This paper presents the shear capacities of concrete beams reinforced with glass fiber reinforced polymer (GFRP) plates as shear reinforcement. To examine the shear performance, we manufactured and tested a total of eight specimens. Test variables included the GFRP stripwidthtospacing ratio and type of opening array. The specimen with a GFRP plate with a
Several studies have been carried out on the flexural behavior of concrete beams with fiber reinforced polymer (FRP) tensile reinforcement because FRP materials have advantages such as corrosion resistance, light weight, machinability, workability, and high strength [
In this paper, considering economics and ease of fabrication, we use a lattice shaped GFRP material for shear reinforcement. To evaluate the applicability of FRP plates for shear reinforcement, shear tests were conducted using concrete beams embedded with GFRP plates with openings, considering the array of the openings and the GFRP stripwidthtospacing ratio as the main variables. We also analyzed the failure modes and strain distributions.
Following ASTM C39 [
Schematic view of a concrete beam reinforced with GFRP plates.
We considered the array of openings, GFRP stripwidthtospacing ratio, and the amount of reinforcement as variables. The GFRP plates were manufactured in three shapes as shown in Figures
Details of the experimental variations of the GFRP plate designs.
Specimen  GFRP plate  

Type 

Width ( 
Thickness ( 
Centertocenter spacing of vertical strips ( 

(MPa)  (mm)  (mm)  (mm)  
A1  A  480  20  4  340 
A2  A  480  30  4  340 
A3  A  480  50  4  340 
A4  A  480  70  4  340 
A5  A  480  65  4  170 
A6  A  480  70  4  110 
B3  B  480  37.5  4  230 
C3  C  480  37.5  4  230 
Designs of the three experimental GFRP plates.
AType
BType
CType
Notation of geometry for a GFRP plate.
We tested a total of eight concrete beams embedded with GFRP plates with openings. Figure
Arrangement of GFRP plates in specimens.
A1
A2
A3
A4
A5
A6
B3
C3
Load was applied to each specimen at a rate of 5
Test setup of typical specimen.
Figure
Definitions of
Several mechanisms contribute to the shear capacities of reinforced concrete beams, such as the concrete, shear reinforcement, mechanical aggregates interlocking, and dowel action of the tensile reinforcement. Shear reinforcement has a mechanism for resistance to shear, as shown in Figure
Shear resistance by FRP shear reinforcement.
We assume the crack angle to be 45° when calculating the shear strength of the shear reinforcement. The tensile behavior of the FRP is characterized by a linearly elastic stressstrain relationship up to failure. Hence, shear failure is assumed to occur after fracture of the shear reinforcement.
As shown in (
ACI 440.1R provides a shear strength equation for concrete with FRP rebar flexural reinforcement. However, in this paper, we adopted the shear strength equation for concrete in ACI 318 because we used steel flexural reinforcement. The shear strength of the shear reinforcement can be calculated with (
As shown in Figure
Shearcompression failure in specimens.
A2
A3
B3
C3
We observed two typical failure modes in response to the amount of reinforcement provided. First, all the specimens except A5 and A6 fractured, and the plates ruptured after they had demonstrated their maximum shear strength. The concrete cover of specimens A5 and A6, on the other hand, fractured before the plate reached its maximum shear strength. The specimens showed two different failure modes because the size of the openings in the plates and the ratio of the area of the openings varied. This result could also be caused by a lack of concrete coverage. Therefore if the opening size, ratio of the area of openings, and sufficient concrete coverage conditions are met, the plate will demonstrate maximum shear strength, and the specimen will provide effective shear performance. The test results for maximum loading and maximum shear strength are summarized in Table
Maximum loading and shear strength test results.
Specimen 


Failure mode 

(kN)  (kN)  
A1  573.20  286.60  Shear 
A2  591.73  295.87  Shear 
A3  776.83  388.42  Shear 
A4  899.76  449.88  Shear 
A5  748.74  374.37  Shear 
A6  950.27  475.14  Shear 
B3  872.64  436.32  Shear 
C3  757.93  378.97  Shear 
Figure
Size and opening dimensions of FRP reinforcements.
Specimen 




Opening/FRP plate (%) 

A1  700  340  320  125  67.23 
A2  710  340  310  125  64.21 
A3  730  340  290  125  58.42 
A4  750  340  270  125  52.94 
A5  405  340  97.5  125  35.40 
A6  290  340  40  125  20.28 
B3  730  340  193.3  125  58.42 
C3  730  340  193.3  83  58.19 
Dimensions of a GFRP plate and its openings.
In specimens A5 and A6, which did not meet those conditions, the concrete exhibited brittle failure before the plate reached the limit of its maximum strength. Specimen C3, which met the ratio condition but not the size condition, showed lower maximum shear strength than Specimen B3 did, which met both conditions. Therefore, if the opening size is larger than 100
Figure
Loaddeflection curves for three different arrays of openings in GFRP shear reinforcement.
To examine the influence of the amount of shear reinforcement on shear strength, we designed each specimen with different amounts of reinforcement. The amount of shear reinforcement was the product of the number of vertical components in the critical shear span (
Loaddeflection curves for amount of shear reinforcement.
Ratio of test results to theoretical predictions of shear strength (
All of the specimens, except A5 and A6, showed similar ratios of shear strength. In contrast, specimens A5 and A6 showed only 80–90% of the calculated value. Because the plate had insufficient opening size and ratio of the area of openings, brittle failure occurred in specimens A5 and A6 before the shear reinforcement reached the limit of its maximum strength.
Figure
Effect of the GFRP stripwidthtospacing ratio on shear strength.
Table
Experimental results and ratio of shear strength.
Specimen 







(kN)  (kN)  (kN)  (kN)  
A1  164.55  38.68  16.12  288.60  1.41  1.60 
A2  164.55  58.02  24.18  295.87  1.33  1.57 
A3  164.55  96.71  40.29  388.42  1.49  1.90 
A4  164.55  135.39  56.41  449.88  1.50  2.04 
A5  164.55  251.44  104.76  374.37  0.90  1.39 
A6  164.55  418.47  174.36  475.14  0.81  1.40 
B3  164.55  107.22  44.67  436.32  1.61  2.09 
C3  164.55  107.22  44.67  378.97  1.39  1.81 
In this study, to analyze the shear performance of concrete beams with embedded GFRP plates with openings, we selected the array of openings, ratio of the area of openings, amounts of shear reinforcement, and GFRP stripwidthtostripspacing ratio as variables. We used the shear strength equations in ACI 31814 and ACI 440.1R to compare the experimental and theoretical shear strengths. We draw the following conclusions:
The width and height of the opening should be larger than 100
Three different results from three different shapes of reinforcing plates show that increasing the bonded area between the GFRP plate and the concrete increases the performance of the shear reinforcement, provided the basic conditions are met.
Analysis of the GFRP stripwidthtospacing ratio showed that as the ratio increased, the bonded area increased, which improved resistance to shear cracks.
The equations in ACI 318 and ACI 440.1R yielded generally conservative shear strength results. The ACI 318 code gives a mean value of 1.46 with a standard deviation of 0.1. The ACI 440.1R code gives a mean value of 1.83 with a standard deviation of 0.2. Therefore, the shear strength equation in ACI 318 was more applicable than that in ACI 440.1R to the GFRP platereinforced concrete beams.
Shear spantodepth ratios
Sectional area of a vertical strip of FRP plate (mm^{2})
Web width (mm)
Distance from extreme compression fiber to centroid of longitudinal tension reinforcement (mm)
Specified compressive strength of concrete (MPa)
Specified tensile strength of FRP plate (MPa)
Number of vertical components of the FRP plate within the critical shear span
Centertocenter spacing of longitudinal shear reinforcement (mm)
Thickness of FRP plate (mm)
Nominal shear strength provided by concrete (kN)
Shear strength provided by experiment (kN)
Nominal shear strength provided by FRP plate (kN)
Nominal shear strength (kN)
Width of FRP plate (mm)
Angle between shear reinforcement and longitudinal axis of the member (°)
Ratio of
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (NRF20110016332).