A design method for the out-of-plane flexural capacity of brick masonry walls strengthened with externally bonded GFRP vertical strips

Abstract

The application provides a design method of out-of-plane flexural capacity of a brick masonry wall reinforced by externally bonded GFRP vertical strips, the structure of the brick masonry wall reinforced by externally bonded GFRP vertical strips comprises a brick masonry wall, GFRP vertical reinforcing strips, GFRP horizontal anchoring strips and GFRP anchors. The design method comprises the following steps: determining the vertical load and the design value of the out-of-plane bending moment of the brick masonry wall; calculating the GFRP area according to the out-of-plane flexural capacity formula; checking the GFRP reinforcement rate, so that the GFRP reinforcement rate is not less than the minimum reinforcement rate and not more than the maximum reinforcement rate; and determining the number of GFRP strips, the width and the thickness of a single GFRP strip according to the GFRP area. The application can significantly enhance the out-of-plane flexural capacity of the brick masonry wall, thereby providing a new technology and a new idea for the seismic and wind resistance reinforcement of old masonry house walls, and can produce certain economic and social benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of building structure reinforcement, and relates to a general brick masonry building reinforcement design method. BACKGROUND

[0002] Masonry structure refers to a structure built by brick masonry, stone masonry or other block masonry, among which the history of stone masonry and brick masonry structure is particularly long. Since masonry structure has the advantages of easy material procurement and low cost, a large number of masonry structures were built in the early years of the founding of the People's Republic of China.

[0003] The masonry structures in the 1970s and 1980s still exist in large quantities in Chinese cities and towns. With the continuous development of economy and technology, the construction industry has also been constantly progressing. It is found that at the present stage, most of the houses in villages and towns are self-built houses. Due to design defects, poor construction, improper use and other reasons, the buildings cannot meet the normal use, and even are on the verge of destruction. Brick masonry walls generally bear in-plane loads (self-weight, loads transmitted from the upper structure) and out-of-plane loads (wind loads, self-inertia forces generated by earthquake action). The main failure modes are in-plane shear failure and out-of-plane bending failure. The main feature of in-plane failure is mainly diagonal cracks, and the main feature of out-of-plane failure is cracks along the mortar joints. Since the brick masonry material is a block material, the blocks are only bonded by mortar, which leads to insufficient out-of-plane bending resistance of the brick masonry structure, and the out-of-plane collapse of the brick masonry wall becomes a main failure mode of the masonry structure under the action of earthquake. Therefore, it is quite important to reinforce the existing important brick masonry walls and improve the seismic performance.

[0004] At present, the commonly used reinforcement methods for brick masonry structures mainly include: steel wire mesh cement mortar outer layer reinforcement method, concrete or cement mortar spraying reinforcement method, support column or steel support column reinforcement method, and section enlargement reinforcement method. These reinforcement methods can improve the bearing capacity of the structure and improve the seismic performance of the brick masonry wall to a certain extent, but these reinforcement methods also have some problems: (1) the existing reinforcement methods do not include the content and design method of out-of-plane reinforcement of brick masonry walls. (2) There is no specific calculation method for the out-of-plane bending bearing capacity of brick masonry walls. The existing reinforcement methods are only based on experience, lack of reliable theoretical basis, and have low safety factor. (3) The size of the wall is increased, the net area of the room in the building is reduced, the wall load is greatly changed compared with the original wall, and the original force system and bearing structure are seriously affected. (4) The construction is complicated, a large amount of wet work is needed, the construction period is long, the noise is large, and the environmental pollution is serious. Therefore, it is necessary to provide a new out-of-plane reinforcement design method for brick masonry walls to solve the above problems. SUMMARY

[0005] The application aims to provide a design method for the out-of-plane flexural capacity of a brick masonry wall reinforced by externally bonded GFRP vertical strips, which utilizes the excellent strength and deformation capacity of GFRP, improves the poor integrity and insufficient out-of-plane flexural capacity of the brick masonry wall, effectively improves the out-of-plane flexural capacity and overall seismic performance of the brick masonry wall, avoids wet work during the reinforcement of the wall body, achieves the purpose of rapid and convenient construction, and saves operation space.

[0006] To achieve the above-mentioned purpose, the application provides a design method for the out-of-plane flexural capacity of a brick masonry wall reinforced by externally bonded GFRP vertical strips,

[0007] The structure of the brick masonry wall reinforced by externally bonded GFRP vertical strips comprises a brick masonry wall, GFRP vertical reinforcement strips, GFRP transverse anchoring strips and GFRP anchors; the GFRP vertical reinforcement strips are bonded on both sides of the brick masonry wall by using epoxy resin, the GFRP anchors are arranged in the bonding area of the GFRP vertical reinforcement strips, the GFRP transverse anchoring strips are arranged outside the GFRP vertical reinforcement strips and are bonded on the top, middle and bottom of the brick masonry wall by using epoxy resin, and the GFRP vertical reinforcement strips are anchored by the GFRP transverse anchoring strips and the GFRP anchors embedded in the brick masonry wall.

[0008] The design method for the out-of-plane flexural capacity comprises the following steps:

[0009] S1: determining the design values of the vertical load and the out-of-plane bending moment borne by the brick masonry wall;

[0010] S2: calculating the GFRP area of the brick masonry wall reinforced by externally bonded GFRP vertical strips according to the out-of-plane flexural capacity formula;

[0011] S3: checking the GFRP reinforcement rate, so that the GFRP reinforcement rate is not less than the minimum reinforcement rate and not more than the maximum reinforcement rate;

[0012] S4: determining the number of GFRP vertical reinforcement strips, the thickness and width of a single GFRP vertical reinforcement strip according to the GFRP area.

[0013] Preferably, in the step S2, the out-of-plane flexural capacity of the brick masonry wall reinforced by externally bonded GFRP vertical strips is calculated as follows:

[0014]

[0015]

[0016] σ = 0.75 (ε cu E f A f -N) / f cm b

[0017] η = 0.75N / f cm b

[0018] N = N t +N w

[0019] ε fd = ε cu (h-x) / x

[0020] In the formula, M u is the design value of the out-of-plane bending moment of the brick masonry wall reinforced by externally bonded GFRP vertical strips;

[0021] f cm is the design value of the compressive strength of the brick masonry wall;

[0022] b and h are the width and thickness of the brick masonry wall, respectively;

[0023] A f is the area of the GFRP strip on one side of the brick masonry wall;

[0024] ρ f is the GFRP reinforcement ratio;

[0025] x is the depth of the neutral axis;

[0026] E f is the elastic modulus of the GFRP strip;

[0027] N t is the vertical load on the brick masonry wall;

[0028] N w is the self-weight of the brick masonry wall;

[0029] ε fd is the strain of the GFRP strip when it is peeled off from the brick masonry wall;

[0030] ε cu is the ultimate compressive strain of the masonry, which is recommended to be 0.0034.

[0031] Preferably, in the step S3, when checking the GFRP reinforcement ratio, the GFRP reinforcement ratio ρ f should not exceed the maximum reinforcement ratio ρ f,max and should not be less than the minimum reinforcement ratio ρ f,min :

[0032] GFRP reinforcement ratio calculation:

[0033] ρ f = A f / bh

[0034] ρ f,min = 0.3fcm / f frp

[0035] ρ f,max =0.67ξ b f cm / f frp

[0036] ξ b =0.75ε cu / (ε cu +ε fd )

[0037] In the formula, ρ f,min , ρ f,max are minimum reinforcement rate and maximum reinforcement rate of GFRP respectively; f frp is ultimate tensile strength of GFRP strip.

[0038] Preferably, the GFRP vertical reinforcement strips are multiple and arranged at equal intervals.

[0039] Preferably, the GFRP horizontal anchoring strip width is the same as the GFRP vertical reinforcement strip width.

[0040] Preferably, three GFRP horizontal anchoring strips are used.

[0041] Preferably, each GFRP vertical reinforcement strip is provided with 5 GFRP anchors arranged at equal intervals.

[0042] Preferably, the GFRP anchor is 100mm long and 8mm in diameter, and the hole for installing the GFRP anchor is 12mm in diameter and 50mm in depth.

[0043] The design idea of the application is that GFRP strips are pasted on the wall surface to form a force whole with the wall, resisting out-of-plane load together. When calculating the out-of-plane flexural capacity of brick masonry wall, the out-of-plane bending process of brick masonry wall is equivalent to the bending process of a simply supported reinforced concrete beam, and the following assumptions are followed in the cross-section stress analysis: (1) the wall section still maintains a plane during the bending process, and the in-plane stress and strain are linearly distributed; (2) the tensile strength of brick masonry is not considered, that is, the tensile stress is completely borne by the GFRP strip; (3) the masonry compression constitutive curve is a parabola, and the ultimate compression strain of masonry is 0.0034.

[0044] Compared with the prior art, the application has the advantages that (1) a specific formula for calculating the out-of-plane flexural capacity of the GFRP reinforced brick masonry wall is provided, which can significantly improve the out-of-plane flexural capacity of the wall and has reliable theoretical basis and sufficient safety reserve; (2) compared with the traditional steel plate and steel wire mesh reinforcement, the GFRP strip has the characteristics of high strength and corrosion resistance, and has a long service life; (3) the application adopts the GFRP strip to reinforce the brick masonry wall, and only the GFRP strip is pasted on the two side surfaces of the wall, which almost does not increase the size and load of the wall and has little influence on the original building area and structural self-weight; (4) the GFRP strip applied in the application can be directly cut and processed in the factory, the construction process is simple and convenient, the wet operation amount is small, the construction period can be greatly shortened, and the cost can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a perspective view of the brick masonry wall structure reinforced by the application of the GFRP strip;

[0046] Figure 2 is Figure 1 A-A sectional view in the figure;

[0047] The reference signs are explained as follows: 1-GFRP vertical reinforcing strip; 2-GFRP transverse anchoring strip; 3-GFRP anchor bolt; 4-brick masonry wall. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the application more clear and explicit, the application is further described in detail below in combination with the drawings and examples.

[0049] Example:

[0050] A brick masonry wall made of sintered clay bricks has a width b, a height z and a thickness h of 1500 mm, 1800 mm and 240 mm respectively, the masonry compressive strength f cm is 3.21 MPa, the vertical load on the top of the wall is 250 kN, and the out-of-plane bending moment design value is 29.7 kN·m. The GFRP strip is used for reinforcement, the GFRP elastic modulus E f is 20900 N / mm 2 , and the tensile strength f frp is 460 N / mm 2 .

[0051] The design method of the out-of-plane flexural capacity of the brick masonry wall reinforced by the external GFRP vertical strip is as follows:

[0052] 1. Determine the vertical load and the out-of-plane bending moment design value of the brick masonry wall.

[0053] The out-of-plane bending moment design value Mu = 29.7 x 106N mm;

[0054] Vertical load on brick wall N w = 250 kN

[0055] Self weight of brick wall N t = 19 x 1500 x 1800 x 240 = 12.312 kN;

[0056] 2. Calculate the area of GFRP strip on one side of the brick wall according to the formula of out-of-plane flexural capacity.

[0057] Out-of-plane flexural capacity of brick wall strengthened with externally bonded GFRP vertical strips:

[0058]

[0059]

[0060] σ = 0.75 (ε cu E f A f -N) / f cm b

[0061] η = 0.75 N / f cm b

[0062] N = N t +N w

[0063] ε fd = ε cu (h-x) / x

[0064] 29.7 x 106≤ 0.67 x 3.21 x 1500 x 0.75 x x x 240 / 2 - 0.375 x + A f x 20900 x ε fd x 240 / 2

[0065]

[0066] σ = 0.75 x (0.0034 x 20900 A f -N) / 3.21 x 1500

[0067] η = 0.75 N / 3.21 x 1500

[0068] N = 12.312 + 250 = 262.312 kN

[0069] A f = 780.0 mm2;

[0070] 3, GFRP strip reinforcement rate review, GFRP reinforcement rate is not more than the maximum reinforcement rate and not less than the minimum reinforcement rate;

[0071] ρ f = A f / bh = 780 / 1500 x 240 = 0.0022

[0072] ρ f,min = 0.3f cm / f frp = 0.3 x 3.21 / 460 = 0.0021

[0073]

[0074] ε fd = ε cu (h-x) / x = 0.0034 x (240-178.39) / 178.39 = 0.0012

[0075] ξ b = 0.75 ε cu / ( ε cu + ε fd ) = 0.75 x 0.0034 / (0.0034+0.0012) = 0.55

[0076] ρ f,max = 0.67 ξ b f cm / f frp = 0.67 x 0.55 x 3.21 / 460 = 0.0026

[0077] ρ f,min ≤ ρ f ≤ ρ f,max , GFRP reinforcement rate meets the requirements.

[0078] 4, determine the number and width of GFRP strip.

[0079] The number of GFRP strip is selected as 4, the area of single GFRP strip is A f / 4 = 780 / 4 = 195mm 2

[0080] The thickness of GFRP strip is selected as 1.3mm

[0081] The width of GFRP strip a = 195 / 1.3 = 150.0mm.

[0082] The construction method of the outer GFRP reinforced brick masonry wall structure is as follows:

[0083] (1) The surface of the brick masonry wall is polished.

[0084] Before the reinforcement construction, a clean and smooth sticking work surface is needed. The polishing area is determined by the position of sticking, and the wall surface is polished until the brick interior can be seen. For the protruding parts on the test piece, polish until the new surface is exposed and smooth. After polishing, use the air blower and high-pressure water gun to clean it.

[0085] (2) Bottom coating of epoxy resin.

[0086] In the reinforced area, apply polymer textile reinforced mortar leveling. After the reinforced mortar leveling layer is completely cured, evenly apply the prepared epoxy resin to the sticking position.

[0087] (3) Masonry structure surface repair and leveling.

[0088] In order to make the GFRP strip fully play its role, the surface of the structure to be pasted should be kept smooth, so it is necessary to repair and level the surface before sticking. Use leveling mortar to level the uneven areas on the wall surface.

[0089] (4) Sticking of GFRP fiber strips.

[0090] Cut the GFRP strip to the designed size with a ruler and a craft knife. First, stick the GFRP vertical reinforcement strip. When sticking, slowly roll the GFRP strip from top to bottom, and make sure the water level is uniform during construction. After sticking the GFRP vertical reinforcement strip, stick the same width of GFRP horizontal anchoring strip at the top, middle and bottom of the brick wall as anchoring. After all the sticking is completed, use a scraper and a roller to repeatedly press and roll to completely extrude the air bubbles inside the GFRP, preventing stress concentration.

[0091] (5) Installation of anchors.

[0092] The GFRP anchor is 100mm long and 8mm in diameter. It is made of glass fiber bundles extracted from glass fiber cloth. First, determine 5 equally spaced GFRP anchor installation positions on each GFRP vertical reinforcement strip. Then, use an impact drill to drill a hole with a diameter of 12mm and a depth of 50mm at the installation position, fill the hole with epoxy resin, and then insert the GFRP anchor. Finally, evenly spread the remaining 50mm long GFRP anchor into a ring shape, and evenly apply epoxy resin on the surface of the anchor. After installation, slowly roll to remove the air bubbles remaining in the fiber.

[0093] (6) Wall maintenance.

[0094] From the moment of construction completion, the GFRP reinforced brick wall structure needs to be maintained in the natural environment for 7 days. After the epoxy resin is completely cured, the GFRP strip can play its reinforcing effect.

[0095] It should be noted that modifications and improvements can be made by those skilled in the art, which modifications and improvements are also within the scope of the present application without departing from its spirit.

Claims

1. A method for designing the out-of-plane flexural capacity of a brick masonry wall externally reinforced with GFRP vertical strips, characterized in that: the structure of the brick masonry wall externally reinforced with GFRP vertical strips comprises a brick masonry wall, GFRP vertical reinforcement strips, GFRP transverse anchorage strips and GFRP anchors; the GFRP vertical reinforcement strips are adhered to both sides of the brick masonry wall using epoxy resin, the GFRP anchors are arranged in the area where the GFRP vertical reinforcement strips are adhered, and the GFRP transverse anchorage strips are arranged outside the GFRP vertical reinforcement strips and adhered to the top, middle and bottom of the brick masonry wall using epoxy resin, respectively; the GFRP vertical reinforcement strips are anchored by the GFRP transverse anchorage strips and the GFRP anchors embedded in the brick masonry wall; the method for designing the out-of-plane flexural capacity comprises the following steps: S1: determining the design values of the vertical load and the out-of-plane bending moment acting on the brick masonry wall; S2: calculating the GFRP area of the brick masonry wall externally reinforced with GFRP vertical strips according to the out-of-plane flexural capacity formula; S3: checking the GFRP reinforcement ratio to ensure that the GFRP reinforcement ratio is not less than the minimum reinforcement ratio and not more than the maximum reinforcement ratio; S4: determining the number of GFRP vertical reinforcement strips, the thickness and width of a single GFRP vertical reinforcement strip according to the GFRP area; in step S2, the out-of-plane flexural capacity of the brick masonry wall externally reinforced with GFRP vertical strips is calculated as follows: wherein b and h are the width and thickness of the brick masonry wall, respectively; x is the depth of the neutral axis; and GFRP is the GFRP area. The GFRP reinforcement ratio is calculated as follows: σ = 0.75 (ε cu E f A f -N) / f cm b η = 0.75 N / f cm b N = N t + N w ε fd = ε cu (h - x) / x In the formula, M u is the design value of the out-of-plane bending moment of the brick masonry wall reinforced by externally bonded GFRP vertical strips. f cm f cm f cm f cm f cm f cm f The GFRP vertical reinforcement strips are multiple and arranged at equal intervals. A f GFRP strip area for one side of brick wall; The width of the GFRP transverse anchorage strip is the same as that of the GFRP vertical reinforcement strip. E f E for GFRP strip modulus of elasticity; N t The vertical load received by the brick wall; N w For brick masonry walls self-weight; epsilon fd is the strain at which the GFRP strip is stripped from the brick masonry wall; ε cu εlimis the ultimate compressive strain of the masonry.

2. The design method of the out-of-plane flexural capacity of brick masonry walls externally reinforced with GFRP vertical strips according to claim 1, characterized in that: In the step S3, when checking the GFRP reinforcement ratio, the GFRP reinforcement ratio p f is not more than the maximum reinforcement ratio p f,max and is not less than the minimum reinforcement ratio p f,min : The GFRP transverse anchorage strip is three. ρ f = A f / bh p f,min = 0.3f cm f frp p f,max = 0.67ξ b f cm f frp ξ b = 0.75 ε cu / ( ε cu + ε fd ) wherein ρ f,min , ρ f,max are the minimum and maximum reinforcement rates of GFRP, respectively; f frp is the ultimate tensile strength of the GFRP strip.

3. The method according to claim 1, wherein the method is characterized in that: Each GFRP vertical reinforcement strip is provided with five GFRP anchors arranged at equal intervals.

4. The design method of the out-of-plane flexural capacity of brick masonry walls externally bonded with GFRP vertical strips according to claim 3, characterized in that: The GFRP anchor is 100 mm long and 8 mm in diameter, and the hole for installing the GFRP anchor is 12 mm in diameter and 50 mm in depth.

5. The design method of the out-of-plane flexural capacity of brick masonry walls externally reinforced with GFRP vertical strips according to claim 4, characterized in that: ​ 6. The design method of the out-of-plane flexural capacity of brick masonry walls externally reinforced with GFRP vertical strips according to claim 5, characterized in that: ​ 7. The design method of the out-of-plane flexural capacity of brick masonry walls externally reinforced with GFRP vertical strips according to claim 6, characterized in that: ​

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