s Let ρ be the ultimate stress of the corroded steel bar. Taking the moment of the resultant force of the steel bar tension and the CFRP bracing about the point of compressive force on the concrete, we can solve for ρ. f1 As shown in the following formula:

[0062]

[0063] 3) Let σ sc =0, substituting into the force equilibrium equation, we obtain the relative compression zone height ξ, and then according to the bending moment equilibrium equation and M uf The value of ρ is calculated. f2 value.

[0064] The failure mode of the CFRP-reinforced reinforced concrete beam is the CFRP reinforcement ratio ρ corresponding to the target flexural bearing capacity under mode ⑤. f =ρ fu , where ρ fu The limit IV reinforcement ratio.

[0065] Furthermore, in steps two through five above, the force balance equations involved are:

[0066] α1f c bξh=E f ε f A f +σ sc A s0 (1-η s )

[0067] In the formula, α1 is the equivalent rectangular coefficient, which is 1.0 when the concrete strength grade is less than or equal to C50.

[0068] The moment equilibrium equations involved are:

[0069] M uf =α1f c bξh(h0-0.5ξh)+E f ε f A f (h-h0)

[0070] =α1f c bξh(h0-0.5ξh)+[α1f c bξh-σ sc (ξ)A s0 (1-η s )](h-h0)

[0071] The deformation compatibility equations involved are:

[0072]

[0073] In the formula, β1 is the equivalent rectangular coefficient, which is 0.8 when the concrete strength grade is less than or equal to C50; x n This represents the actual strain distribution height.

[0074] The formula for calculating the stress-strain relationship of the corroded steel bars involved is as follows:

[0075]

[0076] The formula for calculating the elastic modulus of the corroded steel bars involved is as follows:

[0077] E sc =E s0

[0078] The formula for calculating the yield stress of the corroded steel bars involved is as follows:

[0079]

[0080] The formula for calculating the ultimate stress of the corroded steel bars involved is as follows:

[0081]

[0082] The formula for calculating the yield strain of the corroded steel bars involved is as follows:

[0083]

[0084] The formula for calculating the strengthening strain of corroded steel bars is as follows:

[0085]

[0086] The formula for calculating the ultimate strain of the corroded steel bars involved is as follows:

[0087]

[0088] The formula for calculating the reinforcing modulus of corroded steel bars is as follows:

[0089]

[0090] The flexural design method for CFRP-reinforced corroded reinforced concrete beams provided by this invention has at least the following advantages compared to existing technologies:

[0091] This invention considers the influence of CFRP reinforcement on the failure mode and flexural capacity of corroded reinforced concrete beams, and proposes the concepts of limit reinforcement ratio and limit flexural capacity. Therefore, the CFRP reinforcement ratio can be designed based on the target flexural capacity and target flexural failure mode, or the flexural capacity and flexural failure mode of corroded reinforced concrete beams can be controlled by adjusting the CFRP reinforcement ratio. The method is conceptually clear, computationally simple, and highly practical, providing support for improving the safety of existing corroded reinforced concrete beams and extending their service life. Attached Figure Description

[0092] Figure 1 This is a schematic diagram of the stress distribution of the CFRP-reinforced corroded reinforced concrete beam in the flexural design method of the CFRP-reinforced corroded reinforced concrete beam in the embodiment. Sub-figure (a) is the stress distribution diagram of the CFRP-reinforced corroded reinforced concrete beam in the flexural section, sub-figure (b) is the equivalent stress distribution diagram of the CFRP-reinforced corroded reinforced concrete beam in the flexural section, and sub-figure (c) is the strain distribution diagram of the CFRP-reinforced corroded reinforced concrete beam in the flexural section.

[0093] Figure 2 This example illustrates the CFRP fabric-reinforced rusted reinforced concrete beam flexural design method, including the CFRP failure mode and strain distribution of the CFRP fabric-reinforced rusted reinforced concrete beam under elastic conditions.

[0094] Figure 3 This example illustrates the failure mode and strain distribution of CFRP-reinforced reinforced concrete beams reinforced with CFRP fabric during tensile fracture, as described in the CFRP fabric-reinforced flexural design method for CFRP-reinforced corroded reinforced concrete beams. Detailed Implementation

[0095] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0096] Example

[0097] This invention relates to a flexural design method for CFRP-reinforced corroded reinforced concrete beams, combined with... Figures 1-3 As shown, it includes the following steps:

[0098] S1: Determine the basic parameters of the corroded reinforced concrete beam and the CFRP fabric before reinforcement.

[0099] The basic parameters of the CFRP-reinforced reinforced concrete beam and the CFRP fabric before reinforcement include: cross-sectional width b, cross-sectional height h, effective cross-sectional height h0, concrete strength grade, and concrete compressive strength f. c Concrete tensile strength f t E, the elastic modulus of concrete c The type of deformed or plain reinforcing steel, and the average corrosion rate η of tensile reinforcing steel. s Initial reinforcement area A of tensile reinforcement s0 ; Elastic modulus E of uncorroded steel bars s0 Yield strength f y0 Ultimate strength f u0 Yield strain ε y0 Strengthening strain ε sh0 Ultimate strain ε u0 ; Ultimate tensile strain ε of CFRP cloth fu Elastic modulus E f Initial bending moment M during reinforcement i ε of tensile edge strain in concrete i ; Bending capacity M of rusted reinforced concrete beam before CFRP reinforcement uc The target flexural bearing capacity M of the rusted reinforced concrete beam reinforced with CFRP fabric uf .

[0100] Furthermore, the cross-sectional width b, cross-sectional height h, effective cross-sectional height h0, concrete strength grade, and concrete compressive strength f are also considered. c Concrete tensile strength f t E, the elastic modulus of concrete c Types of deformed or plain round tensile steel bars, and the average corrosion rate η of tensile steel bars. s Initial reinforcement area A of tensile reinforcement s0 The elastic modulus E of uncorroded tensile steel bars s0 Yield strength f y0 Ultimate strength f u0 Yield strain ε y0 Strengthening strain ε sh0 Ultimate strain ε u0These parameters can be measured according to the methods in GB / T 50784-2013, "Technical Standard for On-site Testing of Concrete Structures". If the mechanical property parameters of uncorroded steel bars are inconvenient to obtain, they can be taken from GB50010-2010 (2015 edition), "Code for Design of Concrete Structures". The elastic modulus E of CFRP fabric... f and ultimate tensile strain ε fu Provided by the manufacturer, or determined according to the "Technical Standard for Engineering Applications of Fiber Reinforced Composite Materials" GB50608-2020; Initial bending moment M i The strain ε at the edge of the tension zone under the initial bending moment can be estimated based on the actual load. i The flexural bearing capacity M of a CFRP-reinforced reinforced concrete beam before rusting can be estimated according to the provisions of the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" GB50608-2020. uc The target bearing capacity M of the reinforced concrete beam can be calculated using relevant methods (e.g., "Simplified Calculation Method for Bending Capacity of Corroded Reinforced Concrete Beams" (Patent Application No.: CN202011502706.X)); uf Determined based on actual needs.

[0101] S2: Calculate the limit parameters of CFRP-reinforced corroded reinforced concrete beams.

[0102] The limit parameters include: limit I reinforcement ratio ρ fsyb Boundary II reinforcement ratio ρ fshb Limit III reinforcement ratio ρ fsub Boundary IV reinforcement ratio ρ fu ; Boundary I relative to the height of the pressure zone ξ fsyb Boundary II relative pressure zone height ξ fshb Boundary III relative pressure zone height ξ fsub Boundary IV relative to the height of the pressure zone ξ fu Boundary I flexural bearing capacity M uf,syb Bending capacity of limit II M uf,shb Bending capacity of limit III M uf,sub Boundary IV flexural bearing capacity M uf,CFRP .

[0103] Furthermore, the limit I reinforcement ratio ρ fsyb ξ, relative height of the pressure zone to boundary I fsyb Boundary I flexural bearing capacity M uf,syb The calculation steps are as follows:

[0104] 1) Induce the strain ε of the corroded steel bars sc =ε yc (η s ), stress σ of corroded steel bars sc =fyc (η s ), the edge strain ε of the concrete in the compression zone c t =ε cu , where ε yc (η s ) and f yc (η s ε represents the yield strain and yield stress of the corroded steel reinforcement. cu The ultimate compressive strain of the concrete is expressed as ε, and the strain of the corroded steel reinforcement is expressed as ε. sc and the edge strain ε of the concrete in the compression zone c t Substituting into the deformation compatibility equation, we solve for the relative compression zone height ξ of boundary I. fsyb ;

[0105] 2) The boundary I is relative to the height ξ of the pressure zone. fsyb Substituting into the deformation compatibility equation, solve for the strain ε of the CFRP fabric. f ;

[0106] 3) The relative height ξ of the pressure zone fsyb σ stress of corroded steel bars sc =f yc (η s ) and CFRP cloth strain ε f Substituting into the force equilibrium equation, we can obtain the limit I reinforcement ratio ρ. fsyb ;

[0107] 4) If the calculated limit I reinforcement ratio ρ fsyb ≤0, take ρ fsyb =0, then the limit I flexural bearing capacity M uf,syb =M uc M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fsyb >0, relative pressure zone height ξ fsyb CFRP cloth strain ε f and the limit I reinforcement ratio ρ fsyb Substituting into the moment equilibrium equation, we can calculate M. uf,syb .

[0108] Furthermore, the reinforcement ratio ρ of boundary II fshb Boundary II relative pressure zone height ξ fshb and the limit II flexural bearing capacity M uf,shb The calculation steps are as follows:

[0109] 1) Induce the strain ε of the corroded steel bars sc =ε shc (η s ), stress σ of corroded steel bars sc =fyc (η s ), the concrete strain ε at the edge of the compression zone c t =ε cu , where ε shc (η s f represents the strengthening strain of corroded steel bars. yc (η s ε represents the yield stress of the corroded steel reinforcement. cu The ultimate compressive strain of the concrete is expressed as ε, and the strain of the corroded steel reinforcement is expressed as ε. sc and the edge strain ε of the concrete in the compression zone c t Substituting into the deformation compatibility equation, we can solve for the relative compression zone height ξ of boundary II. fshb ;

[0110] 2) The height ξ of boundary II relative to the pressure zone fshb Substituting into the deformation compatibility equation, solve for the strain ε of the CFRP fabric. f ;

[0111] 3) The relative height ξ of the pressure zone fshb σ stress of corroded steel bars sc =f yc (η s ) and CFRP cloth strain ε f Substituting into the force equilibrium equation, we can obtain the reinforcement ratio ρ of limit II. fshb ;

[0112] 4) If the calculated limit II reinforcement ratio ρ fshb ≤0, take ρ fshb =0, then the flexural bearing capacity of limit II is M uf,shb =M uc M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fshb >0, relative pressure zone height ξ fshb CFRP cloth strain ε f and the reinforcement ratio ρ of boundary II fshb Substituting into the moment equilibrium equation, we can calculate M. uf,shb .

[0113] Furthermore, the reinforcement ratio ρ of boundary III fsub Boundary III relative pressure zone height ξ fsub and the limit III flexural bearing capacity M uf,sub The calculation steps are as follows:

[0114] 1) Induce the strain ε of the corroded steel bars sc =ε suc (η s ), stress σ of corroded steel bars sc=f uc (η s ), the concrete strain ε at the edge of the compression zone c t =ε cu , where ε suc (η s ) and f uc (η s ε represents the ultimate strain and ultimate stress of the corroded steel reinforcement. cu The ultimate compressive strain of the concrete is given. The strain ε of the corroded steel reinforcement is also given. sc and the edge strain ε of the concrete in the compression zone c t Substituting into the deformation compatibility equation, solve for the relative compression zone height ξ at boundary III. fsub ;

[0115] 2) The height ξ of boundary III relative to the pressure zone fsub Substituting into the deformation compatibility equation, solve for the strain ε of the CFRP fabric. f ;

[0116] 3) The relative height ξ of the pressure zone fsub σ stress of corroded steel bars sc =f uc (η s ) and CFRP cloth strain ε f Substituting into the force equilibrium equation, we can obtain the reinforcement ratio ρ of limit III. fsub ;

[0117] 4) If the calculated limit III reinforcement ratio ρ fsub ≤0, take ρ fsub =0, then the flexural bearing capacity of limit III is M uf,sub =M uc M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fsub >0, relative pressure zone height ξ fsub CFRP cloth strain ε f and the reinforcement ratio ρ of boundary III fsub Substituting into the moment equilibrium equation, we can calculate M. uf,sub .

[0118] Furthermore, the limit IV reinforcement ratio ρ fu Boundary IV relative pressure zone height ξ fu and the limit IV flexural bearing capacity M uf,CFRP The calculation steps are as follows:

[0119] 1) Let the strain ε of the CFRP cloth be... f =ε fu ε of concrete strain at the edge of the compression zone ct =ε cu , where ε fu For the ultimate tensile strain of CFRP fabric, ε cu Given the ultimate compressive strain of concrete, determine the strain ε of the corroded steel bars based on the deformation compatibility equation and the stress-strain relationship of the corroded steel bars. sc and the stress σ of corroded steel bars sc ; strain ε of CFRP cloth fu and the edge strain ε of the concrete in the compression zone cu Substituting into the deformation compatibility equation, we solve for the relative compression zone height ξ at boundary IV. fu ;

[0120] 2) The strain ε of the CFRP cloth fu σ stress of corroded steel bars sc Relative pressure zone height ξ fu Substituting into the force equilibrium equation, the reinforcement ratio ρ of boundary IV can be obtained. fu ;

[0121] 3) If the calculated limit IV reinforcement ratio ρ fu ≤0, take ρ fu =0, then the limit IV flexural bearing capacity M uf,CFRP =M uc M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fu >0, relative pressure zone height ξ fu CFRP cloth strain ε f and the limit IV reinforcement ratio ρ fu Substituting into the moment equilibrium equation, we can calculate M. uf,CFRP .

[0122] S3: The limit flexural bearing capacity is obtained by judgment.

[0123] The verification of the limit flexural bearing capacity includes:

[0124] 1) If ξ fu >ξ fsyb Take M uf,syb =M uf,shb =M uf,sub =M uc ;

[0125] 2) If ξ fsyb ≥ξ fu >ξ fshb Take M uf,shb =M uf,sub =M uc ;

[0126] 3) If ξ fshb ≥ξ fu >ξfsub Take M uf,sub =M uc .

[0127] S4: Determine the flexural failure mode of a CFRP-reinforced reinforced concrete beam under flexural stress.

[0128] The flexural failure modes of CFRP-reinforced reinforced concrete beams with corrosion include:

[0129] If M uf ≤M uf,CFRP If so, it is determined to be pattern ⑤.

[0130] If M uf >M uf,CFRP And M uf >M uf,syb If so, it is determined to be pattern ①;

[0131] If M uf >M uf,CFRP And M uf,syb ≥M uf >M uf,shb If so, it is determined to be pattern ②;

[0132] If M uf >M uf,CFRP And M uf,shb ≥M uf >M uf,sub If so, it is determined to be pattern ③;

[0133] If M uf >M uf,CFRP And M uf,sub ≥M uf >M uc If so, it is determined to be pattern ④.

[0134] S5: Determine the target bending failure mode based on actual needs, and design the required CFRP fabric reinforcement rate based on the target failure mode and bending bearing capacity.

[0135] The CFRP reinforcement ratio for corroded reinforced concrete beams includes: the CFRP reinforcement ratio ρ of corroded reinforced concrete beams under Mode ①, Mode ②, Mode ③, Mode ④, and Mode ⑤. f .

[0136] In this invention, the CFRP fabric reinforcement ratio ρ corresponding to mode ① is... f The calculation steps are as follows:

[0137] 1) Let the concrete strain ε at the edge of the compression zone of the section be... c t =ε cu , where ε cuGiven the ultimate compressive strain of concrete, the strain ε of the corroded steel reinforcement related to the relative height of the compression zone ξ can be obtained according to the deformation compatibility equation. sc (ξ) and CFRP strain ε f (ξ);

[0138] 3) The strain ε of the corroded steel bar sc Substituting (ξ) into the stress-strain relationship of the corroded steel bar, we obtain the stress σ of the corroded steel bar. sc (ξ), the stress σ of the corroded steel bar sc Substituting (ξ) into the moment equilibrium equation, we obtain a cubic equation in one variable concerning the relative height of the compression zone ξ. Solving this equation, we take ξ > ξ. fsyb The smaller solution within the range is taken as the value of ξ;

[0139] 3) The relative height of the compression zone ξ and the CFRP strain ε f (ξ) and stress σ of corroded steel bars sc (ξ) Substitute into the force balance equation to solve for the CFRP reinforcement ratio corresponding to mode ①.

[0140] The corresponding CFRP fabric reinforcement ratio ρ under mode ② f The calculation steps are as follows:

[0141] 1) Let the concrete strain ε at the edge of the compression zone of the section be... c t =ε cu , where ε cu Given the ultimate compressive strain of concrete, the strain ε of the corroded steel reinforcement related to the relative height of the compression zone ξ can be obtained according to the deformation compatibility equation. sc (ξ) and CFRP strain ε f (ξ);

[0142] 2) Let the stress σ of the corroded steel bar be... sc =f yc (η s ), where f yc (η s The stress σ of the corroded steel bar is the yield stress; sc Substituting into the moment equilibrium equation, we obtain a quadratic equation in one variable concerning the relative height of the compression zone ξ. Solving this equation, we take ξ as... fsyb ≥ξ>ξ fshb The smaller solution within the range is taken as the value of ξ;

[0143] 3) The relative height of the compression zone ξ and the strain ε of the CFRP cloth are calculated. f (ξ) and stress σ of corroded steel bars sc (ξ) Substitute into the force balance equation to solve the CFRP reinforcement ratio corresponding to mode ②.

[0144] The calculation steps for the CFRP reinforcement ratio corresponding to the target flexural bearing capacity of the reinforced concrete beam after reinforcement, under the failure mode of mode ③, are as follows:

[0145] 1) Let the concrete strain ε at the edge of the compression zone of the section be... c t =ε cu , where ε cu Given the ultimate compressive strain of concrete, the strain ε of the corroded steel reinforcement related to the relative height of the compression zone ξ can be obtained according to the deformation compatibility equation. sc (ξ) and CFRP strain ε f (ξ);

[0146] 2) The strain ε of the corroded steel bar sc Substituting (ξ) into the stress-strain relationship of the corroded steel bar, we obtain the stress σ of the corroded steel bar. sc (ξ), the stress σ of the corroded steel bar sc Substituting (ξ) into the moment equilibrium equation, we obtain a cubic equation in one variable concerning the relative height of the compression zone ξ. Solving this equation, we take ξ as... fshb ≥ξ>ξ fsub The smaller solution within the range is taken as the value of ξ;

[0147] 3) The relative height of the compression zone ξ and the strain ε of the CFRP cloth are calculated. f (ξ) and stress σ of corroded steel bars sc (ξ) Substitute into the force balance equation to solve for the CFRP reinforcement ratio corresponding to mode ③.

[0148] CFRP fabric reinforcement ratio ρ in mode ④ f =min{ρ f1 , ρ f2}, where ρ f1 The reinforcement ratio of CFRP fabric is defined as follows: when the reinforcing steel breaks, the CFRP fabric is in an elastic state, and the concrete is not crushed; ρ f2 The reinforcement ratio of CFRP fabric is defined as follows: after the steel bar breaks, the CFRP fabric is in an elastic state, and the concrete is crushed.

[0149] CFRP fabric reinforcement rate ρ under mode ⑤ f1 With ρ f2 The calculation steps are as follows:

[0150] 3) Let the relative pressure zone height ξ = ξ fsub ε strain of corroded steel bars sc =ε suc (η s ), where ξ fsub ε represents the relative height of the pressure zone of boundary IV. suc (η s The strain ε of the CFRP is the ultimate strain of the corroded steel reinforcement. The strain value ε is obtained from the deformation compatibility equation. f;

[0151] 4) Increase the stress σ of the corroded steel bars sc =f uc (η s ), where f uc (η s Let ρ be the ultimate stress of the corroded steel bar. Taking the moment of the resultant force of the steel bar tension and the CFRP bracing about the point of compressive force on the concrete, we can solve for ρ. f1 As shown in the following formula:

[0152]

[0153] 3) Let σ sc =0, substituting into the force equilibrium equation, we obtain the relative compression zone height ξ, and then according to the bending moment equilibrium equation and M uf The value of ρ is calculated. f2 value.

[0154] The failure mode of the CFRP-reinforced reinforced concrete beam is the CFRP reinforcement ratio ρ corresponding to the target flexural bearing capacity under mode ⑤. f =ρ fu , where ρ fu The limit IV reinforcement ratio.

[0155] Furthermore, in the processes S2 to S5 described above, the force balance equations involved are:

[0156] α1f c bξh=E f ε f A f +σ sc A s0 (1-η s )

[0157] In the formula, α1 is the equivalent rectangular coefficient, which is 1.0 when the concrete strength grade is less than or equal to C50.

[0158] The moment equilibrium equations involved are:

[0159] M uf =α1f c bξh(h0-0.5ξh)+E f ε f A f (h-h0)

[0160] =α1f c bξh(h0-0.5ξh)+[α1f c bξh-σ sc (ξ)A s0 (1-η s )](h-h0)

[0161] The deformation compatibility equations involved are:

[0162]

[0163] In the formula, β1 is the equivalent rectangular coefficient, which is 0.8 when the concrete strength grade is less than or equal to C50; x n This represents the actual strain distribution height.

[0164] The formula for calculating the stress-strain relationship of the corroded steel bars involved is as follows:

[0165]

[0166] The formula for calculating the elastic modulus of the corroded steel bars involved is as follows:

[0167] E sc =E s0

[0168] The formula for calculating the yield stress of the corroded steel bars involved is as follows:

[0169]

[0170] The formula for calculating the ultimate stress of the corroded steel bars involved is as follows:

[0171]

[0172] The formula for calculating the yield strain of the corroded steel bars involved is as follows:

[0173]

[0174] The formula for calculating the strengthening strain of corroded steel bars is as follows:

[0175]

[0176] The formula for calculating the ultimate strain of the corroded steel bars involved is as follows:

[0177]

[0178] The formula for calculating the reinforcing modulus of corroded steel bars is as follows:

[0179]

[0180] This embodiment further illustrates the above-described method of the present invention through actual implementation.

[0181] In this embodiment, a laboratory in Shanghai obtained a corroded reinforced concrete beam (numbered L1) using an electrolytic corrosion accelerated corrosion method. The target bearing capacity of the CFRP-reinforced corroded reinforced concrete beam was calculated to be M. ufThe required CFRP fabric reinforcement amount when the strength is 25 kN·m. The specific steps of this method include the following:

[0182] (1) Determine the basic parameters of the rusted reinforced concrete beam and the CFRP fabric before reinforcement.

[0183] According to the method described in GB / T 50784-2013 "Technical Standard for On-site Testing of Concrete Structures", the cross-section of the corroded reinforced concrete beam was measured to be rectangular, with a cross-section width b = 150 mm, a cross-section height h = 200 mm, and an effective cross-section height h0 = 165 mm. The concrete compressive strength f was measured. c =22.9 N / mm 2 Concrete tensile strength f t =2.29 N / mm 2 The measured number of tensile reinforcing bars was 2, with a diameter of 14mm, and an average corrosion rate η. s =0.087; The elastic modulus E of the uncorroded tensile steel bar was measured. s0 =210000MPa, yield strength f y0 =380MPa, ultimate strength f u0 =580MPa, yield strain ε y0 =0.001856, strengthening strain ε sh0 =0.023, ultimate strain ε u0 =0.143; Referring to the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials (GB50608-2020)", the elastic modulus E of CFRP fabric is... f =261800MPa, ultimate tensile strain ε of CFRP cloth fu =0.01. Initial bending moment M i The estimated value is 8.48 kN·m. Referring to the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials (GB50608-2020)", the initial tensile strain at the tensile edge of the concrete during reinforcement is calculated to be ε. i =0.001. The flexural bearing capacity of the corroded reinforced concrete beam is M. uc =17.30 kN·m, the target flexural bearing capacity after reinforcement is M uf =25kN·m.

[0184] (2) Calculate the limit parameters for CFRP-reinforced corroded reinforced concrete beams. Specifically:

[0185] 21) Calculate the reinforcement ratio ρ of limit I. fsyb The relative height of the pressure zone I is ξ fsyb Boundary I flexural bearing capacity M uf,syb .

[0186] The corrosion rate of steel bars is η s=0.087, at this point the yield stress and yield strain of the corroded steel bar are:

[0187]

[0188] At this point, the relative height of the pressure zone corresponding to boundary I is:

[0189]

[0190] CFRP strain is:

[0191]

[0192] The reinforcement rate corresponding to limit I is:

[0193]

[0194] At this point, the flexural bearing capacity corresponding to boundary I is:

[0195] M uf,syb =α1f c bξ fsyb h(h0-0.5ξ fsyb h)+E f ε f ρ fsyb bh(h-h0)=42.11kN·m

[0196] 22) Calculate the reinforcement ratio ρ of limit II fshb The relative height of the pressure zone of boundary II ξ fshb Bending capacity of limit II M uf,shb .

[0197] The corrosion rate of steel bars is η s =0.087, let the strengthening strain of the corroded steel be:

[0198]

[0199] At this point, the relative height of the compression zone corresponding to boundary II is:

[0200]

[0201] CFRP strain is:

[0202]

[0203] The reinforcement rate corresponding to boundary II is:

[0204]

[0205] ρ fsub If less than zero, take ρ. fsub =0. Muf,sub =M uc =17.30 kN·m.

[0206] 23) Calculate the reinforcement ratio ρ of limit III fsub The relative height of the pressure zone of boundary III ξ fsub Bending capacity of limit III M uf,sub .

[0207] The corrosion rate of steel bars is η s =0.087, let the ultimate strain and ultimate stress of the corroded steel be:

[0208]

[0209] At this point, the relative height of the compression zone corresponding to boundary III is:

[0210]

[0211] CFRP strain is:

[0212]

[0213] The reinforcement rate corresponding to limit III is:

[0214]

[0215] ρ fsub If less than zero, take ρ. fsub =0. Take ρ fshb =0. M uf,sub =M uc =17.30 kN·m.

[0216] 24) Calculate the reinforcement ratio ρ of limit IV. fu Relative pressure zone height ξ fu and flexural bearing capacity M uf,CFRP .

[0217] At this point, the relative height of the compression zone corresponding to boundary IV is:

[0218]

[0219] The strain of the steel reinforcement is:

[0220]

[0221] At this point, the steel reinforcement is in a yielding state, and the reinforcement ratio corresponding to boundary IV is:

[0222]

[0223] At this point, the flexural bearing capacity corresponding to boundary IV is:

[0224] M uf,CFRP =α1f c bξ fu h(h0-0.5ξ fu h)+E f ε f ρ fu bh(h-h0)=19.318kN·m

[0225] (3) Verify the limit flexural bearing capacity

[0226] At this time ξ fyb ≥ξ fu >ξ fshb M uf,shb =M uf,sub =M uc .

[0227] (4) Determine the failure mode of CFRP-reinforced reinforced concrete beams after corrosion.

[0228] The general formula for determining CFRP corruption mode is as follows:

[0229] Calculate M uf >M uf,CFRP The destruction modes are as follows:

[0230] a) When M uf >M uf,syb At this time, it is the destruction mode ①;

[0231] b) When M uf,syb ≥M uf >M uf,shb At this time, it is destruction mode ②;

[0232] c) When M uf,shb ≥M uf >M uf,sub At this time, it is the destruction mode ③;

[0233] d) When M uf,sub ≥M uf >M uc At this time, it is the destruction mode ④.

[0234] At this time M uf,syb ≥M uf >M uf,shb The failure mode of the reinforced concrete beam after reinforcement and corrosion is mode ②. At this time, the CFRP is elastic, the concrete is crushed, and the steel bars yield.

[0235] (5) Design the required CFRP reinforcement ratio based on the target flexural bearing capacity and target failure mode.

[0236] When the steel reinforcement is in a yielding state, the moment equilibrium equation is as follows, which is a quadratic equation in ξ.

[0237] M uf =α1f c bξh(h0-0.5ξh)+[α1f c bξh-f yc (η s A s0 (1-η s )](h-h0)

[0238] The equation is simplified as follows:

[0239] ξ 2 -2ξ+0.4178=0

[0240] CFRP strain ε f As shown below:

[0241]

[0242]

[0243] Based on the above analysis, it can be concluded that when the effective CFRP reinforcement rate is 0.001066, the target flexural bearing capacity requirement after reinforcement is met for the corroded beam L1.

[0244] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for flexural design of CFRP-reinforced corroded reinforced concrete beams, characterized in that, Includes the following steps: 1) Determine the basic parameters of the rusted reinforced concrete beam before CFRP reinforcement and the CFRP fabric, and determine the flexural bearing capacity of the rusted reinforced concrete beam before CFRP reinforcement and the target flexural bearing capacity of the rusted reinforced concrete beam after CFRP reinforcement according to actual needs. 2) Calculate the boundary parameters of the CFRP-reinforced corroded reinforced concrete beam based on the basic parameters in step 1); 3) Based on the results of step 2) and the flexural bearing capacity of the rusted reinforced concrete beam before CFRP reinforcement in step 1). ， Verify the limit bending capacity; 4) Based on the results of step 2), the limit flexural bearing capacity verified in step 3), and the target flexural bearing capacity of the CFRP-reinforced reinforced concrete beam after reinforcement in step 1), determine the flexural failure mode of the CFRP-reinforced reinforced concrete beam. 5) Determine the target bending failure mode based on actual needs. Based on the target bending failure mode and the target bending bearing capacity, and in combination with the limit bending bearing capacity verified in step 3) and the bending failure mode in step 4), design the required CFRP fabric reinforcement ratio. The basic parameters of the CFRP fabric used to reinforce the rusted reinforced concrete beam and the CFRP fabric include the cross-sectional width. b Cross-sectional height h Effective height of cross section h 0. Concrete strength grade, concrete compressive strength f c Concrete tensile strength f t , elastic modulus of concrete E c Types of deformed or plain reinforcing bars, and average corrosion rate of tensile reinforcing bars. η s Initial reinforcement area of ​​tensile reinforcement A s0 Elastic modulus of uncorroded steel bars E s0 Yield strength f y0 Ultimate strength f u0 Yield strain ε y0 Strengthening Response ε sh0 Ultimate strain ε u0 Ultimate tensile strain of CFRP fabric ε fu Elastic modulus E f Initial bending moment during reinforcement M i and tensile edge strain of concrete ε i ; The boundary parameters for CFRP-reinforced corroded reinforced concrete beams include boundary I (reinforcement ratio). ρ fsyb Boundary II reinforcement ratio ρ fshb Limit III reinforcement ratio ρ fsub Boundary IV reinforcement rate ρ fu Boundary I relative pressure zone height ξ fsyb Boundary II relative pressure zone height ξ fshb Boundary III relative pressure zone height ξ fsub Boundary IV relative pressure zone height ξ fu Boundary I flexural bearing capacity M uf,syb Bending capacity of limit II M uf,shb Bending capacity of limit III M uf,sub and Boundary IV flexural bearing capacity M uf,CFRP ; Boundary I indicates that when the beam fails under bending conditions, the corroded steel reinforcement just begins to yield, the concrete in the compression zone crushes, and the CFRP fabric does not break; boundary II indicates that when the beam fails under bending conditions, the corroded steel reinforcement just begins to strengthen, the concrete in the compression zone crushes, and the CFRP fabric does not break; boundary III indicates that when the beam fails under bending conditions, the fracture of the corroded steel reinforcement and the crushing of the concrete in the compression zone occur simultaneously, and the CFRP fabric does not break; boundary IV indicates that when the beam fails under bending conditions, the fracture of the CFRP fabric and the crushing of the concrete in the compression zone occur simultaneously. Calculate the reinforcement ratio of limit I ρ fsyb Boundary I relative pressure zone height ξ fsyb Boundary I flexural bearing capacity M uf,syb The specific steps include: a1) Induce strain in the corroded steel bars ε sc =ε yc ( η s ), stress of corroded steel bars σ sc =f yc ( η s ), the edge strain of the concrete in the compression zone ε c t = ε cu ,in ε yc ( η s )and f yc ( η s The values ​​represent the yield strain and yield stress of the corroded steel bars. ε cu The ultimate compressive strain of the concrete is equal to the strain of the corroded steel reinforcement. ε sc and the edge strain of the concrete in the compression zone ε c t Substituting into the deformation compatibility equation, solve for the relative height of the compression zone at boundary I. ξ fsyb ; a2) Relative height of boundary I to the pressure zone ξ fsyb Substitute the deformation compatibility equations and solve for the strain of the CFRP fabric. ε f ; a3) The relative height of the pressure zone ξ fsyb Stress from corroded steel bars σ sc =f yc ( η s ) and CFRP fabric strain ε f Substituting into the force equilibrium equation, we obtain the limit I reinforcement ratio. ρ fsyb ; a4) If the calculated limit I reinforcement ratio ρ fsyb ≤0, take ρ fsyb =0, then the limit I flexural bearing capacity M uf,syb = M uc ; M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fsyb >0, relative pressure zone height ξ fsyb CFRP cloth strain ε f and the reinforcement ratio of limit I ρ fsyb Substituting into the moment equilibrium equation, the calculation yields M uf,syb ; Calculation limit II reinforcement ratio ρ fshb Boundary II relative pressure zone height ξ fshb and Bending capacity of limit II M uf,shb The specific steps include: b1) Induce strain in the corroded steel bars ε sc =ε shc ( η s ), stress of corroded steel bars σ sc =f yc ( η s ), concrete strain at the edge of the compression zone ε c t = ε cu ,in ε shc ( η s The strain is the reinforcing strain for rusted steel bars. f yc ( η s The yield stress of the corroded steel bar is 1. ε cu The ultimate compressive strain of the concrete is equal to the strain of the corroded steel reinforcement. ε sc and the edge strain of the concrete in the compression zone ε c t Substituting into the deformation compatibility equation, we can solve for the relative compression zone height of boundary II. ξ fshb ; b2) The relative height of boundary II to the pressure zone ξ fshb Substitute the deformation compatibility equations and solve for the strain of the CFRP fabric. ε f ; b3) The relative height of the pressure zone ξ fshb Stress from corroded steel bars σ sc =f yc ( η s ) and CFRP fabric strain ε f Substituting into the force equilibrium equation, we obtain the reinforcement ratio of limit II. ρ fshb ; b4) If the calculated boundary II reinforcement ratio ρ fshb ≤0, take ρ fshb =0, then the flexural bearing capacity of limit II M uf,shb = M uc ; M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fshb >0, relative pressure zone height ξ fshb CFRP cloth strain ε f and the reinforcement ratio of boundary II ρ fshb Substituting into the moment equilibrium equation, the calculation yields M uf,shb ; Calculate the reinforcement ratio of limit III ρ fsub Boundary III relative pressure zone height ξ fsub and Bending capacity of limit III M uf,sub The specific steps include: c1) Cause the rusted steel bar to strain ε sc =ε suc ( η s ), stress of corroded steel bars σ sc =f uc ( η s ), concrete strain at the edge of the compression zone ε c t = ε cu ,in ε suc ( η s )and f uc ( η s The ultimate strain and ultimate stress of the corroded steel bars are given by the following parameters: ε cu The ultimate compressive strain of the concrete is equal to the strain of the corroded steel reinforcement. ε sc and the edge strain of the concrete in the compression zone ε c t Substituting into the deformation compatibility equation, solve for the relative compression zone height at boundary III. ξ fsub ; c2) The height of boundary III relative to the pressure zone ξ fsub Substitute the deformation compatibility equations and solve for the strain of the CFRP fabric. ε f ; c3) The relative height of the pressure zone ξ fsub Stress from corroded steel bars σ sc =f uc ( η s ) and CFRP fabric strain ε f Substituting into the force equilibrium equation, we obtain the reinforcement ratio for limit III. ρ fsub ; c4) If the calculated boundary III reinforcement ratio ρ fsub ≤0, take ρ fsub =0, then the flexural bearing capacity of limit III M uf,sub = M uc ; M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fsub >0, relative pressure zone height ξ fsub CFRP cloth strain ε f and the reinforcement ratio of boundary III ρ fsub Substituting into the moment equilibrium equation, the calculation yields M uf,sub ; Calculate the limit IV reinforcement ratio ρ fu Boundary IV relative pressure zone height ξ fu and the limit IV flexural bearing capacity M uf,CFRP The specific steps include: 1) Stress the CFRP fabric ε f =ε fu , Concrete strain at the edge of the compression zone ε c t = ε cu ,in ε fu For the ultimate tensile strain of CFRP fabric, ε cu Given the ultimate compressive strain of concrete, determine the strain of the corroded steel bars based on the deformation compatibility equation and the stress-strain relationship of the corroded steel bars. ε sc and stress of corroded steel bars σ sc CFRP cloth strain ε fu and the edge strain of the concrete in the compression zone ε cu Substituting into the deformation compatibility equation, solve for the relative compression zone height of boundary IV. ξ fu ; 2) Strain the CFRP fabric ε fu Stress from corroded steel bars σ sc Relative pressure zone height ξ fu Substituting into the force equilibrium equation, we obtain the reinforcement ratio at boundary IV. ρ fu ; 3) If the calculated limit IV reinforcement ratio ρ fu ≤0, take ρ fu =0, then the limit IV flexural bearing capacity M uf,CFRP = M uc ; M uc The flexural bearing capacity of the corroded reinforced concrete beam; if ρ fu >0, relative pressure zone height ξ fu CFRP cloth strain ε f and the limit IV reinforcement rate ρ fu Substituting into the moment equilibrium equation, the calculation yields M uf,CFRP .

2. The flexural design method for CFRP-reinforced corroded reinforced concrete beams according to claim 1, characterized in that, In step 4), based on the results of step 2) and the target flexural bearing capacity of the CFRP-reinforced corroded reinforced concrete beam in step 1), the flexural failure modes of the CFRP-reinforced corroded reinforced concrete beam include five types: like M uf ≤ M uf,CFRP If so, it is determined to be pattern ⑤; like M uf > M uf,CFRP and M uf > M uf,syb If so, it is determined to be pattern ①; like M uf > M uf,CFRP and M uf,syb ≥ M uf > M uf,shb If so, it is determined to be pattern ②; like M uf > M uf,CFRP and M uf,shb ≥ M uf > M uf,sub If so, it is determined to be pattern ③; like M uf > M uf,CFRP and M uf,sub ≥ M uf > M uc If so, it is determined to be pattern ④.

3. The flexural design method for CFRP-reinforced corroded reinforced concrete beams according to claim 2, characterized in that, Mode ⑤ represents the CFRP fabric failure under bending failure, with undetermined stress in the corroded steel reinforcement and the concrete in the compression zone; Mode ① represents the CFRP fabric failure without breakage under bending failure, with the corroded steel reinforcement exhibiting elasticity and the concrete in the compression zone undergoing crushing; Mode ② represents the CFRP fabric failure without breakage under bending failure, with the corroded steel reinforcement yielding and the concrete in the compression zone undergoing crushing; Mode ③ represents the CFRP fabric failure without breakage under bending failure, with the corroded steel reinforcement strengthening and the concrete in the compression zone undergoing crushing; Mode ④ represents the CFRP fabric failure without breakage under bending failure, with the corroded steel reinforcement breaking and the concrete in the compression zone undergoing crushing.

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