CN105426691B - Bar planting method reinforces the computational methods for the Ultimate flexural strength for putting core beam - Google Patents

Abstract

The invention proposes a method for calculating the ultimate bearing capacity of a positive cross-section of a core-placed beam reinforced by planting tendons, which belongs to the technical field of beam reinforcement. The calculation method includes the following steps: (1) Make basic assumptions about the reinforcement process; (2) Calculate the stress-strain relationship of the cross-section of the core material under the failure conditions of each material; (3) Calculate the stress-strain relationship of the core material under the failure conditions of each material. The height of the compression zone of the cross section; (4) Calculate the height of the plastic development of the compression zone of the cross section of the core material under the failure conditions of each material; The height of the compression zone and the height of the plastic development of the compression zone are used to calculate the flexural bearing capacity of the normal section of the reinforced core beam under the corresponding material failure conditions, and the ultimate bearing capacity of the normal section of the reinforced core beam considering the plastic development is obtained. The invention can effectively calculate the limit bearing capacity of the normal section of the core-placed beam reinforced by the planting bar method considering the plastic development, and provides powerful theoretical guidance for engineering application.

Description

The Calculation Method of the Ultimate Bearing Capacity of the Positive Section of the Core-set Beam Strengthened by Planting the Reinforcement Method

technical field

The invention belongs to the technical field of beam reinforcement, and relates to a calculation method of the ultimate bearing capacity, in particular to a calculation method of the ultimate bearing capacity of reinforced cored beams.

Background technique

The vast majority of ancient Chinese buildings belong to wooden structure buildings. Due to long-term exposure to the sun and rain, termite erosion, and corrosion and aging of component surfaces, the safety of these ancient buildings is decreasing year by year. At present, the reinforcement and repair of wooden components of ancient buildings generally adopts the replacement of whole beams, or grouting filling of holes and cracks. These methods have improved the safety of ancient buildings to a certain extent; their disadvantages are that the beams and columns of the building need to be unloaded before replacing the beams and columns, which has potential safety hazards, and the construction speed is slow and the cost is high. In addition, the appearance of the replaced components is obviously different from the original part, which violates the principle of "repairing the old as the old" for ancient buildings with cultural relics value.

The corrosion of beams and square members in wooden structures mainly occurs at both ends and upper parts of the members, while the beam members near the patio, door and corridor are generally more severely damaged than the beam members inside the building, especially some ancestral halls, Huizhou buildings such as government offices and temples have been in disrepair for a long time, and there are many phenomena such as rain leakage and water leakage at the eaves, resulting in a special form of damage when the appearance of the beam components is intact but the pith core has rotted. The phenomenon is also more common.

There are a large number of theoretical and experimental analyzes at home and abroad for the methods and technologies of wooden beam reinforcement and repair, but basically the reinforcement methods such as directly pasting steel, cloth and ribs on the surface of the original beam members are used to improve the damage. The bearing capacity or stiffness of the specimen is the main goal of the reinforcement technology, and the reinforcement treatment method is unidirectional, irreversible, and cannot be reinforced twice, and has a great influence on the appearance of the wooden beam. What is especially important is that how to conduct systematic research on the structural system design theory of the strengthening technology that can protect the appearance of the building and can be reinforced twice. At present, there is no theoretical basis and analysis and design method to guide engineering applications, let alone Corresponding specifications and procedures can be followed. Especially when calculating the ultimate bearing capacity of strengthened beams, usually only the ultimate bearing capacity of elastic development is considered, and the ultimate bearing capacity of plastic development is not considered, which cannot objectively reflect the performance of reinforced beams and cannot provide a reasonable theoretical basis for engineering applications .

Contents of the invention

The purpose of the present invention is to provide a method for calculating the ultimate bearing capacity of the normal section of the beam reinforced by the reinforcement technology capable of protecting the appearance of the building and capable of secondary reinforcement.

In order to achieve the above object, the solution of the present invention is:

A calculation method for strengthening the ultimate bearing capacity of the front section of a core-placed beam by planting ribs, wherein the ribs are used as reinforcement materials, implanted at the bottom of the core material to strengthen the core material, and the core material is then arranged on the tensile surface of the outer shell of the beam area to reinforce said beam; said method comprising the steps of:

(1) Make basic assumptions about the reinforcement process;

(2) Calculating the stress-strain relationship of the cross-section of the core material in the case of failure of each material in the reinforced core beam;

(3) calculating the height of the compression zone of the cross-section of the core material and the height of the plastic development of the compression zone of the cross-section of the core material under each material failure situation;

(4) According to the height of the compression zone of the cross-section of the core material and the height of the plastic development of the compression zone under each material failure situation, calculate the bending load of the normal section of the reinforced core beam under each material failure situation Force, to obtain the ultimate bearing capacity of the normal section of the strengthened core beam considering the plastic development.

The bars are CFRP bars or steel bars.

The basic assumptions of the step (1) include:

(11) Assume that the contribution of the shell of the beam to the reinforcement of the core-set beam is zero;

(12) It is assumed that the cross-section of the core beam remains flat before and after deformation;

(13) Assuming that before the cracking of the tensile zone of the core beam, the reinforcement material and the core material are coordinated and deformed, and there is no bond-slip phenomenon;

(14) Assume that the compression constitutive model of the core material is an ideal elastoplastic model, and the tensile constitutive model is a linear elastic model;

(15) When the reinforcement is a CFRP reinforcement, it is assumed that the constitutive model of the CFRP reinforcement is a linear elastic model; when the reinforcement is a reinforcement, it is assumed that the constitutive model of the reinforcement is an ideal elastic-plastic model.

Described core material is wood, comprises wood fiber; Described each material destruction situation comprises:

Damage caused by the breakage of wood fibers of the core material under tension;

Destruction caused by the wood fibers of the compressed core material reaching the ultimate strain;

When the reinforcement is a CFRP reinforcement, the damage caused by the CFRP reinforcement reaching the ultimate strength; when the reinforcement is a steel bar, the damage is caused by the steel bar yielding and the wood fiber of the core material being pulled apart and fractured.

Described step (2) comprises:

Calculate the stress-strain relationship of the cross-section of the core material under the condition that the wood fiber of the tensioned core material breaks and causes damage according to the following formula:

in: Indicates the ultimate tensile strain of the wood fiber of the core material;

Indicates the yield compressive strain of the wood fiber of the core material;

h ₀ represents the distance from the stressed geometric center of the rib to the compressed edge of the core material;

x _c represents the height of the compression zone of the cross-section of the core material;

x _cp represents the height of the plastic zone development in the compression zone of the cross-section of the core material;

Indicates the ultimate tensile stress of the wood fiber of the core material under the condition of considering the strength reduction;

Indicates the yield compressive stress of the wood fibers of the core material without considering the strength reduction;

R _σ represents the ratio of the maximum tensile stress to the maximum compressive stress of the wood fibers of the core material;

Calculate the stress-strain relationship of the cross-section of the core material under the condition that the wood fiber of the core material under compression reaches the ultimate compressive strain and causes damage:

in: Indicates the ultimate compressive strain of the wood fiber of the core material;

_γε represents the ratio of the ultimate plastic strain to the elastic strain of the wood fibers of the core material;

When the reinforcement is a CFRP reinforcement, the stress-strain relationship of the cross-section of the core material is calculated according to the following formula when the CFRP reinforcement reaches the ultimate strength and causes damage:

in: Indicates the ultimate tensile strain in the CFRP tendon constitutive model;

Indicates the ultimate tensile stress in the CFRP tendon constitutive model;

α _E represents the ratio of the modulus of elasticity of the CFRP tendon to the modulus of elasticity of the core material;

When the reinforcement is a reinforcement, the stress-strain relationship of the cross-section of the core is calculated by the following formula under the situation that the reinforcement yields and the wood fiber of the core breaks and causes damage:

In the step (3), the height of the compression zone of the cross-section of the core material is calculated in the case of damage to each material, and the height of the compression zone of the cross-section of the core material includes: in the case of damage caused by the fracture of the wood fiber of the core material under tension, the When the wood fibers of the compressed core material reach the ultimate compressive strain and cause damage, when the CFRP reinforcement reaches the ultimate strength and cause damage, when the reinforcement is a steel bar, the steel bar yields, the core material The height x _c of the compression zone of the cross-section of the core material in the case of damage caused by tensile fracture of the wood fibers:

Where: F _i represents the internal force of each material or component;

h represents the height of the cross-section of the core material;

σ ^w (x _c ) represents the stress of the wood fiber at the height x _c of the compression zone of the cross-section of the core material;

b(x _c ) represents the section width at the height x _c of the compression zone of the cross section of the core material;

Indicates the tensile stress of the tensile reinforced material;

A ^F represents the area of the tension-strengthened material.

In the step (3), the height of the plastic development of the compression zone of the cross-section of the core material under the conditions of material failure calculated in the step (3) includes: combining the cross-section of the core material under the conditions of material failure calculated in the step (2) Calculate the height x _cp of the plastic development in the compression zone of the cross-section of the core material under the failure conditions of each material.

Described step (4) comprises:

The flexural bearing capacity of the normal section of the reinforced core beam under the failure conditions of each material is calculated according to the following formula:

Among them: M represents the flexural bearing capacity of the normal section of the reinforced core beam;

b represents the width of the cross-section of the core material;

x _c is calculated according to the value of x _c under the corresponding damage situation in step (3);

x _cp is calculated according to the value of x _cp under the corresponding damage situation in step (3).

The step (4) also includes: taking the smallest value among the normal section flexural bearing capacity of the reinforced core beam under each material damage situation, taking the minimum value as the normal section of the reinforced core beam considering plastic development ultimate carrying capacity.

Due to the adoption of the above scheme, the beneficial effects of the present invention are: the present invention proposes a method for calculating the ultimate bearing capacity of the positive section of the core beam reinforced by the method of planting bars, which provides theoretical guidance for the design of reinforcing the core beam with the method of planting bars, It is ensured that the core beam strengthened in this way can meet the design requirements, thereby effectively protecting the integrity of the building appearance, the strength meets the requirements and can be reinforced again.

Description of drawings

Figure 1a is a schematic diagram of a core material reinforced by planting bars in an embodiment of the present invention;

Figure 1b is a schematic diagram of the original beam shell in an embodiment of the present invention;

Figure 1c is a schematic diagram of a reinforced core beam obtained after reinforcing the original beam shell of Figure 1b with the core material of Figure 1a;

Fig. 2 is the graph of the constitutive relation model of core material in the embodiment of the present invention;

Fig. 3 is the graph of the constitutive relation model of CFRP bar in the embodiment of the present invention;

Fig. 4 is the graph of the constitutive relation model of common reinforcing bar in the embodiment of the present invention;

Fig. 5a is one of the calculation schematic diagrams of the height of the compression zone of the cross section of the core material in the embodiment of the present invention;

Fig. 5b is the second schematic diagram of the calculation of the height of the compression zone of the cross section of the core material in the embodiment of the present invention;

Fig. 6a is one of the schematic diagrams for calculating the flexural bearing capacity of the front section of the core wood beam in the embodiment of the present invention;

Fig. 6b is the second schematic diagram of the calculation of the flexural bearing capacity of the front section of the core wood beam in the embodiment of the present invention;

Fig. 6c is the third schematic diagram of calculating the flexural bearing capacity of the front section of the cored wood beam in the embodiment of the present invention.

In the attached drawings: 1. Rib; 2. Core material; 3. Original beam shell.

detailed description

The present invention will be further described below in conjunction with the embodiments shown in the accompanying drawings.

Aiming at the lack of theoretical research on technologies capable of protecting the appearance of ancient buildings and strengthening beams twice in the prior art, the present invention proposes a calculation method for calculating the ultimate bearing capacity of the positive section of cored beams reinforced by planting tendons. In the technology of strengthening the core beam by planting reinforcement, the reinforcement 1 is used as the reinforcement material to reinforce the core material 2, and the reinforced core material 2 is placed in the tensile area of the original beam shell 3. Wherein, the process of reinforcing the core material by adopting the rib planting method is to insert the rib 1 into the bottom of the core material 2 to reinforce the core material 2 . Figure 1a is a schematic diagram of the core material reinforced with CFRP (carbon fiber reinforced composite material) plates; Figure 1b is a schematic diagram of the original beam shell, in which the vacant area is the tension area; Figure 1c is a reinforcement diagram of the reinforced core material in Figure 1a 1b Schematic diagram of the reinforced core beam obtained after the original beam shell. In this embodiment, the core material 2 is wood, including wood fibers.

The method for calculating the ultimate bearing capacity of the positive section of the core beam reinforced by the planting reinforcement method proposed by the present invention comprises the following steps:

In the first step, the following basic assumptions are made for the reinforcement process:

1) Assume that the contribution of the original beam shell to the reinforced core-set beam is not considered, that is, the contribution of the original beam to the reinforced core-set beam is assumed to be zero;

2) Assume that the cross-section of the reinforced core beam remains flat before and after deformation, that is, the flat section assumption is met;

3) It is assumed that before the tensile zone of the reinforced core beam cracks, the reinforcement material (i.e. tendons) and the core material are coordinated and deformed, and there is no bond-slip phenomenon;

4) It is assumed that the compression constitutive model of the core material is an ideal elastic-plastic model, and the tensile constitutive model is a linear elastic model, as shown in Figure 2. Among them, the compressive modulus of elasticity of the core material and tensile modulus of elasticity take the same value, Pick in, is the ultimate compressive strain of the wood fibers of the core material, is the compressive strain at yield of the wood fibers of the core material, is the ultimate tensile strain of the wood fibers of the core material. Among Fig. 2, ε ^w represents the strain of the wood fiber of core material; σ ^w represents the stress of the wood fiber of core material; Indicates the ultimate compressive stress of the wood fiber of the core material; Indicates the ultimate tensile stress of the wood fiber of the core material.

5) When the reinforcement is a CFRP reinforcement, assuming that the CFRP reinforcement only considers the strength along the wood fiber direction of the core material, the stress is equal to the product of the strain and its elastic modulus, but its absolute value is not greater than its corresponding strength design value, the constitutive model Select the linear elastic model, as shown in Figure 3. in, Indicates the ultimate tensile strain of the CFRP tendon; Indicates the ultimate tensile stress of the CFRP tendon; Represents the tensile elastic modulus of CFRP tendons; σ ^F represents the stress of CFRP tendons; ε ^F represents the strain of CFRP tendons.

When the bar is an ordinary steel bar, assuming that the stress of the ordinary steel bar is equal to the product of its strain and its elastic module, but its absolute value is not greater than its corresponding design strength design value, the ultimate tensile strain Taking 0.01, the constitutive model chooses the ideal elastoplastic model, as shown in Figure 4. In Fig. 4, σ ^s represents the stress of common steel bar; Indicates the tensile strain at yield of common steel bar; Indicates the yield compressive stress of ordinary steel bar; Indicates the yield compressive strain of ordinary steel bar; Indicates the tensile stress at yield of ordinary steel bar; ε ^s indicates the strain of ordinary steel bar; Represents the tensile modulus of elasticity of ordinary steel bars.

The second step is to calculate the stress-strain relationship of the cross-section of the core material in the case of failure of each material of the strengthened core beam based on the assumption of a plane section, including:

Calculate the stress-strain relationship of the cross-section of the core material under the condition that the wood fiber of the tensioned core material breaks and causes damage according to the following formula:

in: Indicates the ultimate tensile strain of the wood fiber of the core material;

Indicates the yield compressive strain of the wood fiber of the core material;

h ₀ represents the distance from the stressed geometric center of the rib to the compressed edge of the core material;

x _c represents the height of the compression zone of the cross-section of the core material;

x _cp represents the plastic development height of the compression zone of the cross-section of the core material;

Indicates the ultimate tensile stress of the wood fibers of the core material when the strength reduction is considered (that is, when the defects such as knots, holes and shrinkage cracks in the tensile area of the core material are considered to reduce the tensile strength);

Indicates the yield compressive stress of the wood fibers of the core material without considering the strength reduction (that is, without considering the reduction of the tensile strength by defects such as knots, holes and shrinkage cracks in the tensile area of the core material);

R _σ represents the ratio of the maximum tensile stress to the maximum compressive stress of the wood fibers of the core material.

Calculate the stress-strain relationship of the cross-section of the core material under the condition that the wood fiber of the core material under compression reaches the ultimate compressive strain and causes damage:

in: Indicates the ultimate compressive strain of the wood fiber of the core material;

γ _ε represents the ratio of the ultimate plastic strain to the elastic strain of the wood fibers of the core material.

When the reinforcement is a CFRP reinforcement, the stress-strain relationship of the cross-section of the core material is calculated according to the following formula when the CFRP reinforcement reaches the ultimate strength and causes failure:

in: Indicates the ultimate tensile strain in the CFRP plate constitutive model;

Indicates the ultimate tensile force in the CFRP plate constitutive model;

α _E represents the ratio of the elastic modulus of the CFRP plate to the elastic modulus of the core material.

When the bar is ordinary steel bar, the stress-strain relationship of the cross section of the core material is calculated by the following formula when the planting material of the ordinary steel bar yields and the wood fiber of the core material breaks and causes damage:

In the third step, according to the various formulas in the second step and the static equilibrium conditions of the cross-section, the following formulas are used to calculate the damage of each material, that is, in the case of damage caused by the breakage of the wood fiber of the core material under tension, the When the wood fiber of the material reaches the ultimate compressive strain and causes damage, when the reinforcement is CFRP reinforcement, the CFRP reinforcement reaches the ultimate strength and causes damage, when the reinforcement is ordinary reinforcement, the ordinary reinforcement yields, and the wood fiber of the core material breaks In the case of damage caused by cracking, the height x _c of the compression zone of the cross-section of the core material is shown in Figure 5a and Figure 5b:

Where: F _i represents the internal force of each material or component;

h represents the height of the cross-section of the core material;

σ ^w (x _c ) represents the stress of the wood fiber at the height x _c of the cross section of the core material;

_b (xc) represents the width of the section at the height _xc of the cross section of the core material;

Indicates the tensile stress of the tensile reinforced material;

A ^F represents the area of the tension-strengthened material.

In Figure 5b, Indicates the compressive strain of the wood fibers of the core material; Indicates the tensile strain of the wood fiber of the core material; Indicates the tensile strain of the tension-reinforced material.

The fourth step is to combine the stress-strain relationship of the cross-section of the core material under the failure conditions calculated in the second step to calculate the plastic development height x _cp of the compression zone of the cross-section of the core material under each material failure condition .

The fifth step, as shown in Fig. 6a, Fig. 6b and Fig. 6c, calculate the flexural bearing capacity of the normal section of the strengthened core beam according to the following formula:

Among them: M represents the flexural bearing capacity of the normal section of the reinforced core beam;

b represents the width of the cross-section of the core material;

x _c is calculated according to the value of x _c in the corresponding damage situation in the third step;

x _cp is calculated according to the value of x _cp under the corresponding damage situation in the fourth step.

Among the calculated flexural bearing capacity of the normal section of the reinforced core beam under various material failure conditions, the smallest value is taken as the ultimate bearing capacity of the normal section of the reinforced core beam considering plastic development.

In Fig. 6a, a represents the distance from the stressed geometric center of the rib to the tensioned edge of the core material. F ^F represents the resultant force of reinforcement materials (ordinary steel bars or CFRP bars); Indicates the tensile stress of the wood fibers of the core material.

The ultimate bearing capacity of the front section of the core-laid beam obtained by the above method can be used as a guide for relevant theoretical research and engineering application, and assist in obtaining a reinforced core-laid beam that can meet the design requirements.

Generally, the core-laid beams strengthened by the planting reinforcement method after design completion shall meet the following functional requirements within the specified design service life:

(1) It can withstand various possible actions during normal construction and normal use;

(2) It can meet the control requirements of various indicators of the structure during normal construction and normal use;

(3) Good working performance in normal use;

(4) Sufficient durability under normal maintenance;

(5) The necessary overall stability can still be maintained during and after the accidental events specified in the design.

The above-mentioned requirements for the function of cored beam structural members strengthened by planting reinforcement method are essentially to have sufficient strength, be able to withstand the internal force generated by the most unfavorable load effect, and meet the limit state requirements of bearing capacity. In addition, it is also necessary to consider the economy and operability of the design scheme.

The design of cored beam structural members strengthened by planting reinforcement method is mainly carried out according to the following steps, and an economical, reasonable and feasible design scheme often needs to be revised and calculated several times to obtain:

(1) Determine the secondary internal force of the structure;

(2) Preliminarily determine the cross-sectional size of the reinforced core wood beam and the cross-sectional size and length of the planting bar material according to the use requirements and the proposed overall plan and structural form, referring to the existing design and relevant materials;

(3) Using the internal force analysis model, calculate the combination of load effects and the maximum effect of the control section;

(4) According to the design internal force of the control section under the limit state of bearing capacity and normal service limit state and the preliminary section size, estimate the type, quantity, size and arrangement of planting reinforcement materials, and arrange them reasonably. If the reinforcement material cannot be arranged reasonably, return to step (2) and modify the section size;

(5) Check and calculate the section stress in the construction stage, transportation and installation stage and use stage;

(6) Check the anchorage length.

To sum up, the present invention proposes a calculation method for the ultimate bearing capacity of the front section of the core-set beam reinforced by the planting bar method, which provides theoretical guidance for the design of the core-set beam strengthened by the planting bar method, and ensures that the reinforcement in this way The core beam can meet the design requirements, thereby effectively protecting the integrity of the building appearance, the strength meets the requirements and can be reinforced again.

The above description of the embodiments is for those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described here to other embodiments without creative effort. Therefore, the present invention is not limited to the embodiments herein. Improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims (7)

1. A method of planting ribs to strengthen the calculation method of the positive section ultimate bearing capacity of the core beam, wherein the ribs are used as reinforcement materials, implanted into the bottom of the core material to reinforce the core material, and the core material is then arranged on the outer shell of the beam In the tension zone to strengthen the beam, it is characterized in that: the method includes the following steps: (1) Make basic assumptions about the reinforcement process; (2) Calculating the stress-strain relationship of the cross-section of the core material in the case of failure of each material in the reinforced core beam; (3) calculating the height of the compression zone of the cross-section of the core material and the height of the plastic development of the compression zone of the cross-section of the core material under each material failure situation; (4) According to the height of the compression zone of the cross-section of the core material and the height of the plastic development of the compression zone under each material failure situation, calculate the bending load of the normal section of the reinforced core beam under each material failure situation Force, to obtain the ultimate bearing capacity of the positive section of the strengthened core beam considering the plastic development; The basic assumptions of the step (1) include: (11) Assume that the contribution of the shell of the beam to the reinforcement of the core-set beam is zero; (12) It is assumed that the cross-section of the core beam remains flat before and after deformation; (13) Assuming that before the cracking of the tensile zone of the core beam, the reinforcement material and the core material are coordinated and deformed, and there is no bond-slip phenomenon; (14) Assume that the compression constitutive model of the core material is an ideal elastoplastic model, and the tensile constitutive model is a linear elastic model; (15) when described reinforcement is a CFRP reinforcement, assume that the constitutive model of CFRP reinforcement takes the linear elastic model; When described reinforcement is a reinforcement, assume that the constitutive model of reinforcement selects the ideal elastoplastic model; The material damage scenarios described include: Damage caused by the breakage of wood fibers of the core material under tension; Destruction caused by the wood fibers of the compressed core material reaching the ultimate compressive strain; When the reinforcement is a CFRP reinforcement, the damage caused by the CFRP reinforcement reaching the ultimate strength; when the reinforcement is a steel bar, the damage is caused by the steel bar yielding and the wood fiber of the core material being pulled apart and fractured. 2. The method for calculating the ultimate bearing capacity of the front section of a cored beam reinforced by planting bars according to claim 1, wherein the bars are CFRP bars or steel bars. 3. The method for calculating the ultimate bearing capacity of the front section of a cored beam reinforced by planting bars according to claim 1, characterized in that: the core material is wood and contains wood fibers. 4. the method for planting bars according to claim 1 strengthens the calculation method of the positive cross-section ultimate bearing capacity of cored beams, it is characterized in that: described step (2) comprises: Calculate the stress-strain relationship of the cross-section of the core material under the condition that the wood fiber of the tensioned core material breaks and causes damage according to the following formula: <mrow><mfrac><msubsup><mi>&amp;epsiv;</mi><mrow><mi>t</mi><mi>u</mi></mrow><mi>w</mi></msubsup><msubsup><mi>&amp;epsiv;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup></mfrac><mo>=</mo><mfrac><mrow><msub><mi>h</mi><mn>0</mn></msub><mo>-</mo><msub><mi>x</mi><mi>c</mi></msub></mrow><mrow><msub><mi>x</mi><mi>c</mi></msub><mo>-</mo><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub></mrow></mfrac><mo>=</mo><mfrac><msubsup><mi>&amp;sigma;</mi><mrow><mi>t</mi><mi>u</mi></mrow><mi>w</mi></msubsup><msubsup><mi>&amp;sigma;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup></mfrac><mo>=</mo><msub><mi>R</mi><mi>&amp;sigma;</mi></msub></mrow> in: Indicates the ultimate tensile strain of the wood fiber of the core material; Indicates the yield compressive strain of the wood fiber of the core material; h ₀ represents the distance from the stressed geometric center of the rib to the compressed edge of the core material; x _c represents the height of the compression zone of the cross-section of the core material; x _cp represents the height of the plastic zone development in the compression zone of the cross-section of the core material; Indicates the ultimate tensile stress of the wood fiber of the core material under the condition of considering the strength reduction; Indicates the yield compressive stress of the wood fibers of the core material without considering the strength reduction; R _σ represents the ratio of the maximum tensile stress to the maximum compressive stress of the wood fibers of the core material; Calculate the stress-strain relationship of the cross-section of the core material under the condition that the wood fiber of the core material under compression reaches the ultimate compressive strain and causes damage: <mrow><mfrac><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub><mrow><msub><mi>x</mi><mi>c</mi></msub><mo>-</mo><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub></mrow></mfrac><mo>=</mo><mfrac><mrow><msubsup><mi>&amp;epsiv;</mi><mrow><mi>c</mi><mi>u</mi></mrow><mi>w</mi></msubsup><mo>-</mo><msubsup><mi>&amp;epsiv;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup></mrow><msubsup><mi>&amp;epsiv;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup></mfrac><mo>=</mo><msub><mi>&amp;gamma;</mi><mi>&amp;epsiv;</mi></msub></mrow> in: Indicates the ultimate compressive strain of the wood fiber of the core material; _γε represents the ratio of the ultimate plastic strain to the elastic strain of the wood fibers of the core material; When the reinforcement is a CFRP reinforcement, the stress-strain relationship of the cross-section of the core material is calculated according to the following formula when the CFRP reinforcement reaches the ultimate strength and causes damage: <mrow><mfrac><msubsup><mi>&amp;epsiv;</mi><mrow><mi>t</mi><mi>u</mi></mrow><mi>F</mi></msubsup><msubsup><mi>&amp;epsiv;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup></mfrac><mo>=</mo><mfrac><msubsup><mi>&amp;sigma;</mi><mrow><mi>t</mi><mi>u</mi></mrow><mi>F</mi></msubsup><mrow><msub><mi>&amp;alpha;</mi><mi>E</mi></msub><msubsup><mi>&amp;sigma;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup></mrow></mfrac><mo>=</mo><mfrac><mrow><msub><mi>h</mi><mn>0</mn></msub><mo>-</mo><msub><mi>x</mi><mi>c</mi></msub></mrow><mrow><msub><mi>x</mi><mi>c</mi></msub><mo>-</mo><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub></mrow></mfrac></mrow> in: Indicates the ultimate tensile strain in the CFRP tendon constitutive model; Indicates the ultimate tensile stress in the CFRP tendon constitutive model; α _E represents the ratio of the modulus of elasticity of the CFRP tendon to the modulus of elasticity of the core material; When the reinforcement is a reinforcement, the stress-strain relationship of the cross-section of the core is calculated by the following formula under the situation that the reinforcement yields and the wood fiber of the core breaks and causes damage: <mrow><mfrac><msubsup><mi>&amp;epsiv;</mi><mrow><mi>t</mi><mi>u</mi></mrow><mi>w</mi></msubsup><msubsup><mi>&amp;epsiv;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup></mfrac><mo>=</mo><mfrac><msubsup><mi>&amp;sigma;</mi><mrow><mi>t</mi><mi>u</mi></mrow><mi>w</mi></msubsup><msubsup><mi>&amp;sigma;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup></mfrac><mo>=</mo><mfrac><mrow><msub><mi>h</mi><mn>0</mn></msub><mo>-</mo><msub><mi>x</mi><mi>c</mi></msub></mrow><mrow><msub><mi>x</mi><mi>c</mi></msub><mo>-</mo><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub></mrow></mfrac><mo>.</mo></mrow> 5. the calculation method of reinforcing the positive section ultimate bearing capacity of the core beam according to claim 4, it is characterized in that: in the described step (3), under the condition of calculating each material failure, the transverse direction of the core material The height of the compression zone of the section includes: according to the following formula, when the wood fiber of the tensioned core material breaks and causes damage, and when the wood fiber of the compressed core material reaches the ultimate compressive strain and causes damage, when the When the reinforcement is a CFRP reinforcement, when the CFRP reinforcement reaches the ultimate strength and causes damage, when the reinforcement is a steel reinforcement, the steel reinforcement yields, and the wood fiber of the core material is pulled and cracked to cause damage, the cross-section of the core material is affected. Height x _c of the nip: <mrow><msub><mi>&amp;Sigma;F</mi><mi>i</mi></msub><mo>=</mo><msubsup><mo>&amp;Integral;</mo><mrow><mo>-</mo><mi>h</mi><mo>/</mo><mn>2</mn></mrow><mrow><mi>h</mi><mo>/</mo><mn>2</mn></mrow></msubsup><msup><mi>&amp;sigma;</mi><mi>w</mi></msup><mrow><mo>(</mo><msub><mi>x</mi><mi>c</mi></msub><mo>)</mo></mrow><mi>b</mi><mrow><mo>(</mo><msub><mi>x</mi><mi>c</mi></msub><mo>)</mo></mrow><msub><mi>dx</mi><mi>c</mi></msub><mo>+</mo><msubsup><mi>&amp;sigma;</mi><mi>t</mi><mi>F</mi></msubsup><msup><mi>A</mi><mi>F</mi></msup><mo>=</mo><mn>0</mn></mrow> Where: F _i represents the internal force of each material or component; h represents the height of the cross-section of the core material; σ ^w (x _c ) represents the stress of the wood fiber at the height x _c of the compression zone of the cross-section of the core material; b(x _c ) represents the section width at the height x _c of the compression zone of the cross section of the core material; Indicates the tensile stress of the tensile reinforced material; A ^F represents the area of the tension-strengthened material. 6. the method for planting bars according to claim 5 strengthens the calculation method of the positive section ultimate bearing capacity of the core-set beam, it is characterized in that: described step (4) comprises: The flexural bearing capacity of the normal section of the reinforced core beam under the failure conditions of each material is calculated according to the following formula: <mrow><mi>M</mi><mo>=</mo><msubsup><mi>&amp;sigma;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup><mi>b</mi><mrow><mo>(</mo><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub><mo>(</mo><mrow><msub><mi>x</mi><mi>c</mi></msub><mo>-</mo><mfrac><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub><mn>2</mn></mfrac></mrow><mo>)</mo><mo>+</mo><mfrac><mrow><msup><mrow><mo>(</mo><msub><mi>x</mi><mi>c</mi></msub><mo>-</mo><msub><mi>x</mi>mi><mrow><mi>c</mi><mi>p</mi></mrow></msub><mo>)</mo></mrow><mn>3</mn></msup><mo>+</mo><msup><mrow><mo>(</mo><mi>h</mi><mo>-</mo><msub><mi>x</mi><mi>c</mi></msub><mo>)</mo></mrow><mn>3</mn></msup></mrow><mrow><mn>3</mn><mrow><mo>(</mo><msub><mi>x</mi><mi>c</mi></msub><mo>-</mo><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub><mo>)</mo></mrow></mrow></mfrac><mo>)</mo></mrow><mo>+</mo><mfrac><mrow><msub><mi>&amp;alpha;</mi><mi>E</mi></msub><msubsup><mi>&amp;sigma;</mi><mrow><mi>c</mi><mi>y</mi></mrow><mi>w</mi></msubsup><msup><mi>A</mi><mi>F</mi></msup><msup><mrow><mo>(</mo><mi>h</mi><mo>-</mo><msub><mi>x</mi><mi>c</mi></msub><mo>)</mo></mrow><mn>2</mn></msup></mrow><mrow><msub><mi>x</mi><mi>c</mi></msub><mo>-</mo><msub><mi>x</mi><mrow><mi>c</mi><mi>p</mi></mrow></msub></mrow></mfrac></mrow> Among them: M represents the flexural bearing capacity of the normal section of the reinforced core beam; b represents the width of the cross-section of the core material; x _c is calculated according to the value of x _c under the corresponding damage situation in step (3); x _cp is calculated according to the value of x _cp under the corresponding damage situation in step (3). 7. The calculation method for strengthening the ultimate bearing capacity of the front section of the cored beam by planting reinforcement method according to claim 1, characterized in that: said step (4) also includes: reinforcing under the failure conditions of the obtained materials Among the bending bearing capacity of the normal section of the core beam, the smallest value is taken as the ultimate bearing capacity of the normal section of the reinforced core beam considering plastic development.