A method for calculating the flexural bearing capacity of CFRP cloth reinforced corroded reinforced concrete beams

Abstract

The present application relates to a kind of CFRP cloth reinforced corrosion reinforced concrete beam flexural capacity calculation method, comprising the following steps: 1) determine the basic parameters of corrosion reinforced concrete beam and CFRP cloth before CFRP cloth reinforcement;2) limit parameter is calculated based on the basic parameters of corrosion reinforced concrete beam of CFRP cloth reinforcement in step 1);3) the failure mode of corrosion reinforced concrete beam of CFRP cloth reinforcement is pre-judged based on the result of step 2);4) calculate the flexural capacity of corrosion reinforced concrete beam of CFRP cloth reinforcement and relative compression zone height under the pre-judged failure mode;5) according to the result of step 3), step 4) review failure mode and approve the flexural capacity of corrosion reinforced concrete beam of CFRP cloth reinforcement.Compared with prior art, the present application has the advantages of simple calculation, strong practicability, can predict flexural failure mode and corresponding failure mode CFRP stress state, steel stress state and concrete stress state etc..

Description

TECHNICAL FIELD

[0001] The present application relates to the civil engineering technical field, and particularly to a CFRP cloth reinforced corrosion reinforced concrete beam flexural capacity calculation method. BACKGROUND

[0002] During the service life of reinforced concrete beams, the decline of beam flexural performance caused by steel corrosion is a common problem. Steel corrosion can cause mechanical property degradation and effective cross-sectional area reduction, and the safety performance of corroded reinforced concrete beams is under test. Carbon fiber reinforced polymer (CFRP) has been widely used in the reinforcement of concrete structures, and the effectiveness of CFRP cloth in improving the flexural capacity of corroded reinforced concrete beams has been proven. Compared with non-corrosion reinforced concrete beams, CFRP cloth reinforcement makes the failure mode of corroded reinforced concrete beams more diverse, and the calculation of bearing capacity is more complex.

[0003] A large number of scholars at home and abroad have studied CFRP cloth reinforced non-corrosion concrete beams and proposed calculation methods based on the flexural capacity of the normal section. Considering the influence of corrosion, the flexural failure mode of CFRP cloth reinforced corroded reinforced concrete beams is quite different from that of non-corrosion reinforced beams. The research on CFRP cloth reinforced non-corrosion reinforced concrete beams is relatively mature, but the research on the flexural capacity of CFRP cloth reinforced corroded reinforced concrete beams is still to be further carried out. The existing calculation formula of the flexural capacity of CFRP cloth reinforced corroded reinforced concrete beams can be divided into two categories: I) the calculation formula obtained by modifying the flexural capacity of CFRP cloth reinforced non-corrosion beams based on the function of corrosion rate, CFRP reinforcement rate and other related parameters; II) the calculation formula of the flexural capacity of CFRP cloth reinforced corroded reinforced concrete beams obtained by considering the constitutive relationship of corroded steel, the degradation of the bonding performance between corroded steel and concrete, and other factors.

[0004] However, as the corrosion rate increases, the mechanical properties of steel change. At the same time, the CFRP cloth reinforcement amount may affect the stress state of the material at the flexural limit. The stress state of steel, CFRP and concrete of CFRP cloth reinforced corroded reinforced concrete beams at the flexural limit state is relatively complex. However, there is still a lack of a simplified calculation method for the flexural capacity of CFRP cloth reinforced corroded reinforced concrete beams based on the limit corrosion rate to clearly distinguish different flexural failure modes. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art and provide a CFRP cloth reinforced corrosion reinforced concrete beam flexural capacity calculation method.

[0006] The object of the present application can be achieved by the following technical solutions

[0007] A method for calculating the flexural bearing capacity of a CFRP cloth reinforced corroded reinforced concrete beam, comprising the following steps:

[0008] Step one, determine the basic parameters of the corroded reinforced concrete beam before and after CFRP cloth reinforcement.

[0009] The basic parameters of the CFRP cloth reinforced corroded reinforced concrete beam include; cross-sectional width b, cross-sectional height h, cross-sectional effective height h0, concrete strength grade, concrete compressive strength f c , concrete tensile strength f t , concrete elastic modulus E c , initial bending moment M i , tensile edge concrete strain under initial bending moment ε i ; the type of deformed or smooth round tensile and compressive reinforcement, the average corrosion rate of tensile reinforcement η s , the initial reinforcement area of tensile reinforcement A s0 ; the elastic modulus of non-corrosion tensile reinforcement E s0 , yield strength f y0 , ultimate strength f u0 , yield strain ε y0 , strengthening strain ε sh0 , ultimate strain ε u0 ; the ultimate tensile strain of CFRP cloth ε fu , CFRP cloth reinforcement rate ρ f , CFRP cloth elastic modulus E f .

[0010] In this step, the cross-sectional width b, the cross-sectional height h, the cross-sectional effective height h0, the concrete strength grade, the concrete compressive strength f c , the concrete tensile strength f t , the concrete elastic modulus E c , the type of deformed or smooth round tensile and compressive reinforcement, the average corrosion rate of tensile reinforcement η s , the initial reinforcement area of tensile reinforcement A s0 , the elastic modulus of non-corrosion tensile reinforcement E s0 , yield strength f y0 , ultimate strength f u0 , yield strain ε y0 , strengthening strain ε sh0 , ultimate strain ε u0The parameters can be measured according to the method described in the Standard for Field Testing Techniques of Concrete Structures GB / T 50784-2013; if the mechanical property parameters of the non-corroded steel bars are not convenient to obtain, the values can be taken according to the Code for Design of Concrete Structures GB50010-2010 (2015 Edition); the reinforcement rate p of the CFRP f Determined according to the actual situation; the elastic modulus E of the CFRP f Determined according to the Standard for Engineering Application Technology of Fiber Reinforced Composites GB50608-2020; the initial bending moment M i Estimated according to the actual situation; the strain e of the tensile edge concrete under the initial bending moment i Determined according to the Standard for Engineering Application Technology of Fiber Reinforced Composites GB50608-2020; the flexural capacity M of the corroded reinforced concrete beam uc Obtained through relevant calculation methods, for example, the Simplified Calculation Method for Flexural Capacity of Corroded Reinforced Concrete Beams (Patent Application No. CN202011502706.X).

[0011] Step two, calculate the limit parameters of the CFRP cloth reinforced corroded reinforced concrete beam.

[0012] The limit parameters of the CFRP cloth reinforced corroded reinforced concrete beam include: limit I corrosion rate η f syb , limit II corrosion rate η f shb , limit III corrosion rate η f sub ; limit I relative compressive zone height ξ fsyb , limit II relative compressive zone height ξ fshb , limit III relative compressive zone height ξ fsub , and limit IV relative compressive zone height ξ fu .

[0013] Limit I is defined as: the corroded steel bars begin to yield when the beam is flexurally damaged, the compressive zone concrete is crushed, and the CFRP cloth is not broken; limit II is defined as: the corroded steel bars begin to strengthen when the beam is flexurally damaged, the compressive zone concrete is crushed, and the CFRP cloth is not broken; limit III is defined as: the corroded steel bars are broken and the compressive zone concrete is crushed at the same time when the beam is flexurally damaged, and the CFRP cloth is not broken; limit IV is defined as: the CFRP cloth is broken and the compressive zone concrete is crushed at the same time when the beam is flexurally damaged.

[0014] In this step, the corrosion rate η f syb of limit I and the relative compressive zone height ξ fsyb of limit I are calculated as follows:

[0015] 1) Take the strain of the corroded steel bar ε sc = ε yc (η s ), the stress of the corroded steel bar σ sc = f yc (η s ), the strain of the concrete at the edge of the compression zone ε c t = ε cu , where ε yc (η s ) and f yc (η s ) are the yield strain and the yield stress of the corroded steel bar respectively, and ε cu is the ultimate compressive strain of the concrete, calculate the relative compression zone height ξ fsyb of the limit I according to the deformation compatibility equation;

[0016] 2) Calculate the tensile strain of the CFRP ε f according to the deformation compatibility equation;

[0017] 3) Substitute the strain of the corroded steel bar ε sc , the stress of the corroded steel bar σ sc and the tensile strain of the CFRP ε f into the force balance equation to obtain a cubic equation of η s , solve the cubic equation, and take the minimum solution in the range of 0-0.8 as the limit corrosion rate η f syb of the limit I, if there is no solution in the range of 0-0.8 and the minimum solution is negative, take η f syb = 0, if there is no solution in the range of 0-0.8 and the minimum solution is greater than 0.8, take η f syb = 0.8.

[0018] In this step, the calculation steps of the limit corrosion rate η f shb of the limit II and the relative compression zone height ξ fshb of the limit II are as follows:

[0019] 1) Take the strain of the corroded steel bar ε sc = ε shc (η s ), the stress of the corroded steel bar σ sc = f yc (η s ), the strain of the concrete at the edge of the compression zone ε c t = ε cu , where ε shc (η s ) and fyc (η s ) is the strain and yield stress of corroded reinforcement, respectively, ε cu is the ultimate compressive strain of concrete, according to the deformation compatibility equation, the relative compressive zone height ξ fshb of limit II is solved;

[0020] 2) According to the deformation compatibility equation, the CFRP tensile strain ε f is obtained;

[0021] 3) The corroded reinforcement strain ε sc , the corroded reinforcement stress σ sc and the CFRP tensile strain ε f are substituted into the force balance equation, and according to the stress-strain relationship of the corroded reinforcement and the force balance equation, a quartic equation about η s is obtained, and by taking (1-1.092η s ) / (1-η s )=1 to simplify, a quadratic equation is obtained, and the original equation or the simplified equation is solved, and the smaller solution of η f syb <η s <η s,cr in the above range is taken as the limit II corrosion rate η f shb , and if there is no solution in the above range, η f shb =η f syb .

[0022] In this step, the calculation steps of the limit III corrosion rate η f sub and the relative compressive zone height ξ fsub are as follows:

[0023] 1) Take the corroded reinforcement strain ε sc =ε suc (η s ), the corroded reinforcement stress σ sc =f uc (η s ), and the section compressive zone edge concrete strain ε c t =ε cu , wherein ε suc (η s ) and f uc (η s ) are the ultimate strain and ultimate stress of the corroded reinforcement, respectively, and ε cu is the ultimate compressive strain of concrete; according to the deformation compatibility equation, the relative compressive zone height ξ fsub of limit III is solved;

[0024] 2) Based on the deformation compatibility equation, the CFRP brala strain ε is obtained. f ;

[0025] 3) The strain ε of the corroded steel bar sc σ stress of corroded steel bars sc With CFRP Bragg strain ε f Substituting into the force balance equation, we can obtain information about η. s A quadratic equation in one variable, taking η f shb <η s The smaller solution within the range <0.8 is used as the boundary III corrosion rate η. f sub If the equation has no solution within the above range, take η. f sub =0.8.

[0026] In this step, the relative pressure zone height ξ of boundary IV fu The calculation steps are as follows:

[0027] Let CFRP be strained ε f =ε fu ε, the concrete strain at the edge of the compression zone of the cross section c t =ε cu , where ε fu For the ultimate tensile strain of CFRP fabric, ε cu Substituting the ultimate compressive strain of the concrete into the deformation compatibility equation, we can solve for the relative height ξ of the compression zone at the limit IV. fu .

[0028] Step 3: Predict the failure mode of CFRP-reinforced corroded reinforced concrete beams.

[0029] The failure modes of CFRP-reinforced corroded reinforced concrete beams include:

[0030] 1) When 0 ≤ η s <η f syb If the condition is as described above, it is determined to be mode ①, that is, when the CFRP fabric is not broken during bending failure, the corroded steel bar is elastic, and the concrete in the compression zone is crushed.

[0031] 2) When η f syb ≤η s <η f shb If the condition is as described above, it is determined to be mode ②, that is, when the CFRP fabric fails under bending, the corroded steel bars yield, and the concrete in the compression zone is crushed.

[0032] 3) When η fshb ≤η s <η f sub then, it is determined as mode ③, i.e. the CFRP sheet is not pulled off, the corroded steel bars are strengthened, and the concrete in the compression zone is crushed when bending failure occurs;

[0033] 4) when η f sub ≤η s <1, it is determined as mode ④, i.e. the CFRP sheet is not pulled off, the corroded steel bars are pulled off, and the concrete in the compression zone is crushed when bending failure occurs.

[0034] Step four, calculating the flexural capacity of the CFRP sheet reinforced corroded steel reinforced concrete beam and the relative compression zone height under the pre-judgment failure mode.

[0035] The flexural capacity and the relative compression zone height include: the flexural capacity M u and the relative compression zone height ξ of mode ①, the flexural capacity M u and the relative compression zone height ξ of mode ②, the flexural capacity M u and the relative compression zone height ξ of mode ③, and the flexural capacity M u and the relative compression zone height ξ of mode ④.

[0036] Among them, the flexural capacity M u and the relative compression zone height ξ corresponding to mode ①, the calculation steps are as follows:

[0037] 1) Let the strain of the edge concrete in the compression zone of the section ε c t = ε cu , wherein ε cu is the ultimate compressive strain of the concrete, and the strain ε sc (ξ) of the corroded steel bar and the tensile strain ε f (ξ) of the CFRP sheet related to the relative compression zone height ξ can be obtained according to the strain compatibility relationship;

[0038] 2) Substitute the strain ε sc (ξ) of the corroded steel bar into the stress-strain relationship of the corroded steel bar to obtain the stress σ sc (ξ) of the corroded steel bar, and substitute the stress σ sc (ξ) of the corroded steel bar and the tensile strain ε f (ξ) of the CFRP sheet into the force balance equation to obtain a quadratic equation about the relative compression zone height ξ. Solve the equation, and take the larger solution in the range of ξ>ξ fsyb as the value of the relative compression zone height ξ of mode ①;

[0039] 3) Substitute the relative compression zone height ξ and the tensile strain ε f(ξ) into the bending moment equilibrium equation to solve the flexural capacity M u .

[0040] the flexural capacity M u and the relative compression zone height ξ, the calculation steps are as follows:

[0041] 1) Let the concrete strain ε c t = ε cu , where ε cu is the ultimate compressive strain of concrete, and substitute it into the deformation compatibility equation to obtain the corrosion steel strain ε sc (ξ) and the CFRP tensile strain ε f (ξ) related to the relative compression zone height ξ;

[0042] 2) Let the corrosion steel stress σ sc = f yc (η s ), where f yc (η s ) is the yield stress of corrosion steel, and substitute the corrosion steel stress σ sc and the CFRP tensile strain ε f (ξ) into the force equilibrium equation to obtain a quadratic equation about the relative compression zone height ξ, solve the equation, and take the larger solution in the range of ξ fsyb ≥ ξ > ξ fshb as the relative compression zone height ξ of mode 2;

[0043] 3) Substitute the relative compression zone height ξ and the CFRP tensile strain ε f (ξ) into the bending moment equilibrium equation to solve the flexural capacity M u .

[0044] the flexural capacity M u and the relative compression zone height ξ, the calculation steps are as follows:

[0045] 1) Let the concrete strain ε c t = ε cu , where ε cu is the ultimate compressive strain of concrete, and according to the strain compatibility relationship, the corrosion steel strain ε sc (ξ) and the CFRP tensile strain ε f (ξ) related to the relative compression zone height ξ can be obtained;

[0046] 2) Substitute the corrosion steel strain ε sc (ξ) into the stress-strain relationship of corrosion steel to obtain the corrosion steel stress σ sc(ξ), the stress σ sc (ξ) and the CFRP tensile strain ε f (ξ) into the force equilibrium equation, a quadratic equation about the relative compression zone height ξ is obtained, and the solution of the equation is taken as the value of the relative compression zone height ξ fshb ≥ξ>ξ fsub The larger solution in the range is taken as the value of the relative compression zone height ξ of mode ③;

[0047] 3) The relative compression zone height ξ and the CFRP tensile strain ε f (ξ) are substituted into the moment equilibrium equation to solve the flexural capacity M u of mode ③.

[0048] Mode ④ is divided into two subcategories: A) the CFRP is in an elastic state and the concrete is not crushed when the steel bar is pulled apart, and the flexural capacity of the CFRP reinforced corroded reinforced concrete beam is M u1 ; B) the CFRP is elastic and the concrete is crushed after the steel bar is pulled apart, and the corresponding flexural capacity is M u2 ; the flexural capacity M u of the CFRP reinforced corroded reinforced concrete beam corresponding to mode ④ is taken as the maximum value of M u1 and M u2 , and the specific calculation steps are as follows:

[0049] 1) Take the relative compression zone height ξ = ξ fsub , the steel bar strain ε sc = ε suc (η s ), wherein ξ fsub is the relative compression zone height corresponding to the limit corrosion rate III, and ε suc (η s ) is the ultimate strain of the corroded steel bar, and the deformation compatibility equation is substituted to obtain the CFRP tensile strain value ε f (ξ) related to the relative compression zone height;

[0050] 2) Take the steel bar stress σ sc = f uc (η s ), wherein f uc (η s ) is the ultimate stress of the corroded steel bar, and the moment of the corroded steel bar tension and the CFRP tension on the concrete compression force point is solved to obtain the flexural capacity M u1 of the CFRP reinforced corroded reinforced concrete beam in the A category, and the calculation formula is as follows:

[0051]

[0052] 3) Let the concrete strain ε ct = ε cu , where ε cu is the ultimate compressive strain of concrete, substitute into the deformation compatibility equation to obtain CFRP strain ε f (ξ), take the stress of corroded steel bar σ sc = 0, calculate the relative compressive zone height ξ, and substitute the relative compressive zone height ξ into the moment equilibrium equation to solve the flexural capacity M u2 of CFRP sheet reinforced corroded reinforced concrete beam in case B.

[0053] Step five, review the failure mode and determine the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beam.

[0054] The failure mode review and capacity determination include:

[0055] 1) ξ ≥ ξ fu , the failure mode determined in step three is true, and the capacity calculated in step four is true;

[0056] 2) ξ < ξ fu , the true failure mode is mode ⑤, and the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beam in mode ⑤ is calculated.

[0057] Further, the failure mode ⑤ in step five is divided into two subcategories: A) CFRP is pulled off, and the concrete is not crushed, at this time the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beam is M u1 ; B) CFRP is pulled off, and CFRP sheet reinforced corroded reinforced concrete beam degenerates into an unsupplemented corroded reinforced concrete beam, and the corresponding flexural capacity is M uc ; the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beam M u is taken as the larger value of M u1 and M uc , and the calculation steps are as follows:

[0058] 1) take the relative compressive zone height ξ = ξ fu , the CFRP tensile strain ε f = ε fu , where ξ fu is the relative compressive zone height of limit IV, ε fu is the ultimate tensile strain of CFRP, substitute into the deformation compatibility equation and the stress-strain relationship of corroded steel bar to obtain the stress of corroded steel bar σ sc (ξ) related to the relative compressive zone height, and M u1 is calculated by the following formula;

[0059]

[0060] 2) M ucThe flexural bearing capacity of the corresponding corroded reinforced concrete beam is determined by a corresponding calculation method.

[0061] Further, in the above steps two to five, the force balance equation calculation formula is:

[0062] α1f c bξh=E f ε f A f +σ sc A s0 (1-η s )

[0063] Wherein, α1 is the equivalent rectangular coefficient, when the concrete strength grade is less than or equal to C50, α1 = 1.0;

[0064] The calculation formula of the bending moment balance equation of the CFRP cloth reinforced corroded reinforced concrete beam is:

[0065] M uf =α1f c bξh(h0-0.5ξh)+E f ε f A f (h-h0)

[0066] =α1f c bξh(h0-0.5ξh)+[α1f c bξh-σ sc A s0 (1-η s )](h-h0)

[0067] The calculation formula of the deformation compatibility equation is:

[0068]

[0069] Wherein, β1 is the equivalent rectangular coefficient, when the concrete strength grade is less than or equal to C50, β1 = 0.8; x n is the actual strain distribution height, ε c t is the compressive strain of the top of the concrete, ε f is the CFRP tensile strain.

[0070] The calculation formula of the stress-strain relationship of the corroded steel bar is:

[0071]

[0072] The calculation formula of the elastic modulus of the corroded steel bar is:

[0073] E sc =E s0

[0074] The formula for calculating the yield stress of the corroded steel bar is:

[0075]

[0076] The formula for calculating the ultimate stress of the corroded steel bar is:

[0077]

[0078] The formula for calculating the yield strain of the corroded steel bar is:

[0079]

[0080] The formula for calculating the strengthening strain of the corroded steel bar is:

[0081]

[0082] The formula for calculating the ultimate strain of the corroded steel bar is:

[0083]

[0084] The formula for calculating the strengthening modulus of the corroded steel bar is:

[0085]

[0086] The method for calculating the flexural bearing capacity of the CFRP cloth reinforced corroded reinforced concrete beam provided by the present application at least includes the following beneficial effects compared with the prior art:

[0087] The present application considers the influence of the steel bar corrosion rate, and can calculate three kinds of limit corrosion rates and four kinds of damage limits through section analysis. Based on this, five kinds of damage modes of the CFRP cloth reinforced corroded reinforced concrete beam can be distinguished, and the flexural failure mode and the corresponding damage mode of the CFRP stress state, the steel bar stress state and the concrete stress state can be predicted. Finally, the calculation mode and the flexural bearing capacity of the CFRP cloth reinforced corroded reinforced concrete beam are determined through review, the method is clear in concept, easy to calculate and has good practicability. BRIEF DESCRIPTION OF DRAWINGS

[0088] Fig. 1 The figure (a) is a stress distribution diagram of the CFRP cloth reinforced corroded reinforced concrete beam, and the figure (b) is an equivalent stress distribution diagram of the CFRP cloth reinforced corroded reinforced concrete beam. The figure (c) is a strain distribution diagram of the CFRP cloth reinforced corroded reinforced concrete beam.

[0089] Fig. 2 The example illustrates the CFRP fabric-reinforced rusted reinforced concrete beam flexural bearing capacity calculation method, including the CFRP fabric-reinforced rusted reinforced concrete beam CFRP elastic failure mode and strain distribution.

[0090] Fig. 3 This example illustrates the failure mode and strain distribution of a CFRP-reinforced reinforced concrete beam at CFRP tensile fracture, which is involved in the calculation method for the flexural bearing capacity of the CFRP-reinforced corroded reinforced concrete beam. Detailed Implementation

[0091] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0092] Example

[0093] This invention relates to a method for calculating the flexural bearing capacity of CFRP-reinforced corroded reinforced concrete beams. This method can conveniently and accurately predict the failure mode and calculate the flexural bearing capacity of CFRP-reinforced corroded reinforced concrete beams under different failure modes.

[0094] Combination Figs. 1-3 As shown, the method for calculating the flexural bearing capacity of CFRP-reinforced corroded reinforced concrete beams according to the present invention includes the following steps:

[0095] S1: Determine the basic parameters of the corroded reinforced concrete beam before and after CFRP reinforcement.

[0096] The basic parameters for CFRP-reinforced corroded reinforced concrete beams include: section width b, section height h, effective section height h0, concrete strength grade, and concrete compressive strength f. c Concrete tensile strength f t E, the elastic modulus of concrete c Initial bending moment M i ε of the tensile edge concrete under initial bending moment i The types of deformed or plain round tensile and compressive reinforcing bars, and the average corrosion rate η of tensile reinforcing bars. s Initial reinforcement area A of tensile reinforcement s0 ; 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 ; Ultimate tensile strain ε of CFRP clothfu CFRP fabric reinforcement ratio ρ f CFRP fabric elastic modulus E f .

[0097] In this step, the cross-sectional width b, cross-sectional height h, effective cross-sectional height h0, concrete strength grade, and concrete compressive strength f are specified. c Concrete tensile strength f t E, the elastic modulus of concrete c Types of deformed or plain round tensile and compressive reinforcing bars; average corrosion rate η of tensile reinforcing 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 Parameters such as these can be measured according to the methods described in GB / T 50784-2013, "Technical Standard for On-site Testing of Concrete Structures"; if the mechanical performance parameters of uncorroded reinforcing bars are inconvenient to obtain, they can be taken from GB50010-2010 (2015 edition), "Code for Design of Concrete Structures"; the reinforcement ratio ρ of CFRP... f Determined based on actual conditions; CFRP elastic modulus E f The ultimate tensile strain of CFRP can be determined according to the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" GB50608-2020; the initial bending moment M i Estimate the strain ε of the tensile edge concrete under the initial bending moment based on the actual situation. i The flexural bearing capacity M of the corroded reinforced concrete beam is determined according to the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" GB50608-2020. uc It can be obtained through relevant calculation methods, such as a simplified calculation method for the flexural bearing capacity of the normal section of a corroded reinforced concrete beam (patent application number: CN202011502706.X).

[0098] S2: Calculate the limit parameters for CFRP-reinforced corroded reinforced concrete beams.

[0099] The limiting parameters for CFRP-reinforced corroded reinforced concrete beams include: Limiting corrosion rate η. f syb , Boundary II corrosion rate η f shb η, the corrosion rate of boundary III f sub ; Boundary I relative to the height of the pressure zone ξ fsyb Boundary II relative pressure zone height ξfshb , the relative compression zone height ξ of limit III fsub , and the relative compression zone height ξ of limit IV fu .

[0100] In this step, the corrosion rate η of limit I f syb , and the relative compression zone height ξ of limit I fsyb are calculated as follows:

[0101] 1) Take the corrosion steel bar strain ε sc = ε yc (η s ), the corrosion steel bar stress σ sc = f yc (η s ), the section compression zone edge concrete strain ε c t = ε cu , where ε yc (η s ) and f yc (η s ) are the yield strain and yield stress of the corrosion steel bar respectively, and ε cu is the ultimate compression strain of the concrete, according to the deformation compatibility equation, the relative compression zone height ξ of limit I fsyb is calculated;

[0102] 2) According to the deformation compatibility equation, the CFRP cloth tensile strain ε f is calculated;

[0103] 3) Substitute the corrosion steel bar strain ε sc , the corrosion steel bar stress σ sc , and the CFRP cloth tensile strain ε f into the force balance equation to obtain a cubic equation about η s , solve the cubic equation, and take the minimum solution in the range of 0-0.8 as the limit corrosion rate η f syb of limit I. If there is no solution in the range of 0-0.8 and the minimum solution is negative, take η f syb = 0, if there is no solution in the range of 0-0.8 and the minimum solution is greater than 0.8, take η f syb = 0.8.

[0104] In this step, the corrosion rate η of limit II f shb , and the relative compression zone height ξ of limit II fshb are calculated as follows:

[0105] 1) Take the corrosion steel bar strain ε sc= ε shc (η s ) and f sc (η yc ) are the strain and yield stress of corroded reinforcement, respectively, and ε s is the ultimate compressive strain of concrete, the relative compressive zone height ξ c of limit II is solved according to the deformation compatibility equation. t = ε cu , where ε shc (η s ) and f yc (η s ) are the strain and yield stress of corroded reinforcement, respectively, and ε cu is the ultimate compressive strain of concrete, the relative compressive zone height ξ fshb of limit II is solved according to the deformation compatibility equation.

[0106] 2) The CFRP tensile strain ε f is obtained according to the deformation compatibility equation.

[0107] 3) The corroded reinforcement strain ε sc , the corroded reinforcement stress σ sc and the CFRP tensile strain ε f are substituted into the force equilibrium equation, and a monomial quartic equation about η s is obtained according to the strain-stress relationship of corroded reinforcement and the force equilibrium equation, and a monomial quadratic equation is obtained by taking (1-1.092η s ) / (1-η s )=1 to simplify, and the original equation or the simplified equation is solved, and the smaller solution of η f syb < η s < η s,cr in the range is taken as the limit II corrosion rate η f shb , and if there is no solution in the above range, η f shb = η f syb .

[0108] In this step, the calculation steps of the limit III corrosion rate η f sub and the relative compressive zone height ξ fsub are as follows:

[0109] 1) Take the corroded reinforcement strain ε sc = ε suc (η s ), the corroded reinforcement stress σ sc = f uc (η s ), and the section compressive zone edge concrete strain ε ct = ε cu , where ε suc = ε s and f uc (η s ) are the ultimate strain and stress of the corroded steel bar, respectively, and ε cu is the ultimate compressive strain of the concrete; according to the deformation compatibility equation, the relative compressive zone height ξ fsub of limit III is solved;

[0110] 2) According to the deformation compatibility equation, the CFRP tensile strain ε f is obtained;

[0111] 3) The corroded steel bar strain ε sc , the corroded steel bar stress σ sc , and the CFRP tensile strain ε f are substituted into the force balance equation, and a quadratic equation about η s is obtained, and the smaller solution of η f in the range of <η shb <0.8> is taken as the limit III corrosion rate η s f sub , and if there is no solution in the above range, η f sub =0.8 is taken.

[0112] In this step, the calculation steps of the relative compressive zone height ξ fu of limit IV are as follows:

[0113] Let the CFRP tensile strain ε f = ε fu , the compressive zone edge concrete strain ε c = ε t , and the compressive zone edge concrete strain ε cu = ε fu , where ε cu is the ultimate tensile strain of the CFRP, and ε fu is the ultimate compressive strain of the concrete; the deformation compatibility equation is substituted, and the relative compressive zone height ξ s of limit IV is solved.

[0114] S3: Pre-judge the failure mode of the CFRP reinforced corroded steel reinforced concrete beam.

[0115] The failure mode of the CFRP reinforced corroded steel reinforced concrete beam includes:

[0116] 1) When 0≤η f < η syb <0.8>, it is determined as mode ①, i.e., the CFRP is not broken, the corroded steel bar is elastic, and the compressive zone concrete is crushed when the flexural failure occurs;

[0117] 2) When η f syb ≤η s <η f shb If the condition is as described above, it is determined to be mode ②, that is, when the CFRP fabric fails under bending, the corroded steel bars yield, and the concrete in the compression zone is crushed.

[0118] 3) When η f shb ≤η s <η f sub If the condition is as described above, it is determined to be mode ③, that is, when the CFRP fabric fails under bending, the rusted steel reinforcement is strengthened, and the concrete in the compression zone is crushed.

[0119] 4) When η f sub ≤η s When the value is less than 1, 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.

[0120] S4: Calculate the flexural bearing capacity and relative compression zone height of CFRP-reinforced corroded reinforced concrete beams under the predicted failure mode.

[0121] Bending capacity and relative compression zone height include: Mode ① Bending capacity M u and relative compression zone height ξ, bending bearing capacity M of mode ② u and relative compression zone height ξ, bending bearing capacity M of mode ③ u and relative compression zone height ξ and mode ④ flexural bearing capacity M u And the relative height of the pressure zone, ξ.

[0122] Among them, the flexural bearing capacity M corresponding to mode ① u The calculation steps for the relative pressure zone height ξ are as follows:

[0123] 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 can be obtained based on the strain compatibility relationship and its relationship with the relative height of the compression zone ξ. sc (ξ) and CFRP Bragg strain ε f (ξ);

[0124] 4) 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 (ξ) and CFRP Bragg strain εf (ξ) into the force equilibrium equation, a quadratic equation about the relative compression zone height ξ is obtained. Solving the equation, the larger solution in the range of ξ > ξ fsyb is taken as the value of the relative compression zone height ξ of mode 1;

[0125] 5) Substitute the relative compression zone height ξ and the CFRP tensile strain ε f (ξ) into the moment equilibrium equation to solve the flexural capacity M u .

[0126] The flexural capacity M u and the relative compression zone height ξ of mode 2 are calculated as follows:

[0127] 1) Let the concrete strain ε c t = ε cu , where ε cu is the ultimate compressive strain of concrete, substitute the deformation compatibility equation, the corroded steel bar strain ε sc (ξ) and the CFRP tensile strain ε f (ξ) related to the relative compression zone height ξ are obtained;

[0128] 2) Let the corroded steel bar stress σ sc = f yc (η s ), where f yc (η s ) is the yield stress of the corroded steel bar, substitute the corroded steel bar stress σ sc and the CFRP tensile strain ε f (ξ) into the force equilibrium equation, a quadratic equation about the relative compression zone height ξ is obtained, solving the equation, the larger solution in the range of ξ fsyb ≥ ξ > ξ fshb is taken as the value of the relative compression zone height ξ of mode 2;

[0129] 3) Substitute the relative compression zone height ξ and the CFRP tensile strain ε f (ξ) into the moment equilibrium equation to solve the flexural capacity M u .

[0130] The flexural capacity M u and the relative compression zone height ξ of mode 3 are calculated as follows:

[0131] 1) Let the concrete strain ε c t = ε cu , where ε cuFor the ultimate compressive strain of concrete, the strain of corroded steel bar ε sc (ξ) related to the relative compressive zone height ξ can be obtained according to the strain compatibility relationship f (ξ);

[0132] 2) Substitute the strain of corroded steel bar ε sc (ξ) into the stress-strain relationship of corroded steel bar to obtain the stress σ sc (ξ) of corroded steel bar, and substitute the stress σ sc (ξ) of corroded steel bar and the tensile strain ε f (ξ) of CFRP into the force balance equation to obtain a quadratic equation about the relative compressive zone height ξ, solve the equation, and take the larger solution in the range of ξ fshb ≥ξ>ξ fsub as the value of the relative compressive zone height ξ of mode ③;

[0133] 3) Substitute the relative compressive zone height ξ and the tensile strain ε f (ξ) of CFRP into the bending moment balance equation to solve the bending capacity M u of mode ③.

[0134] Mode ④ is divided into two subcategories: A) when the steel bar is pulled off, the CFRP is in an elastic state, and the concrete is not crushed, at this time the bending capacity of the CFRP reinforced corroded steel reinforced concrete beam is M u1 ; B) after the steel bar is pulled off, the CFRP is elastic, and the concrete is crushed, the corresponding bending capacity is M u2 ; the bending capacity M u of the CFRP reinforced corroded steel reinforced concrete beam corresponding to mode ④ is taken as the larger value of M u1 and M u2 , and the specific calculation steps are as follows:

[0135] 1) Take the relative compressive zone height ξ = ξ fsub , the strain of corroded steel bar ε sc = ε suc (η s ), where ξ fsub is the relative compressive zone height corresponding to the limit corrosion rate III, and ε suc (η s ) is the ultimate strain of corroded steel bar, and substitute into the deformation compatibility equation to obtain the tensile strain value ε f (ξ) of CFRP related to the relative compressive zone height;

[0136] 2) Take the stress σ sc = f uc (η s ) of corroded steel bar, where f uc (η s)rusting steel ultimate stress, rusting steel tension and CFRP tension to solve the bending capacity of CFRP reinforced rusting steel reinforced concrete beam M u1 , the formula is as follows:

[0137]

[0138] 3) let the edge of the section compression zone concrete strain ε c t = ε cu , where ε cu is the ultimate compressive strain of concrete, substitute the deformation compatibility equation to obtain the CFRP strain ε f (ξ), take the rusting steel stress σ sc = 0, calculate the relative compression zone height ξ, and substitute the relative compression zone height ξ into the bending moment balance equation to solve the bending capacity of CFRP reinforced rusting steel reinforced concrete beam M u2 .

[0139] S5: review the failure mode and determine the bending capacity of CFRP reinforced rusting steel reinforced concrete beam.

[0140] The failure mode review and capacity determination includes:

[0141] 1) ξ ≥ ξ fu , the failure mode determined in S3 is true, and the capacity calculated in S4 is true;

[0142] 2) ξ < ξ fu , the true failure mode is mode ⑤, and the bending capacity of CFRP reinforced rusting steel reinforced concrete beam under mode ⑤ is calculated.

[0143] Further, the failure mode ⑤ in S5 is divided into two subcategories: A) CFRP is pulled off, and the concrete is not crushed, at this time the bending capacity of CFRP reinforced rusting steel reinforced concrete beam is M u1 ; B) CFRP is pulled off, and CFRP reinforced rusting steel reinforced concrete beam degenerates into non-reinforced rusting steel reinforced concrete beam, and the corresponding bending capacity is M uc ; the bending capacity of CFRP reinforced rusting steel reinforced concrete beam M u , take the larger value of M u1 and M uc , the calculation steps are as follows:

[0144] 1) take the relative compression zone height ξ = ξ fu , the CFRP tension strain ε f = ε fu , where ξ fu is the relative compression zone height of limit IV, and ε fuFor the ultimate tensile strain of CFRP, the deformation compatibility equation and the stress-strain relationship of the corroded steel bar are substituted to obtain the stress of the corroded steel bar σ sc (ξ), M u1 The calculation is performed by the following formula:

[0145]

[0146] 2)M uc The flexural capacity of the corresponding corroded reinforced concrete beam is determined.

[0147] Further, in the above S2, S3, S4, S5, the force balance equation calculation formula is:

[0148] α1f c bξh=E f ε f A f +σ sc A s0 (1-η s )

[0149] Wherein, α1 is the equivalent rectangular coefficient, when the concrete strength grade is less than or equal to C50, α1 = 1.0;

[0150] The flexural moment balance equation calculation formula of the CFRP reinforced corroded reinforced concrete beam is:

[0151] M uf =α1f c bξh(h0-0.5ξh)+E f ε f A f (h-h0)

[0152] =α1f c bξh(h0-0.5ξh)+[α1f c bξh-σ sc A s0 (1-η s )](h-h0)

[0153] The deformation compatibility equation calculation formula is:

[0154]

[0155] Wherein, β1 is the equivalent rectangular coefficient, when the concrete strength grade is less than or equal to C50, β1 = 0.8; x n is the actual strain distribution height, ε c t is the compressive strain of the top of the concrete, ε f is the CFRP tensile strain.

[0156] The stress-strain relationship calculation formula of the corroded steel bar is:

[0157]

[0158] The elastic modulus calculation formula of the corroded steel bar is:

[0159] E sc = E s0

[0160] The yield stress calculation formula of the corroded steel bar is:

[0161]

[0162] The ultimate stress calculation formula of the corroded steel bar is:

[0163]

[0164] The yield strain calculation formula of the corroded steel bar is:

[0165]

[0166] The strengthening strain calculation formula of the corroded steel bar is:

[0167]

[0168] The ultimate strain calculation formula of the corroded steel bar is:

[0169]

[0170] The strengthening modulus calculation formula of the corroded steel bar is:

[0171]

[0172] The above method of the present application is further illustrated by the actual implementation process in this embodiment.

[0173] In this embodiment, a certain laboratory in Shanghai obtained four CFRP cloth reinforced corrosion reinforced concrete beam specimens (Nos. L1, L2, L3 and L4) with different corrosion degrees by using the method of power-on accelerated corrosion.

[0174] (1) Determine the basic parameters of the corroded steel reinforced concrete beam before and after the CFRP cloth reinforcement

[0175] According to the method described in the "Standard for Field Testing Techniques of Concrete Structures" GB / T 50784-2013, the four CFRP reinforced corrosion reinforced concrete beams are measured to be rectangular in cross section, and the beam cross section width b, cross section height h, cross section effective height h0, measured concrete compressive strength f c , the tensile strength of concrete f t , as shown in Table 1; the average corrosion rate of the tensile reinforcement η s , the cross section reinforcement information (according to which the initial tensile reinforcement area A s0 , as shown in Table 1; the elastic modulus of the non-corrosion tensile reinforcement E s0 , the yield strength f y0 , the ultimate strength f u0 , the yield strain ε y0 , the strain ε sh0 , the ultimate strain ε u0 , as shown in Table 2; the mechanical properties of CFRP cloth are provided by the manufacturer, and the values are taken according to the "Standard for Engineering Application Technology of Fiber Reinforced Composite Materials (GB50608-2020)", the elastic modulus of CFRP E f , the allowable tensile strain of CFRP ε fu , the CFRP reinforcement rate is shown in Table 3. The initial bending moment M i = 0, the initial tensile strain of concrete ε i = 0, and the effect of secondary reinforcement is not considered.

[0176] Table 1 CFRP cloth reinforced corrosion reinforced concrete beam specimen related parameters

[0177]

[0178] Table 2 Initial mechanical properties of tensile reinforcement

[0179]

[0180] Table 3 CFRP mechanical properties

[0181]

[0182] (2) Calculate the limit parameters of CFRP cloth reinforced corrosion reinforced concrete beam.

[0183] Beam L1:

[0184] 21) Calculate the limit I corrosion rate η f syb and the limit I relative compression zone height ξ fsyb

[0185] The yield stress and yield strain of the corrosion reinforcement are:

[0186]

[0187]

[0188] Substitute ε yc into the strain compatibility equation, the relative compressive zone height ξ fsyb corresponding to limit I can be obtained, which is ξ fsyb can be expressed as a function related to corrosion rate:

[0189]

[0190] According to ξ fsyb , the strain value ε f of CFRP corresponding to limit I can be obtained:

[0191]

[0192] Substitute the strain value ε f of CFRP and the yield stress f yc (η s ) of corroded reinforcement into the force equilibrium equation, a cubic equation about η s can be obtained. The solution of η s is 0.9915, 1.0120 or-1.2103, there is no solution in the range of 0 to 0.8 and the minimum solution is less than 0, which means limit I does not exist, and η f syb = 0. The relative compressive zone height ξ fsyb = 0.4224.

[0193] 22) Calculation of limit II corrosion rate η f shb and limit II relative compressive zone height ξ fsyb

[0194] Considering the strengthening strain with the existence of yield platform, since the tensile reinforcement in L1 beam is ribbed reinforcement and the corrosion mode is accelerated corrosion, η s,cr = 0.3, and the strengthening strain of corroded reinforcement is:

[0195]

[0196] Substitute ε shc into the strain compatibility equation, the relative compressive zone height ξ fshb corresponding to limit II can be obtained, which is ξ fshb can be expressed as a function related to corrosion rate:

[0197]

[0198] According to ξ fshbThe strain value ε of the CFRP corresponding to the limit II can be obtained f :

[0199]

[0200] The strain value ε of the CFRP corresponding to the limit II can be obtained f , the yield stress f of the corroded steel bar yc (η s ) into the force balance equation, a quartic equation about η s can be obtained. The solution of η s is 0.2144, 0.6373, 1.0027 or 1.0057. Taking η f syb <η s <η s,cr The smaller solution in the range is taken as the limit corrosion rate η f shb of the limit II, when η f shb = 0.2144, the relative compressive zone height ξ fshb = 0.1954.

[0201] 23) Calculate the limit III corrosion rate η f sub

[0202] The ultimate strain and the ultimate stress of the corroded steel bar are

[0203]

[0204]

[0205] Substitute ε yc into the strain compatibility equation, the relative compressive zone height ξ fsub corresponding to the limit III can be obtained, when ξ fsub can be expressed as a function related to the corrosion rate. According to ξ fsub , the strain value ε of the CFRP corresponding to the limit III can be obtained f

[0206]

[0207] The strain value ε of the CFRP corresponding to the limit III can be obtained f , the ultimate stress f of the corroded steel bar uc (η s ) into the force balance equation, a high-order equation about η s is obtained, through trial calculation, the solution of η s = 0.8785, that is, η f shb <ηs There is no solution within the range <0.8, so we take η. f sub =0.8.

[0208] The limit corrosion rates and corresponding relative compression zone heights of beams L2, L3, and L4 were calculated according to the above steps, as shown in Table 3.

[0209] (3) Predicting the failure mode of CFRP-reinforced corroded reinforced concrete beams

[0210] The corrosion rates of the reinforcing steel in beams L1, L2, and L4 are within the limit I corrosion rate η. f syb and the boundary II corrosion rate η f shb Between these parameters, the flexural failure mode of these three CFRP-reinforced corroded reinforced concrete beams was determined to be mode ②; the corrosion rate of the steel reinforcement in beam L3 was located at the boundary II corrosion rate η. f shb and the corrosion rate η of boundary III f sub Between these parameters, the flexural failure mode of this CFRP-reinforced corroded reinforced concrete beam was determined to be mode ③. Upon flexural failure, the concrete in all beams was crushed, and the stress states of the CFRP and tensile reinforcement are shown in Table 4.

[0211] Table 4 Limiting corrosion rate and bending failure mode

[0212]

[0213] (4) Calculate the flexural bearing capacity and relative compression zone height of CFRP-reinforced corroded reinforced concrete beams under the predicted failure mode.

[0214] 41) Beam L1:

[0215] ε c t =ε cu At this point, the strain of the corroded steel reinforcement and the strain of the CFRP are expressed as a function of the relative height of the compression zone:

[0216]

[0217]

[0218] At this time σ sc =f yc (η s ), will σ sc and ε f Substituting into the force equilibrium equation, we obtain a quadratic equation in ξ:

[0219] 987000ξ 2 -91449.2420ξ-11542.92955=0

[0220] Solving for ξ, we get ξ = 0.2123, ε f =0.009135, at this time the flexural bearing capacity of the CFRP-reinforced corroded reinforced concrete beam is:

[0221] M u =α1f c bξh(h0-0.5ξh)+E f ε f A f (h-h0)=22.37kN·m

[0222] 42) Beam L3:

[0223] The bending failure mode of beam L3 is mode ③, and the calculation steps for its bending bearing capacity are as follows:

[0224] ε c t =ε cu At this point, the strain of the corroded steel reinforcement and the strain of the CFRP are expressed as a function of the relative height of the compression zone:

[0225]

[0226]

[0227] At this time σ sc =f yc (η s )+E shc (ε sc -ε shc ), where E shc and ε shc The stress-strain relationship of the corroded steel bars can be used to determine σ. sc and ε f Substituting into the force equilibrium equation, we obtain a quadratic equation in ξ:

[0228] 709485ξ 2 -76826.7866ξ-12890.6423=0

[0229] Solving for ξ, we get ξ = 0.1994, ε f =0.009940, at this time the flexural bearing capacity of the CFRP-reinforced corroded reinforced concrete beam is:

[0230] M u =α1f c bξh(h0-0.5ξh)+Ef e f A f (h-h0)=22.23kN.m

[0231] The calculation steps of the flexural bearing capacity of the beams L2 and L4 are similar to those of the beam L1. According to the above steps, the flexural bearing capacities of the four CFRP cloth reinforced corroded reinforced concrete beams are calculated, as shown in Table 5.

[0232] Table 5 Test value and calculated value of flexural bearing capacity

[0233]

[0234] (5) Review of failure mode and approval of flexural bearing capacity of CFRP cloth reinforced corroded reinforced concrete beam

[0235] 1) The flexural bearing capacity and failure mode of the beam L1 are reviewed, ξ = 0.2123, ξ fu = 0.1840, at this time, ξ > ξ fu , the CFRP is in an elastic state, and the bearing capacity of the CFRP reinforced corroded reinforced concrete beam obtained by the above calculation is true and the failure mode is established.

[0236] 2) The flexural bearing capacity and failure mode are reviewed, ξ = 0.1994, ξ fu = 0.1840, at this time, ξ > ξ fu , the CFRP is in an elastic state, and the bearing capacity of the CFRP cloth reinforced corroded reinforced concrete beam obtained by the above calculation is true and the failure mode is established.

[0237] The review steps of the flexural bearing capacity and failure mode of the beams L2 and L4 are similar to those of the beam L1. According to the above steps, all the flexural bearing capacities are true values. As shown in Table 4, the average value of the ratio M u,cal / M u,exp of the calculated value to the test value of the flexural bearing capacity is 0.95775, the sample standard deviation is 0.08667, and the coefficient of variation is 0.09049. This shows that the practical calculation method for the flexural bearing capacity of the CFRP cloth reinforced corroded reinforced concrete beam provided by the application has high accuracy and strong practicability.

[0238] The above relates to a specific embodiment of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the application, and these modifications or replacements should be covered in the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A method for calculating the flexural capacity of a CFRP sheet reinforced corroded reinforced concrete beam, characterized by, The method comprises the following steps: 1) determining the basic parameters of the CFRP cloth reinforced corroded reinforced concrete beam and the CFRP cloth; 2) calculating the limit parameters of the CFRP cloth reinforced corroded reinforced concrete beam based on the basic parameters in step 1); 3) predicting the failure mode of the CFRP cloth reinforced corroded reinforced concrete beam based on the result of step 2); 4) calculating the flexural bearing capacity of the CFRP cloth reinforced corroded reinforced concrete beam and the relative height of the compression zone under the predicted failure mode; 5) rechecking the failure mode and checking the flexural bearing capacity of the CFRP cloth reinforced corroded reinforced concrete beam according to the results of steps 3) and 4). The failure mode of the CFRP cloth reinforced corroded reinforced concrete beam comprises: When Mode 1 is determined, i.e. the CFRP sheet is not pulled off, the corroded steel bar is elastic, and the concrete in the compression zone is crushed. When Mode 2, i.e. the CFRP sheet is not pulled off, the corroded steel bar is yielded, and the concrete in the compression zone is crushed. When Mode 3 is determined, i.e. the CFRP sheet is not pulled off, the corroded steel bars are strengthened, and the concrete in the compression zone is crushed. When Mode IV, i.e. the CFRP sheet is not pulled off, the corroded steel bar is pulled off, and the concrete in the compression zone is crushed. Wherein, the bending resistance M of mode ①, mode ② and mode ③ u Is solved by substituting the relative compression zone height ξ and CFRP tensile strain ε f (ξ) into the bending moment balance equation; Mode IV is divided into two subcategories: A) the CFRP is in the elastic state and the concrete is not crushed when the steel bar is pulled off, and the flexural capacity of the CFRP reinforced corroded reinforced concrete beam is M u1 ; B) the CFRP is in the elastic state and the concrete is crushed after the steel bar is pulled off, and the flexural capacity of the CFRP reinforced corroded reinforced concrete beam is M u2 ; the flexural capacity of the CFRP reinforced corroded reinforced concrete beam corresponding to mode IV is M u , which is the larger value of M u1 and M u2 . The specific calculation steps are as follows: 1) take the relative compression zone height ξ = ξ fsub , the corrosion reinforcement strain ε sc = ε suc (η s ), where ξ fsub is the relative compression zone height corresponding to the limit corrosion rate III, ε suc (η s ) is the limit strain of the corrosion reinforcement, and the deformation compatibility equation is substituted to obtain the CFRP cloth tensile strain value ε f (ξ) related to the relative compression zone height; 2) Stress of corroded steel bar σ sc = f uc (η s ), where f uc (η s ) ultimate stress of corroded steel bar, the sum of the tension of corroded steel bar and the tension of CFRP sheet, the moment at the point of the compressive force of concrete, the flexural capacity of CFRP sheet reinforced corroded steel bar concrete beam in case A u1 , the calculation formula is shown as follows: 3) Let the concrete strain at the edge of the compression zone ε c t = ε cu , where ε cu is the ultimate compressive strain of the concrete, substitute into the deformation compatibility equation to obtain the CFRP strain ε f (ξ), take the corroded steel bar stress σ sc = 0, calculate the relative compression zone height ξ, and substitute the relative compression zone height ξ into the moment equilibrium equation to solve the flexural capacity M u2 of the CFRP-reinforced corroded reinforced concrete beam in case B; The basic parameters of the CFRP cloth reinforced pre-corrosion reinforced concrete beam and the CFRP cloth include a cross section width b, a cross section height h, an effective cross section height h0, a concrete strength grade, a concrete compressive strength f c , a concrete tensile strength f t , a concrete elastic modulus E c , an initial bending moment M i , a tensile edge concrete strain ε under the initial bending moment i , a type of deformed or smooth round tensile and compressive reinforcement, an average corrosion rate η of the tensile reinforcement s , an initial reinforcement area A of the tensile reinforcement s0 , an elastic modulus E of the non-corrosion tensile reinforcement s0 , a yield strength f y0 , an ultimate strength f u0 , a yield strain ε y0 , a hardening strain ε sh0 , an ultimate strain ε u0 , an ultimate tensile strain ε of the CFRP cloth fu , a CFRP cloth reinforcement rate ρ f , and an elastic modulus E of the CFRP cloth f ; The limit parameters of the CFRP cloth reinforced corroded reinforced concrete beam include limit I corrosion rate Limit II corrosion rate Limit III corrosion rate Limit I relative compression zone height ξ fsyb , limit II relative compression zone height ξ fshb , limit III relative compression zone height ξ fsub , and limit IV relative compression zone height ξ fu .

2. The method for calculating the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beams according to claim 1, characterized in that, The limit I represents that the corroded steel bar starts to yield and the compression zone concrete is crushed when the beam is flexurally broken, and the CFRP cloth is not broken; the limit II represents that the corroded steel bar starts to strengthen and the compression zone concrete is crushed when the beam is flexurally broken, and the CFRP cloth is not broken; the limit III represents that the corroded steel bar is broken and the compression zone concrete is crushed at the same time when the beam is flexurally broken, and the CFRP cloth is not broken; and the limit IV represents that the CFRP cloth is broken and the compression zone concrete is crushed at the same time when the beam is flexurally broken.

3. The method for calculating the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beams according to claim 2, characterized in that, Corrosion rate of limit I and relative compressed zone height ξ of limit I fsyb The calculation steps include: a1) the strain of the corroded reinforcement ε sc = ε yc (η s ), the stress of the corroded reinforcement σ sc = f yc (η s ), the strain of the concrete at the edge of the compression zone ε c t = ε cu , where ε yc (η s ) and f yc (η s ) are the yield strain and the yield stress of the corroded reinforcement, respectively, and ε cu is the ultimate compressive strain of the concrete, the relative compression zone height ξ fsyb of the limit I is calculated according to the deformation compatibility equation; a2) Calculate the CFRP strip tensile strain ε according to the deformation compatibility equation f ; a3) strain of corroded steel bar ε sc , stress of corroded steel bar σ sc , tensile strain of CFRP ε f , substitute into force balance equation, get a cubic equation about η s , solve the cubic equation, take the minimum solution in the range of 0-0.8 as the limit corrosion rate of the limit I If there is no solution in the range of 0-0.8 and the minimum solution is negative, take If there is no solution in the range of 0-0.8 and the minimum solution is greater than 0.8, take 4. The method for calculating the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beams according to claim 2, characterized in that, Corrosion rate of limit II and relative compressed zone height ξ of limit II fshb The calculation steps include: b1) Take the strain ε of the corroded steel bar sc =ε shc (η s ), stress σ of corroded steel bars sc =f yc (η s ) and the concrete strain ε at the edge of the compression zone of the section c t =ε cu , where ε shc (η s ) and f yc (η s ε represents the strengthening strain and yield stress of the corroded steel reinforcement, respectively. cu Given the ultimate compressive strain of concrete, solve for the relative height ξ of the compression zone at boundary II using the deformation compatibility equation. fshb ; b2) obtaining the CFRP sheet tensile strain ε according to the deformation compatibility equation f ; b3) the strain ε of the corroded reinforcement sc b4) the stress σ of the corroded reinforcement sc b5) the tensile strain ε of the CFRP sheet f Substituting the force balance equation, according to the stress-strain relationship of the corroded reinforcement and the force balance equation, a quartic equation of η s is obtained, and by taking (1-1.092η s ) / (1-η s )=1 to simplify, a quadratic equation of η is obtained. The solution of the original equation or the simplified equation is taken, and the minimum solution in the range of 0<η If there is no solution in the above range, η 5. The method for calculating the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beams according to claim 2, characterized in that, Corrosion rate of limit III and relative height of the compression zone ξ fsub The calculation steps include: c1) the strain of the corroded reinforcement ε sc = ε suc (η s ) + ε sc (η uc ) + ε s (η c ) and the strain of the concrete at the edge of the compression zone ε t = ε cu , where ε suc (η s ), ε uc (η s ) and ε cu are the ultimate strain of the corroded reinforcement, the ultimate stress of the corroded reinforcement and the ultimate compressive strain of the concrete, respectively; the relative compression zone height ξ fsub of the limit III is solved according to the deformation compatibility equation; c2) obtaining the CFRP sheet tensile strain ε from the deformation compatibility equation f ; c3) the strain ε of the corroded reinforcement sc c4) the stress σ of the corroded reinforcement sc c5) the tensile strain ε of the CFRP sheet f c6) the stress σ of the CFRP sheet s c7) the force equilibrium equation c8) the equation for η c9) the equation for η 6. The method for calculating the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beams according to claim 2, characterized in that, Relative compressed zone height ξ of limit IV fu The calculation steps are: Let ε be the tensile strain of CFRP sheet f = ε fu , ε c be the strain of the concrete at the edge of the compression zone t = ε cu , where ε fu is the ultimate tensile strain of CFRP sheet, ε cu is the ultimate compressive strain of concrete, substitute the deformation compatibility equation, and solve the limit IV relative to the compression zone height ξ fu .

7. The method for calculating the flexural capacity of CFRP sheet reinforced corroded reinforced concrete beams according to claim 1, characterized in that, In step 5), the specific content of rechecking the failure mode and checking the flexural bearing capacity of the CFRP cloth reinforced corroded reinforced concrete beam is: 1) if it is judged that ξ ≥ ξ fu then the failure mode determined in step 3) is true, and the bearing capacity calculated in step 4) is true. 2) If ξ < ξ fu , the real failure mode is mode ⑤, and the flexural capacity of the CFRP sheet-strengthened corroded reinforced concrete beam is calculated under mode ⑤. Mode ⑤ includes two types: A) CFRP is pulled off, and the concrete is not crushed. At this time, the flexural capacity of the CFRP sheet-strengthened corroded reinforced concrete beam is M u1 ; B) CFRP is pulled off, and the CFRP sheet-strengthened corroded reinforced concrete beam degenerates into an un-strengthened corroded reinforced concrete beam, and the corresponding flexural capacity is M uc . The flexural capacity of the CFRP sheet-strengthened corroded reinforced concrete beam is M u , which takes the larger value of M u1 and M uc .

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