Structural behavior of FRP-strengthened reinforced concrete shear walls with openings using finite element method

Abstract

Reinforced concrete shear walls with features such as high stiffness, good performance in earthquakes, ductility, and high bearing capacity in earthquake-prone regions are widely used as convenient and reliable structural systems in medium- and high-rise reinforced concrete buildings. However, due to architectural limitations, the use of opening in shear walls is unavoidable. Fiber-reinforced polymer sheets with unique structural characteristics and easy implementation have been used in recent years for rehabilitating concrete structures, especially shear walls. In this study, using the finite element method, the effect of openings with different sizes and locations in reinforced concrete shear walls was studied. The effect of retrofitting specimens with openings by carbon fiber–reinforced polymer sheets with different patterns and thicknesses on the structural behavior of shear walls was also investigated. According to the results, opening reduced the bearing capacity, energy absorption capacity, and stiffness but increased wall displacement. Different reinforcement patterns and different thicknesses of carbon fiber–reinforced polymer sheets had different effects on improved structural behavior of shear walls. Reinforcement with carbon fiber–reinforced polymer sheets is one of the effective ways to rehabilitate concrete shear walls with opening.

Keywords

bearing capacity carbon fiber–reinforced polymer sheets finite element opening reinforced concrete shear wall

Introduction

Reinforced concrete shear walls are a type of structural systems including concrete and steel bars with very high in-plane stiffness. They provide lateral strength of buildings or structures against lateral loads (shear forces and bending moments), especially earthquake loads. Reinforced concrete shear walls with suitable structural properties are considered as major members of medium- and high-rise reinforced concrete buildings against earthquake forces. With structural damages over the time, poor implementation and lack of proper implementation, changes in the geometry of walls such as opening and other factors, retrofitting and rehabilitating of the existing reinforced concrete buildings have received much attention. In the meantime, retrofitting reinforced concrete shear walls, as the main bearing members of the buildings, is essential. In this regard, various methods such as increasing cross-section and metal jacket for retrofitting reinforced concrete walls have been used. These methods are associated with drawbacks such as adding weight to the structure, disrupting building use during implementation and changes in lateral stiffness and load distribution in building. Due to the unique structural properties such as resistance to high weights, excellent resistance to corrosion, and easy implementation, fiber-reinforced polymer (FRP) sheets have been widely used in recent years for retrofitting reinforced concrete buildings. In particular, shear walls reinforced with FRP sheets are considered as a novel retrofitting method.

Ehsani and Saadatmanesh (1997) studied the use of FRP sheets for retrofitting the walls in concrete buildings remained from the Northridge earthquake. Lombard et al. (2000) studied reinforcing four shear walls with carbon fiber–reinforced polymer (CFRP) sheets and found that reinforcing damaged walls with CFRP sheets recovered initial stiffness and increased flexural capacity of the walls. The use of CFRP sheet in reinforcing healthy walls increased stiffness and lateral bearing capacity. Li and Lim (2010) carried out laboratory research on damaged concrete shear walls reinforced with FRP sheets. Their results showed that repair of damaged walls with FRP sheets may recover the original function of the wall.

Mostofinejad et al. (2012) studied reinforcement of cross-border elements of slender reinforced concrete shear walls with FRP coatings under uniform loads and its effect on the flexural behavior of the walls. The results showed that the use of FRP coating in border areas in plastic hinge zone of shear walls is a cost-effective and reasonable method for reinforcement of shear walls with poor design to deal with seismic loads. Since openings in shear walls have a great impact on their behavior, reinforcing and rehabilitating walls with openings is of great importance. Reinforcing such walls with new materials, especially with FRP sheets have received much attention. Hansen et al. (2009) carried out theoretical studies on shear walls with opening reinforced with FRP sheets. Their results showed that in shear walls with small openings, the development of a new yield mechanism outside the reinforced areas is a natural reasonable way causing flexible failure of the wall. Mohammed et al. (2013) studied different reinforcement methods for FRP-reinforced concrete shear walls with openings by testing 16 specimens with opening percentage of 5%, 10%, 20%, and 30%. It was found that the bearing capacity of the shear walls with openings was improved with CFRP reinforcement and consequently with reduction of active stresses in the upper corner of the opening. Behfarnia and Sayah (2012) conducted theoretical studies on the impact of openings in shear walls reinforced with FRP sheets. Their results showed that the CFRP sheets caused maximum reinforcement in shear walls with opening with an area of 25% (relative to the total area of the wall) associated with 39% increase in capacity. Lima et al. (2014) conducted laboratory research on the reinforcement effect around openings in shear walls reinforced with CFRP sheets. Their results showed that in most cases, the use of CFRP in opening corners gives better results than their use with an angle of 45° in opening corners. Todut et al. (2015) conducted an experimental and numerical study on prefabricated reinforced concrete wall panels reinforced with FRP composite sheets with seismic damage. The experimental results showed that the performance of repaired and reinforced elements was equal and better than the reference element in terms of load capacity, stiffness, and energy absorption capacity. The reinforced elements also showed more ductile behavior.

In this study, a concrete shear wall was modeled with the help of the finite element software, ABAQUS. The comprehensive investigation about the effect of openings with different sizes in the center and bottom of the wall on structural behavior using nonlinear static pushover analysis has done. Then, the specimens with openings were reinforced with three different patterns using CFRP sheets with three thicknesses of 0.09, 0.18, and 0.27 mm. The effect of different reinforcement patterns and thicknesses of CFRP sheets on the lateral bearing capacity, displacement, energy absorption capacity, and elastic stiffness as well as tensile and compressive damages in the concrete walls were studied. Suitable reinforcement pattern for each shear wall with opening, the impact of different patterns on increasing ultimate bearing capacity, energy absorption capacity and elastic stiffness of the specimens, and reducing wall displacement as well as economic factors such as the surface area of CFRP sheets used in each pattern and ease-of-implementation of reinforcement pattern were investigated.

Validation of numerical analysis

To verify the results obtained from ABAQUS/CAE, a shear wall studied by Altin et al. (2013) was selected. The shear wall with a scale of 1/2 relative to the actual wall was constructed in the laboratory with dimensions of 1000×1500×10 mm. For this purpose, concrete with a 28-day compressive strength of 15.5 MPa was used with rebar with a yield stress of 325–430 MPa. Figure 1 shows details of reinforcement and loading of the experimental model.

Figure 1.

Details of reinforcement and loading of the experimental model (Altin et al., 2013).

Figure 2 shows the results of experimental and numerical modeling of the concrete wall in the form of drift–shear force chart. As shown in the figure, there is a good agreement between the numerical and experimental modeling. The ultimate load in the analytical and experimental models was 153 and 146 kN, respectively.

Figure 2.

The drift–shear force ratio in the experimental and analytical models.

Modeling

In this study, the concrete shear wall of the first floor of a building in Sanandaj city was selected as the base model. The residential building with six floors is constructed with an area of 271.10 m² in each floor. The height of the basement and ground floors was 2.8 m and the height of other floors was 3.20 m. The building was designed with a concrete structure with ceiling joists and blocks and a system of lateral bending frame with shear walls with an average ductility according to ACI-08 Regulation with the help of ETABS. The reference shear wall has dimensions of 2.20×2.80×0.3 m. Figure 3 shows the reinforcement details and wall dimensions. The CFRP sheets used in this study have bidirectional fibers with wrapping angles of 0° and 90°. The properties of the materials are described in Table 1.

Figure 3.

Details of reinforcement of the reference shear wall (dimensions in centimeter).

Table 1.

Properties of the materials used.

Property	Concrete	CFRP	Epoxy	Steel
Modulus of elasticity, E (GPa)	25	230	7	200
Yield strength, f_y (MPa)	–	–	–	400
Tensile strength, f_t (MPa)	3	3800	25	600
Compressive strength, $f'_{c}$ (MPa)	24	–	70	–
Poisson’s ratio	0.2	0.3	0.3	0.3
Thickness (mm)	–	0.09	–	–
Density (kN/m³)	24	17.5		78.5

In this study, nonlinear finite element analyses were performed with the help of ABAQUS. Concrete damage plasticity model as a powerful model to simulate the behavior of concrete was accepted. Kent–Park’s model was used to define concrete compressive behavior.

Kent and Park (1971) proposed stress–strain equations for both unconfined and confined concrete. In their model, they generalized Hognestad’s (1951) equation to more completely describe the post-peak stress–strain behavior. In this model, the ascending branch is represented by modifying the Hognestad second-degree parabola by replacing ${f ″}_{c}$ by $f'_{c}$ and $ε_{0}$ by 0.002

For 0 < ε_{c} < ε_{0} f_{c} = f'_{c} [(\frac{2 ε_{c}}{ε_{0}}) - {(\frac{ε_{c}}{ε_{0}})}^{2}]

where $ε_{c}$ is the uniaxial strain, $f'_{c}$ is the material strength, and $ε_{0} = 0.002$ , is the ultimate uniaxial strain associated with material strength.

The post-peak branch was assumed to be a straight line whose slope was defined primarily as a function of concrete strength

For ε_{0} < ε_{c} < ε_{u} f_{c} = f'_{c} (1 - Z (ε_{c} - ε_{0})) Z = (\frac{0.5}{ε_{50 u} - ε_{0}})

where $ε_{50 u}$ is the strains corresponding to the stress equal to 50% of the maximum concrete strength for unconfined concrete ( $ε_{50 u} = (3 + 0.29 f'_{c}) / (145 f'_{c} - 1000) (f'_{c} in MPa)$ ).

Furthermore, Nayal and Rashid’s model was used to define concrete tensile behavior (see Figure 4).

Figure 4.

Tension stiffening model (Nayal and Rasheed, 2006).

Two linear models were used to model the tensile and compressive behavior of steel. Solid C3D8R element was used to create a three-dimensional model of the concrete. Trust T3D2 model was used for three-dimensional modeling of reinforcement. Shell S4R element was also used for modeling CFRP sheets. Embedded region interaction implemented to define the contact between the concrete and reinforcement. The Tie constraint was used for contact between concrete and CFRP sheets.

To investigate the effect of opening, nine shear walls with the following characteristics were modeled in the finite element software, ABAQUS. The walls were loaded with nonlinear static pushover analysis with a displacement equivalent to 2% of the wall height (0.056 m) to the top of the wall.

The specimen without opening abbreviated Reference Wall (RW).

The specimens with a 0.5×0.5 m, 0.8×0.8 m, and 1.1×1.1 m square opening at the center of the wall abbreviated RW C50C, RW C80C, and RW C110C, respectively.

The specimens with a 0.5×0.5 m, 0.8×0.8 m, and 1.1×1.1 m square opening at the bottom of the wall abbreviated RW C50B, RW C80B, and RW C110B, respectively.

The specimens with a 0.8×2.00 and 1.10×2.00 rectangular opening at the bottom of the wall abbreviated RW C80200B and RW C110200B, respectively.

To investigate the effect of reinforcement patterns, the shear walls with openings were reinforced with three different patterns:

Reinforcement with strips of CFRP sheet with a width of the half of the opening length with an angle of 45° at the corners of the opening on both sides of the wall.

Reinforcing the opening round with strips of CFRP sheet with a width of the half of the opening length on both sides of the wall.

Reinforcing the abutments while reinforcing the wall at the top and bottom of the opening to the height of the half of opening length by wrapping CFRP sheets.

The specimens with square openings were modeled with three reinforcement patterns. The specimens with rectangular openings were modeled and analyzed with the reinforcement patterns 2 and 3. To investigate the effect of thickness of CFRP sheets, all reinforced specimens were studied with the CFRP layer with a fiber thickness of 0.09, 0.18, and 0.27 mm.

The reinforced specimens were loaded with nonlinear static pushover analysis through displacement equal to 2% of the height of the wall to the top of the wall. A total of 66 reinforced specimens were analyzed. Figure 5 shows reinforcement patterns for specimens with a central opening. Figure 6 shows reinforcement patterns for specimens with opening at anchor.

Figure 5.

Reinforcement patterns of specimens with a central opening for three reinforced specimens.

Figure 6.

Reinforcement patterns of specimens with an opening at anchor for three reinforced specimens.

To designate the specimens reinforced with CFRP sheets, the letter R in the abbreviated name of the unreinforced specimen is changed to the letter S. To show the reinforcement pattern and thickness (number of layers) of CFRP sheet, three letters are used at the end of specimen code. Each of these letters indicates the following: The first letter stands for pattern (reinforcement pattern with CFRP sheet). The second letter is 1, 2, or 3, respectively, showing patterns 1, 2, or 3. The third letter is 1, 2, or 3 which represents the number of reinforcement layers (thickness).

Results

Figure 7 shows the force–displacement curves for the specimen without opening and those with openings at the center of wall and at anchor.

Figure 7.

The force–displacement curves for the specimens without opening and those with openings at the center and anchor.

Table 2 shows the values of the reference specimen (without opening) and specimens with openings at the center and anchor in terms of ultimate lateral bearing capacity, energy absorption capacity, and elastic stiffness of wall.

Table 2.

Values of the reference specimen and those with openings at the center and anchor.

Specimen	Ultimate lateral bearing capacity (kN)	Energy absorption capacity (kN mm)	Elastic stiffness (kN/mm)
RW	839.42	44,122	484.01
RW C50C	803.667	41,400.9	448.69
RW C80C	663.43	33,797.8	350.01
RW C110C	464.27	22,752.3	215.02
RW C50B	684.72	36,257.4	429.38
RW C80B	574.13	30,076.1	351.97
RW C110B	468.35	24,189.2	228.7
RW C80200B	469.24	23,557.51	196.45
RW C110200B	305.31	15,185.5	125.07

Table 3 compares the reference specimen (without opening) and specimens with openings at the center and anchor in terms of ultimate lateral bearing capacity, energy absorption capacity, and elastic stiffness of wall.

Table 3.

Comparison of the reference specimen and those with openings at the center and anchor.

Specimen	Ultimate lateral bearing capacity reduction	Energy absorption capacity reduction	Elastic stiffness reduction
RW C50C	4.26	6.17	7.30
RW C80C	20.97	23.40	27.69
RW C110C	44.69	48.43	55.58
RW C50B	18.43	17.83	11.29
RW C80B	31.60	31.83	27.28
RW C110B	44.21	45.18	52.75
RW C80200B	44.10	46.61	59.41
RW C110200B	63.63	65.58	74.16

As shown in Figure 7 and Table 3, the ultimate lateral bearing capacity, energy absorption capacity, and elastic stiffness of the wall decrease while displacement increases with increasing the size of openings at the center or anchor. The amount of increase or decrease is different depending on the opening location or dimensions. According to the results in Table 1, the 0.5×0.5 opening has a little effect on reducing the lateral bearing capacity and energy absorption capacity of the wall while changing the location of the opening of the same dimensions to the wall bottom, significantly reduced the ultimate lateral bearing capacity and energy absorption capacity of the wall due to interrupted path of load transfer to the anchor. Figures 8 and 9 show tensile and compressive damages of the concrete at the end of loading for the specimen without opening and for some specimens with opening.

Figure 8.

Tensile damage of the concrete at the end of loading for the specimens: (a) without opening, (b) with 1.1 × 1.1 m opening at the center, (c) 0.8 × 0.8 m opening at anchor, and (d) 1.1 × 2 m opening at anchor.

Figure 9.

Compressive damage of the concrete at the end of loading for the specimens: (a) without opening, (b) with 1.1 × 1.1 m opening at the center, (c) 0.8 × 0.8 m opening at anchor, and (d) 1.1 × 2 m opening at anchor.

As seen in Figures 8 and 9, the openings in the shear walls change the tensile and compressive damage patterns of the concrete. Given the reduction of bearing capacity of the specimens with opening, the tensile damage is less than the specimen without opening. The openings also change the location and severity of compressive damage to the concrete. Figure 10 and Table 4 show the results of analysis for the specimens with openings at the center and anchor reinforced with pattern 1 using CFRP sheets with three different thicknesses.

Figure 10.

The force–displacement curves of specimens with opening strengthened using pattern 3.

Table 4.

Percentage increase in the structural behaviors of specimens with openings reinforced with CFRP sheets using pattern 1 compared to the unreinforced specimen with opening.

Specimen	Increased ultimate lateral bearing capacity	Increased energy absorption capacity	Increased elastic stiffness
SW C50C P11	3.83	2.39	2.45
SW C50C P12	4.06	3.02	2.49
SW C50C P13	3.86	2.86	2.53
SW C80C P11	18.36	12.74	5.38
SW C80C P12	19.48	15.04	5.63
SW C80C P13	19.68	16.03	5.83
SW C110C P11	14.61	12.19	2.99
SW C110C P12	17.08	15.34	3.32
SW C110C P13	19.37	16.82	3.62
SW C50B P11	3.82	3.03	3.09
SW C50B P12	3.32	3.00	3.12
SW C50B P13	2.97	2.77	4.18
SW C80B P11	0.67	1.36	3.85
SW C80B P12	1.55	1.16	4.050
SW C80B P13	1.79	2.07	4.64
SW C110B P11	0.47	0.67	7.34
SW C110B P12	0.42	0.80	7.54
SW C110B P13	0.40	1.17	7.72

As seen in Figure 10 and Table 4, the reinforcement pattern 1 is suitable to reinforce specimens with a small opening at the center of the wall. This pattern has a very little impact on increasing the ultimate bearing capacity, energy absorption capacity, and elastic stiffness of specimens with opening at anchor and does not work for reinforcing such specimens. In this reinforcement pattern, increasing the thickness of CFRP sheets has a little impact on increasing the ultimate bearing capacity, energy absorption capacity, and elastic stiffness. Figure 11 and Table 5 show the results of analysis for the specimens with openings at the center and anchor reinforced with pattern 2 using CFRP sheets with three different thicknesses.

Figure 11.

The force–displacement curves of specimens with opening strengthened using pattern 2.

Table 5.

Percentage increase in structural behaviors of specimens with openings strengthened with CFRP sheets of different thicknesses with pattern 2 compared to the unreinforced specimen with opening.

Specimen	Increased ultimate lateral bearing capacity	Increased energy absorption capacity	Increased elastic stiffness
SW C50C P21	4.19	2.82	2.42
SW C50C P22	3.30	4.02	2.50
SW C50C P23	4.62	4.40	2.58
SW C80C P21	24.97	17.83	4.77
SW C80C P22	32.16	23.99	5.28
SW C80C P23	33.16	26.56	5.75
SW C110C P21	49.91	33.55	5.31
SW C110C P22	70.39	49.36	6.31
SW C110C P23	79.08	59.60	7.03
SW C50B P21	6.30	1.56	−3.30
SW C50B P22	9.10	2.64	−3.02
SW C50B P23	11.52	3.32	−3.64
SW C80B P21	16.96	7.79	−8.86
SW C80B P22	27.18	15.42	−8.85
SW C80B P23	30.95	19.71	−8.85
SW C110B P21	10.35	3.87	−9.66
SW C110B P22	13.90	8.35	−9.62
SW C110B P23	19.04	11.62	−11.95
SW C80200B P21	22.66	16.39	3.30
SW C80200B P22	39.81	25.05	2.08
SW C80200B P23	53.03	33.88	4.68
SW C110200B P21	46.38	27.83	5.80
SW C110200B P22	75.94	46.72	6.54
SW C110200B P23	102.70	63.41	6.84

As seen in Figure 11 and Table 5, the reinforcement pattern 2 increases the bearing capacity, energy absorption capacity, elastic stiffness while reducing displacement in specimens with central openings and those with rectangular openings at anchor. In this reinforcement pattern, increasing the thickness of CFRP sheets has different effects on the behavior of specimens depending on the size and location of openings leading to an increase in the ultimate bearing capacity, energy absorption capacity and a decrease in the displacement. In most cases, it increases the elastic stiffness of specimens. The greatest impact of the reinforcement pattern in increasing bearing capacity and energy absorption capacity was found in the specimen with a 1.1×2.0 opening at anchor reinforced with three CFRP layers.

Figure 12 and Table 6 show the results of analysis for the specimens with openings at the center and anchor reinforced with pattern 3 using CFRP sheets with three different thicknesses.

Figure 12.

The force–displacement curves of specimens with opening strengthened using pattern 3.

Table 6.

Percentage increase in structural behaviors of specimens with openings strengthened with CFRP sheets using pattern 3, compared to the unreinforced specimen with opening.

Specimen	Increased ultimate lateral bearing capacity	Increased energy absorption capacity	Increased elastic stiffness
SW C50C P31	4.78	4.24	2.56
SW C50C P32	4.75	4.76	2.75
SW C50C P33	4.83	5.08	3.52
SW C80C P31	26.96	19.50	5.28
SW C80C P32	28.45	24.30	6.27
SW C80C P33	29.29	26.49	7.13
SW C110C P31	36.08	28.62	6.90
SW C110C P32	52.39	42.16	8.41
SW C110C P33	62.88	52.10	9.85
SW C50B P31	41.43	27.25	5.57
SW C50B P32	51.86	35.54	7.33
SW C50B P33	56.55	41.65	8.69
SW C80B P31	61.84	39.71	6.35
SW C80B P32	84.08	57.71	5.59
SW C80B P33	99.85	69.20	10.77
SW C110B P31	76.38	46.73	10.27
SW C110B P32	120.76	76.45	10.60
SW C110B P33	150.35	99.20	15.30
SW C80200B P31	58.94	34.25	3.45
SW C80200B P32	103.13	61.46	5.35
SW C80200B P33	140.66	84.13	8.81
SW C110200B P31	71.49	42.89	5.24
SW C110200B P32	118.67	73.40	7.19
SW C110200B P33	163.91	99.42	9.02

As shown in Figure 12 and Table 6, the reinforcement pattern 3 is suitable to reinforce the specimens with central openings and those with an opening at anchor. But it has a significant impact on increasing bearing capacity, energy absorption capacity, and elastic stiffness as well as reducing displacement in specimens with openings at anchor. This is due to the continued reinforcement of CFRP sheets to the wall anchor and prevention of wall failure at anchor. In this reinforcement pattern, increasing the thickness of CFRP sheets has different effects on the behavior of specimens depending on the size and location of openings leading to an increase in the ultimate bearing capacity, energy absorption capacity and a decrease in the displacement. In most cases, it increases the elastic stiffness of the specimens.

Figure 13 shows tensile damage of the concrete at the end of loading in the specimens with 0.8×0.8 m openings at the center without reinforcement and those reinforced with 0.18-mm-thick CFRP sheets with different patterns. Figure 14 shows compressive damage of the concrete in the specimens with 0.8×2 m openings at anchor without reinforcement and those reinforced with 0.27-mm-thick CFRP sheets with different patterns at the end of loading.

Figure 13.

Tensile damage of the concrete in the specimens with 1.1 × 1.1 m openings: (a) without reinforcement, (b) 0.18-mm- thick CFRP sheets with pattern 1, (c) 0.18-mm-thick CFRP sheets with pattern 2, and (d) 0.18-mm-thick CFRP sheets with pattern 3.

Figure 14.

Compressive damage of the concrete in the specimens with 0.8 × 2 m openings: (a) without strengthening, (b) with 0.27-mm-thick CFRP sheets with pattern 2, and (c) with 0.27-mm-thick CFRP sheets with pattern 3.

As shown in Figures 13 and 14, reinforcement of specimens with opening by CFRP sheets changes the tensile and compressive concrete damage patterns. According to the type of reinforcement as well as thickness of CFRP sheets, the tensile and compressive damages in the reinforced concrete specimens change compared to the unreinforced specimens.

Conclusion

In this research work, the effect of openings in the concrete shear wall and reinforcement of specimens with opening using CFRP sheets with three thicknesses of 0.09, 0.18, and 0.27 mm with three different reinforcement patterns were investigated. For this purpose, different concrete shear walls were modeled and analyzed in the finite element software, ABAQUS. The results obtained from FEM analysis were compared. The following results were obtained:

Openings in the shear walls reduced the lateral bearing capacity, energy absorption capacity, and stiffness while increasing wall displacement. The lateral bearing capacity, energy absorption capacity, and stiffness decreased while wall displacement increased with increasing the size of the opening.

A small 50×50 cm opening (opening length equals 22.73% of the wall length) at the center of the wall reduced the ultimate bearing capacity of the wall by 4.26%. With shifting the opening of the same size to the wall anchor, the ultimate bearing capacity of the wall decreased 18.43% due to interruption of the path to transfer load to the anchor. The same is true for the energy absorption capacity of the wall. In specimens with 1.1×1.1 openings (opening length is 50% of the wall length), the opening at the center or at anchor reduced the ultimate bearing capacity and energy absorption capacity of the wall almost at a same rate.

The tensile and compressive concrete damages in the reference specimen and those with opening showed that once the force is applied to the wall, the concrete first experiences a tensile damage. With increasing the load, tensile failure spreads in most parts of the wall. However, compressive damage to the concrete is very low and is limited to the corner of the wall at foundation at the far edge of the lateral force. The concrete undergoes compressive failure under high loads. Openings in the wall will change the pattern of development and spread of the tensile and compressive failure in the concrete. By increasing the size of the opening, tensile damage in the wall decreases due to the reduction in the ultimate bearing capacity.

Reinforcing the shear wall with opening using CFRP sheets increased bearing capacity, energy absorption capacity and reduced wall displacement. In most cases, it increased the elastic stiffness of the wall.

The effect of different reinforcement patterns on improved behavior of specimens with openings at center and anchor showed that the reinforcemnet patterns (1) and (2) have a greater impact on improved behavior of specimens with central openings. The reinforcement pattern (3) was effective in improving the behavior of the specimen with the opening at anchor.

Increasing the number of layers of reinforcement increased the ultimate bearing capacity, energy absorption capacity, and decreased wall displacement. In most cases, the elastic stiffness of the specimens increased. Depending on the size and location of openings as well as the pattern of reinforcement, it had different effects on ultimate bearing capacity, energy absorption capacity, and elastic stiffness.

To select the reinforcement pattern suitable for each shear wall with opening, the impact of different patterns on increasing ultimate bearing capacity, energy absorption capacity, and elastic stiffness of the specimens and reducing wall displacement as well as economic factors such as the surface area of CFRP sheets used in each pattern and ease-of-implementation of reinforcement pattern were investigated. It can be concluded that a specific reinforcement pattern is appropriate for each specimen. In the specimen with a 0.5×0.5 m opening at the center of wall, pattern 1 is appropriate. This pattern is not very useful for other type with large size of opening. In other words, when the size of opening is small such as 0.5×0.5 m, pattern 1 has the same effect to increase structural behavior of shear wall with opening, while it uses less CFRP sheets compare to patterns 2 and 3. The reinforcement pattern 2 is suitable for specimens with large opening at the center such as 0.8×0.80 m and 1.1×1.1 m openings at the center of wall. The reinforcement pattern 3 is suitable for the specimens at the anchor such as 0.5×0.5 m, 1.1×1.1 m, and 0.8×2 m and 1.1×2 openings at anchor.

Analysis of tensile and compressive damages of the reinforced concrete specimens indicated that reinforcement with CFRP sheets will change the pattern of tensile and compressive damages in the concrete. Given the role of CFRP sheets in load bearing after wall failure, tensile and compressive damages in the concrete were observed under higher loads compared to the unreinforced specimen. But given an increase in the ultimate bearing capacity in most reinforced specimens at the end of loading, the tensile and compressive concrete damages were more than in unreinforced specimens.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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