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Strengthening of slab-column connections against punching shear using FRP materials: state-of-the-art review.

1. Introduction

Reinforced concrete (RC) flat slab systems are widely used in commercial and residential construction. The main motivations for the use of this type of slabs are shorter construction times, more economical formwork, minimum structural depth and architectural convenience. The main disadvantage, however, is their weak resistance against punching shear in the area of column connections. This abrupt failure reduces the load-bearing capacity of the slab and can potentially result in the progressive collapse of the entire structure. Further, during its life, an RC slab can deteriorate due to environmental effects such as: fire damage, freezing and thawing and corrosion of embedded reinforcement. Furthermore, a large number of existing concrete structures have been designed using older design codes which do not satisfy current seismic design specifications, particularly in relation to shear strength and ductility (Adhikary and Mutsuyoshi 2006). Many investigations have confirmed that many earthquakes and fire-damaged structures do not have shear reinforcement because of either design errors or poor detailing (Bencardino, Spadea, and Swamy 2007). Existing structures can be replaced with new ones; however, replacing deteriorated and inadequate structures is often not a feasible solution because it involves huge expense. Therefore, the strengthening and/or repair of deficient structures represent an acceptable solution, saving construction time and money. The strengthening technique usually requires increasing the flexural and shear capacity of the existing structure or controlling cracking and deflections. However, the performance of the selected technique is dependent on many factors, including the time to complete the strengthening process, the cost of the applied material and the human resources mobilised (Thanoon et al. 2005).

Traditional strengthening methods such as attaching a steel plate to the tensile face of the structure using adhesive material or steel bolts have been used (Barnes et al. 2001; Sharif et al. 1994); however, steel plates may corrode and need protection themselves.

Recently, fibre-reinforced polymers (FRP) have become a viable solution for rehabilitating and strengthening existing structures in preference to traditional strengthening materials such as steel. FRP offers many advantages such as high tensile strength, light weight, durability and ease of installation and is non-corrosive in nature (Khalifa, Belarbi, and Nanni 2000). Many studies have investigated the strengthening of beams and columns with FRP (Rizzo and De Lorenzis 2009; Sundarraja and Rajamohan 2009). These have concluded that FRP is able to significantly improve the shear and flexural capacity of beams and columns. FRP composites were also used successfully to improve the shear capacity of the slab (Harajli, Soudki, and Kudsi 2006; Soudki, El-Sayed, and Vanzwol 2012).

Strengthening of slabs for shear can be divided into two main methods:

(1) indirect shear strengthening (flexural strengthening) by improving flexural strength via applying CFRP sheets/plates on the tension face of the slab (Soudki, El-Sayed, and Vanzwol 2012) and,

(2) direct shear strengthening (punching shear strengthening) by improving shear strength via inserting shear reinforcements through the thickness of the slab (Meisami, Mostofinejad, and Nakamura 2015).

This paper offers a review of representative experimental studies carried out on slab-column connections using FRP composites. In addition, it presents information about how to apply the strengthening material to RC slab with the aid of an appropriate diagram, and description of the behaviour of strengthened slabs is presented. Databases are also assembled based on the available tests results.

2. Indirect shear strengthening method (Flexural strengthening)

2.1. Bonding FRP sheets or laminates to the concrete

Shear strength of slab is provided by four different parameters. These parameters are: aggregate interlock, uncracked concrete above the neutral axis, residual tensile stress across inclined cracks and longitudinal reinforcement dowelling (Soudki, El-Sayed, and Vanzwol 2012). The shear strength of slabs increases with increase in flexural reinforcement ratio (Alam, Amanat, and Seraj 2009; Ebead and Marzouk 2004; Gardner 2005; Marzouk and Hussein 1991; Ozden, Ersoy, and Ozturan 2006). Increasing the amount of flexural reinforcement reduces the depth and width of the cracks, resulting in an increased contribution of the aggregate interlock as well as the contribution of uncracked concrete to the punching capacity. Ebead and Marzouk (2004) confirmed that the capacity of an RC slab with a reinforcement ratio 0.5% was 1.32 times that of a slab with a reinforcement ratio of 0.35%. However, it is important to point out that higher reinforcement ratios reduce the ductility of the structure (Koppitz, Kenel, and Keller 2013) and the slabs are likely to fail in punching shear mode (Ebead and Marzouk 2004; Marzouk and Hussein 1991).

Furthermore, a concentration of the flexural reinforcement in the column zone contributes to an improvement of the punching shear resistance, crack width and post-cracking stiffness (Lee et al. 2009; McHarg et al. 2000). Therefore, it is expected that applying external FRP sheets/strips to the tension face of a slab will improve the shear capacity of the strengthened slab (El-Salakawy, Soudki, and Polak 2004; Farghaly and Ueda 2011; Harajli and Soudki 2003; Polies, Ghrib, and Sennah 2010; Sharaf, Soudki, and Van Dusen 2006; Soudki, El-Sayed, and Vanzwol 2012).

A strengthening technique using flexible CFRP sheets of 0.13-mm thick was investigated by Harajli and Soudki (2003). CFRP sheets were located close to the column face in two perpendicular directions, and extended along the full dimensions of the slab in order to provide a sufficient bond length of the CFRP sheets. The increase in the shear strength capacity of the strengthened specimens with one layer of the CFRP sheet was 45% greater than that of the control. This improvement in shear capacity is mainly attributed to the role of the CFRP in restricting the growth of the shear and flexural cracks.

Multiple layers of CFRP sheets have also been investigated (Harajli and Soudki 2003). However, the results indicated that no improvement was observed in the shear capacity with respect to one layer of CFRP material. This is because the increase in CFRP reinforcement leads to an increase in the horizontal shear force between the concrete and the strengthening material, resulting in premature bond failure which leads to lower flexural and shear capacity.

Research by Sharaf, Soudki, and Van Dusen (2006) showed that a slab reinforced with a large number of FRP sheets demonstrated a slightly increased load capacity. Also, it is hard to measure the punching shear failure plane when using a large amount of FRP sheet because the shear cracks may be concealed under the CFRP sheets (Soudki, El-Sayed, and Vanzwol 2012).

Other researchers have attempted to apply CFRP sheet on the tension and compression sides of the slab; however, the performance of the strengthened slab did not improve over that of the slab with CFRP on the tension surface only (Robertson and Johnson 2004).

Further research conducted by Soudki, El-Sayed, and Vanzwol (2012) investigated the effect of the locations and inclination of CFRP laminates in relation to the column face or column corner on improving the shear capacity of the slab-column connection. They used six square slabs with dimensions of 1220 mm x 1220 mm x 100 mm reinforced with the same amount of tension reinforcement. All specimens were simply supported along their edges. The testing load was monotonic loading applied through the column stub. As shown in Figure 1, orthogonal and skewed arrangements of the CFRP strips were bonded to the column face or at 1.15 d (d = effective depth of the slab) away from the column corner. The numbers that are shown in Figure 1 refer to the locations of the strain gauges. The experimental results demonstrated that the skewed strips arrangement was the most effective configurations. For orthogonal strengthening, the increase in punching capacity was 12.9% compared to the control specimen, while for skewed strengthening it was 29.1%.

The skewed orientation of the CFRP strips restricted the growth of the radial tension cracks that resulted due to punching shear failure. The failure mode of all the tested slabs was punching shear, resulting in debonding of the strips from the concrete surface, as can be seen in Figure 2.

The advantages of bonding FRP reinforcement on the tension face of existing slabs have been demonstrated by Shahawy et al. (1996) and Teng et al. (2000). However, many existing challenges have contributed to the reduction of the growth of this technique (Grelle and Sneed 2013). Debonding failure is one of the inherent shortcomings of the external FRP application, which happens when FRP sheets/laminates detach from the RC surface due to the low tensile strength of the concrete (Ceroni et al. 2008).

The anchorage of FRP composites provides a good solution to these problems (Ceroni et al. 2008; Smith et al. 2011; Zhang and Smith 2012). However, the effectiveness of the anchorage system is strongly influenced by the detailing and application procedure of the system.

Several FRP anchorage systems applied in external shear strengthening of RC elements were compiled and catalogued by Kalfat, Al-Mahaidi, and Smith (2013); they also quantified the efficiency factor for each anchorage concept. In the case of slabs, some investigators have studied the possibility of increasing the end anchorage of the FRP sheet with concrete, by adding transverse layers of FRP strips at the end of the strengthening material. The anchorage using FRP strips is typically applied in the plane of the FRP sheet and installed perpendicularly to the direction of force in the FRP sheet. A review by Grelle and Sneed (2013) described the limitations and advantages of this anchorage type.

Ebead and Marzouk (2004) added transverse layers of CFRP strips (100 mm wide and 500 mm long) at the end of the CFRP sheets (300 mm width) which were applied to the tension face of concrete. The anchorage system contributed to the prevention of premature bond failure at the end of the FRP reinforcement. The average gain in the load capacity of the strengthened specimen was approximately 40% higher than that of the unstrengthened specimen.

To further understand the effect of end anchorage, the application of CFRP strips at the ends of the strengthening material was also investigated by Sharaf, Soudki, and Van Dusen (2006). A total of six slab-column connections with a column extending from the top and bottom slab surfaces were tested. The CFRP laminates were bonded to the tension face of the concrete in two different patterns: orthogonal and skewed. The findings of this study indicated that the slabs with the orthogonal and the skewed configurations had almost the same increase in ultimate load capacity of 6 and 7% over the control, respectively. However, specimens with FRP laminates had less deflection at ultimate load than the unstrengthened specimen due to the stiff behaviour of the CFRP-strengthened specimen. With regard to the crack patterns, all strengthened specimens failed in punching shear mode after a series of diagonal shear cracks formed around the column. As can be seen in Figure 3, the CFRP laminates did not display bond failure at their anchored ends.

Wrapping flexible FRP sheet around RC beams has been proved as an efficient way to increase their strength and ductility (Ceroni et al. 2008). This idea has been tested on a slab-column edge connection by El-Salakawy, Soudki, and Polak (2004). Both carbon and glass FRP sheets were used with different widths and displacements as shown in Figure 4(a). In addition to the FRP sheets that were bonded to the tension face of the slab, one layer of an L-shaped FRP sheet was wrapped around the thickness of the slab. An example of wrapping sheets is shown in Figure 4(a, b). According to the results, there was no significant improvement in the ultimate load capacity and ductility of the strengthened slab. The failure occurred after the bonding between the FRP and the concrete in the area adjacent to the column had happened. In practice, flat slabs are usually subjected to eccentric loading, due to unequal spacing of columns, unequal load distributions on each side of the column and lateral loading problems. Therefore, some research has focused on strengthening and repairing such slabs using externally bonded FRP (Polies, Ghrib, and Sennah 2010; Robertson and Johnson 2004). For example, after testing to 5% lateral drift, Robertson and Johnson (2004) repaired RC slab-column connections using epoxy and CFRP sheets. The experimental work consisted of testing three large-scale RC slab-column connections with dimensions 3000 x 2750 x 115 mm. The specimens were repaired after testing to 5% lateral drift. Low viscosity epoxy was used to fill the cracks which occurred during the testing. Four The CFRP sheets were then applied on either side of the column the tension face of the cracked slabs. The results confirmed that the technique is effective in restoring both the initial stiffness and ultimate strength of the original specimen.

2.2. Prestressed FRP sheets or plates

Prestressed FRP sheets or plates can also be used as an external strengthening material. By prestressing the sheets, the load-bearing capacity is improved under service and ultimate conditions. It also contributes to reducing the deflections, increasing the cracking loads and closing the existing cracks (Wight, Green, and Erki 2001). Despite these advantages, only limited research has been undertaken to date, primarily because of the additional labour required and anchors issues. Applying prestress force to FRP requires an adequate anchorage system to preventing peeling-off failure that may occurred at the ends of the sheet (El-Hacha, Wight, and Green 2001; Kim et al. 2008).

Kim et al. (2008) found that 15% of the sheet strength was a desirable stressing level to avoid the debonding failure of the sheet. Several existing prestressing methods have been reported by El-Hacha, Wight, and Green (2001).

Kim et al. (2010) attempted to investigate the punching behaviour of RC slab strengthened with prestressed CFRP sheets. They induced 60 MPa prestress into 0.165 mm thick CFRP sheets by tensioning them using an integrated anchor system which consists of a jacking anchor and a fixed anchor. Details of the anchorage system are shown in Figure 5. The experimental programme consisted of four slabs with dimensions of 2360 mm x 2360 mm x 150 mm that were tested under concentric load. One specimen served as a control (B3-SL1), one specimen was strengthened with non-prestressed CFRP sheet (B3-SL2) and the others were strengthened with prestressed sheets (B3-SL3 & B3-SL4). All CFRP sheets (non-prestressed and prestressed) were applied at a distance of 1.5 times the effective depth of the slab in order to effectively intercept the inclined shear cracks.

The prestressed sheet was able to increase the ultimate load and the cracking load up to 20 and 25%, respectively, compared to the control slab. All tested slabs failed in punching shear mode. For the non-prestressed slab, the initial cracks formed at the edge of the sheets due to a high stress concentration between the strengthening material and the concrete. At a high level of the load, delamination of the CFRP sheet was observed spreading in all directions. In the slab strengthened with a prestressed sheet, the cracks also appeared at the edge of the sheets, but they were much thinner than those in the non-prestressed system. A partial delamination of the CFRP sheets was observed, after the finer cracks connected together. Figure 6 shows the failure mode for the four tested specimens. Recently, punching shear behaviour of slab strengthened with prestressed FRP plates has been studied by (Abdullah, Bailey, and Wu 2013). The study concentrated on a slab without shear reinforcement and reinforced with a low flexural reinforcement ratio. The experimental results showed that the strengthening method increase the load capacity by 43% over the reference slab (without strengthening).

3. Direct shear strengthening method (Punching shear strengthening)

One of the most effective ways to improve the strength and deformation capacity of a flat slab is to provide shear reinforcement in the vicinity of the columns (Fernandez, Muttoni, and Jakob 2010; Heinzmann et al. 2012; Polak 2005; Worle 2014). Investigations carried out on slab-column connections indicated that the shear strength and ductility of the slab are considerably increased by additional shear reinforcement (Dilger 2000) as shown in Figure 7. It is also interesting that the rotation of the slab also increased (Fernandez, Muttoni, and Jakob 2010). The shear failure plane of the slabs strengthened externally with FRP reinforcements was approximately the same as that of the unstrengthened specimen (Harajli and Soudki (2003); El-Salakawy, Soudki, and Polak (2004)). It was expected that using shear bolts would push the shear plane further from the column perimeter due to the large shear capacity provided by the shear reinforcement. Therefore, external strengthening with FRP reinforcement was combined with additional vertical shear reinforcement to increase the shear and deformation capacities to reasonable values.

However, the slab with shear reinforcement failed in other failure modes, as shown in Figure 8. The failure modes include (1) crushing of compression strut; (2) failure inside the shear reinforced region; (3) failure outside the shear reinforced region (Fernandez and Muttoni 2009).

The providing of shear reinforcement in existing slabs was studied by El-Salakawy, Soudki, and Polak (2004). In their study, the slab-column edge connections were bonded with FRP laminates and reinforced with steel bolts installed through small holes located around the column zone. The shear bolts consisted of 12.7 mm bars with two anchored ends, as can be seen in Figure 9. It was concluded that the presence of shear bolts increased the flexural stiffness of the slab and delayed the opening of flexural cracks, resulting in increased shear strength of the strengthened connections, and it also changed brittle failure to ductile failure. The results demonstrated an increase in shear resistance of 23% when CFRP sheets were used alone. However, when the shear bolts were used with FRP sheets, an increase of up to 30% was achieved.

Harajli, Soudki, and Kudsi (2006) used a strengthening technique that was an extension of the method originally proposed by El-Salakawy, Soudki, and Polak (2004). However, they used steel bolts with bearing plates as shown in Figure 10. Hence, the functions of the shear steel bolts were to add confinement pressure on concrete and to transfer the horizontal forces induced between the steel plates and the concrete.

El-Salakawy, Soudki, and Polak (2004) used similar specimens to those used earlier by Harajli and Soudki (2003) to compare the indirect and the direct shear strengthening methods. Single flexible CFRP sheets with widths of 100 mm or 150 mm and an elastic modulus of 230GPa were applied along the full length of the specimen in two perpendicular directions. Steel bolts were arranged in two different configurations. In the first configuration, two rows with four bolts were used, one at each column corners (the inner bolts) and the others in the middle of each column side (the outer bolts). In the second configuration, all eight bolts were arranged in one row at 20 mm from the column sides. Figure 11 shows the two strengthening configurations.

Although all strengthened specimens exhibited greater shear capacity, it was found that the use of a combination of CFRP sheets and shear bolts provided the most noticeable improvement, with increases in shear capacity of 77%. This technique enabled the CFRP sheet to reach an ultimate strain of 9000 [mu][epsilon] (65% of rupture). It is worth mentioning that the two different configurations did not have a significant effect on the load-deflection response of the connection. The previous studies on strengthening of flat slab against punching shear using indirect and direct strengthening methods are summarised in Tables 1 and 2, respectively.

4. Direct strengthening method using FRP reinforcements

This system involves the insertion of FRP reinforcement into holes through the cross section of the element. The holes can be created prior to concrete casting using PVC pipes (Binici and Bayrak 2003) or they are drilled through the slab thickness to simulate an actual flat slab. Creating the holes prior to concrete casting is an acceptable method for testing purposes to avoid any damage in flexural reinforcement during the drilling operation (Erdogan, Binici, and Ozcebe 2010). An additional study confirmed that the use of PVC pipes to simulate drilling of the holes had no influence on the behaviour of the specimens (Binici and Bayrak 2003, 2005b; Sissakis and Sheikh 2007).

The previous experimental investigations have shown that various parameters have an impact on the bond performance of FRP in concrete, including the type of bonding adhesive (Hashemi and Al-Mahaidi 2010; Michael et al. 2008), the concrete strength (Godat et al. 2012) and FRP stiffness (Nakaba et al. 2001). Pullout test has been used to understand and predict the bond-slip behaviour of FRP in concrete and to capture the main features of the FRP contribution to concrete shear strength (Bilotta et al. 2011; De Lorenzis, Rizzo, and La Tegola 2002; Galati and De Lorenzis 2009). In this method, FRP bars, External CFRP stirrups and FRP fans have been used for the strengthening. These methods can be described as follows:

4.1. FRP bars

In practice, the use of FRP rods with epoxy resin in drilled holes has been found to be an easy and suitable procedure for strengthening RC slabs against punching shear failure. The effect of FRP rods bonded with an epoxy adhesive on the shear strength of the slab was investigated by Meisami, Mostofinejad, and Nakamura (2013). The results indicated that the slab strengthened with 24 CFRP bar increased the ultimate load by 67.2% compared to the corresponding control specimen. Increasing the number of CFRP bars from 8 to 24 resulted in changing the failure mode from shear to flexural failure. Furthermore, Meisami, Mostofinejad, and Nakamura (2014) studied the use of CFRP grids fixed in holes drilled with different arrangements around columns of flat slabs for concentric loading. The strengthening method was applied to four specimens and one specimen served as a control without strengthening. The CFRP grids had two side wings which acted as a lateral anchorage around the FRP grid core, as shown in Figure 12. The results showed that the shear capacity of the slab strengthened with 24 of CFRP grids increased to 56.4% compared to that of the control slab. In addition, the failure mode shifted from shear to flexural failure.

Lawler and Polak (2011) used glass fibre-reinforced polymer (GFRP) bolts which were inserted into small holes around the column-slab connection. The rod ends were crimped with aluminium fittings to create a mechanical anchorage for the FRP rod. The details of the proposed shear bolts are shown in Figure 13. Two configurations were applied using this application: an orthogonal and a radial pattern. The results indicated that the presence of the GFRP shear bolts in a radial and an orthogonal arrangement increased the strength of the slab with bolts by up to 22 and 9.88% more than the slab without bolts, respectively. However, the most critical point of this type of application is the anchorage and tightening of the shear bolts assembly to the slab face. It is recommended there is no (or little) movement between the slab face and the end fitting of the shear bolts in order to prevent the development of any axial forces between the FRP anchorage and the concrete surface. In other words, the slab's behaviour was affected by the tightness of the bolts against the slab faces. This explains why the slabs with the orthogonal pattern (where a few of the bolts were not very tightly installed) demonstrated a lower strength than those with the radial pattern (where the bolts were properly installed).

4.2. External CFRP stirrups

Recently, some researchers have investigated the ability of FRP fabrics to enhance shear strength when they are threaded (stitched) through the thickness of the slab creating external stirrups (Binici and Bayrak 2003; Sissakis and Sheikh 2007).The stitching procedures mentioned in Binici and Bayrak (2005a) are as follows. First, the CFRP strips are impregnated with epoxy before inserting them into pre-opened holes around the column-slab connection, and the CFRP strips are then looped between pairs of holes continuously to form closed stirrups. After the completion of the stitching (wrapping) process, additional CFRP sheets are bonded to the tensioned side to close the holes prior to filling them with a bonding material. Binici and Bayrak (2003) showed that the use of diagonal CFRP strips eliminated the possibility of punching failure inside the shear reinforced zone, as shown in Figure 14. Using a sufficient number of CFRP stirrups increased the punching shear strengths of the test specimens by up to 51% relative to the control specimens. The post-punching behaviour of the FRP slab was also significantly better than that of the unstrengthened slab.

Further research conducted by Sissakis and Sheikh (2007) involved the testing of 28 square slabs of 1500-mm side length with 150-mm thickness. They used CFRP sheet that was cut from strands. A typical strengthened slab is shown in Figure 15. The results showed that the proposed method had a significant effect in increasing the shear strength, energy dissipation and ductility of the strengthened slabs. The shear strength and ductility of the strengthened slab increased by up to 80 and 700%, respectively, relative to the control slab. The concept of stitching CFRP through the thickness of RC slabs has also been extended to cases of flat slabs with combined gravity shear and unbalanced moment. For example, Binici and Bayrak (2005a) showed that the proposed method can improved the shear capacity of a slab-column connection subjected to shear forces and unbalanced moments by 60%.

4.3. FRP fans

Recently, FRP fabrics have been used as shear reinforcement to carry the diagonal tension forces when they are threaded through the thickness of the slab. The fibre ends are splayed out on the concrete surface in a fan shape and bonded with epoxy in order to avoid local stress concentrations and to provide good anchorage; here this is referred to as the FRP fan. Because the anchor is manufactured by hand, variations between individual anchors occur. However, Zhang, Smith, and Kim (2012) found that the performance of the anchorage system was not significantly affected by these variations. Smith et al. (2011) discussed the effectiveness of the type and position of the FRP anchor fan in enhancing the strength and deflection of FRP-strengthened RC slabs. Erdogan, Binici, and Ozcebe (2010) used this method to increase the shear resistance of the existing slab. The strengthening method consisted of cutting unidirectional CFRP sheets into rectangular pieces with dimensions of 250 x 120 mm and then impregnating them with two component structural epoxy resin (parts A and B). After the impregnation process, the CFRP sheets were rolled around a steel bar with a diameter of 6 mm to create CFRP dowels with dimensions of 25 x 250 x 0.165 mm. This steel bar was used to provide a cost-effective stiff material and it was removed after installing CFRP strips through the holes. The free ends of the CFRP dowels passed through additional CFRP patches which were bonded to the concrete faces. Finally, the free ends of the CFRP dowels were fanned out to create the FRP anchor fan. Figure 16 shows the steps of the strengthening method. The strengthened specimen with the highest number of CFRP fans showed the highest strength enhancement (33.4%), post-punching improvement (135.5%) and the displacement value increased (180.6) compared to the unstrengthened specimen. It can be claimed that the fixed-end conditions of the FRP fan have a significant effect on increasing the efficiency of this method.

Meisami, Mostofinejad, and Nakamura (2015) showed that, for the same slab, strengthening with FRP fans resulted in a higher shear capacity than other strengthening methods using FRP rod or screws and nuts, which had been previously investigated (Meisami, Mostofinejad, and Nakamura 2013, 2014). Using approximately eight 12.6 [mm.sup.2] FRP fans (which corresponds to the area of a circular section with a 4-mm diameter), punching capacity increased by 33.3%, compared to that obtained for the control (Meisami, Mostofinejad, and Nakamura 2015). However, strengthening of the same RC slab with eight 8-mm screws and nuts or with eight 12-mm FRP rods showed an increase in shear capacity equal to 17 and 11% over the unstrengthened slab, respectively (Meisami, Mostofinejad, and Nakamura 2013).

5. Advantages and disadvantages of indirect and direct shear strengthening methods

In Table 3, a further discussion of advantages and disadvantages of the flexural and the shear strengthening methods is highlighted.

6. Conclusions

Based on the previous studies, the following conclusions can be drawn:

(1) Strengthening of flat slab against punching shear failure using FRP composites is one method by which the shear capacity of deficient slabs may be improved.

(2) Bonding FRP reinforcement to the tension face of RC slabs increases their shear strength to a certain level. After that level, any increase in the amount of FRP reinforcement does not have a significant effect on the shear capacity or the stiffness of the strengthened slab.

(3) Slabs with only FRP flexural reinforcement without shear reinforcement have a flexural failure mode with little ductility.

(4) Strengthening slabs using FRP sheet/strips without shear bolts has no effect on the position of the shear failure plane. However, using a combination of FRP and shear bolts or only shear bolts pushes the shear failure further outward compared with the control specimen.

(5) Increasing the area of FRP reinforcement in the flexural strengthening method reduces the ductility of the slab and the strengthened slab fails in punching shear mode. However, in the case of the punching strengthening method, the shear capacity increases and the strengthened slab fails in flexural mode with higher deformation.

(6) Punching shear strengthening method is more effective than the flexural method in terms of increasing the load and deformation capacities. However, the reinforcement details of the existing slab should be known to avoid their damage during the drilling process.

(7) Although the benefits of using FRP as vertical shear reinforcements have been widely acknowledged by researchers, more studies are required to measure the effect of the number, dimensions and spacing between the holes on the behaviour of the FRP strengthened slab.

ARTICLE HISTORY

Received 31 May 2016

Accepted 6 April 2018

https://doi.org/10.1080/13287982.2018.1462901

Acknowledgements

The scholarship support provided to the first author by Ministry of Higher Education and Scientific Research in Iraq (MoHESR) is gratefully acknowledged. The technical support provided by staff of the Smart Structures Laboratory of Swinburne University of Technology is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Haifa Saleh is a PhD student in Swinburne University of Technology. Prior to joining to Swinburne University of Technology, she worked as an engineer in Department of Engineering Affairs in Iraq and lecture for undergraduate students in Tikrit University/Iraq. She received her BSc in Civil Engineering in 2001 and MSc in Structural Engineering from Tikrit University-Iraq in 2007.

Kamiran Abdouka is a part-time senior lecturer in Structural Engineering at the Faculty of Engineering and Industrial Sciences--Swinburne University of Technology in Melbourne. He received his BSc in Civil Engineering in 1984 and MSc in Structural Engineering from the University Baghdad-Iraq in 1989 and PhD in Civil Engineering in 2003 from the University of Melbourne. He is a member of Engineers Australia and a registered building practitioner in Victoria as a civil engineer. His areas of expertise are Reinforced and Prestressed Concrete Design, Assessment of deterioration in buildings, strengthening of Swinburne University of Technology concrete structures and Seismic design of structures.

Riadh Al-Mahaidi is a professor of Structural Engineering and director of the Smart Structures Laboratory at Swinburne University of Technology in Melbourne. He also holds the position of vice president (International Engagement) at Swinburne. Over the past 15 years, Al-Mahaidi focused his research and practice on lifetime integrity of bridges, particularly in the area of structural strength assessment and retrofitting using advanced composite materials. He is currently leading a number of research projects on strengthening and durability of concrete bridges using fibre-reinforced polymers combined with cement-based bonding agents and fatigue life improvement of metallic bridges using advanced composite systems. He has recently been engaged with the field of hybrid testing combined with multi-axis sub-structuring systems applied to bridges and buildings using the new MAST-Hybrid testing facility at Swinburne. Al-Mahaidi published more than 400 technical papers in international journals and conferences and more than 50 technical reports relating to structural assessment and strengthening.

Robin Kalfat is an internationally recognised expert in the field of fibre-reinforced polymers (FRPs) used to strengthening RC structures. He was awarded a PhD from Swinburne University of Technology after completing a research project focusing on anchorage systems in concrete structures strengthened with FRP and later joined Swinburne in November 2013 as a postdoctoral research fellow. During his research career, he has contributed by publishing 16 peer-reviewed papers in high-quality journals and has actively sought collaboration through involvement with national and international standards committees, supervision of PhD students and teaching of undergraduate students. Prior to joining Swinburne, he has gained over 10 years of design experience in Australia as well as internationally (UK and Dubai) in the area of strengthening of existing structures using FRP for SRG Limited.

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Harajli, M. H., K. A. Soudki, and T. Kudsi. 2006. "Strengthening of Interior Slab-column Connections Using a Combination of FRP Sheets and Steel Bolts." Journal of Composites for Construction 10 (5): 399-409. doi:10.1061/(ASCE)1090-0268(2006)10:5(399).

Hashemi, Slavash, and Riadh Al-Mahaidi. 2010. "Investigation of Bond Strength and Flexural Behaviour of FRP-strengthened Reinforced Concrete Beams Using Cement-Based Adhesive." Australian Journal of Structural Engineering 11: 129-139.

Heinzmann, D., S. Etter, S. Villiger, and T. Jaeger. 2012. "Punching Tests on Reinforced Concrete Slabs with and without Shear Reinforcement." ACI Structural Journal 109 (6): 787-794.

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Khalifa, Ahmed, Abdeldjelil Belarbi, and Antonio Nanni. 2000. "Shear Performance of RC Members Strengthened with Externally Bonded FRP Wraps." In Proceedings of the 12th World Conference on Earthquake Engineering, Auckland, New Zealand.

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Kim, Y. J., J. M. Longworth, R. G. Wight, and M. F. Green. 2010. "Punching Shear of Two-way Slabs Retrofitted with Prestressed or Non-Prestressed CFRP Sheets." Journal of Reinforced Plastics and Composites 29 (8): 1206-1223. doi:10.1177/0731684409103143.

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Lawler, Nicholas, and Maria Anna Polak. 2011. "Development of FRP Shear Bolts for Punching Shear Retrofit of Reinforced Concrete Slabs." Journal of Compisites for Construction 15 (4): 591-601. doi:10.1061/(ASCE) CC.1943-5614.0000188.

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McHarg, Peter J., William D. Cook, Denis Mitchell, and S. Yoon. 2000. "Benefits of Concentrated Slab Reinforcement and Steel Fibers on Performance of Slab-column Connections." Aci Structural Journal 97 (2): 225-234. doi:10.14359/851.

Meisami, M. Hasan, Davood Mostofinejad, and Hikaru Nakamura. 2013. "Punching Shear Strengthening of Two-way Flat Slabs Using CFRP Rods." Composite Structures 99: 112-122. doi:10.1016/j.compstruct.2012.11.028.

Meisami, M. Hasan, Davood Mostofinejad, and Hikaru Nakamura. 2014. "Punching Shear Strengthening of Two-way Flat Slabs with CFRP Grids." Journal of Composite for Construction 18: 1-10. doi:10.1061/(ASCE)CC.1943-5614.0000443.

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Haifa Saleh ([double dagger]), Kamiran Abdouka, Riadh Al-Mahaidi and Robin

Kalfat

Faculty of science, Engineering and Technology, swinburne university of

Technology, Melbourne, Australia

CONTACT Haifa saleh ([mail]) hsaleh@swin.edu.au

([double dagger]) Civil Engineering Department, University of Tikrit, Iraq

Caption: Figure 1. CFRP strengthening schemes (Soudki, El-Sayed, and Vanzwol 2012).

Caption: Figure 2. Debonding failure (Soudki, El-Sayed, and Vanzwol 2012).

Caption: Figure 3. Punching shear failure cracks (Sharaf, Soudki, and Van Dusen 2006).

Caption: Figure 4. (a) Plan view (b) side view of L-shaped of FRP sheet (El- Salakawy, Soudki, and Polak 2004).

Caption: Figure 5. Typical experimental test (a) CFRP strengthening scheme; (b) jacking anchor; (c) fixed anchor (Kim et al. 2010).

Caption: Figure 6. Typical failure mode of tested slabs: (a) control (B3-SL1); (b) nonprestressed CFRPs (B3-SL2); (c) prestressed CFRPs (B3-SL3); (d) CFRP sheets removed after test (B3-SL4) Kim et al. (2010).

Caption: Figure 7. Influence of shear reinforcement on strength and ductility of slab (Dilger 2000).

Caption: Figure 8. Possible failure modes of flat slabs with punching shear reinforcement: (a) Crushing of compression strut; (b) failure within the region of the shear reinforcement and (c) failure outside the shear reinforced zone (Fernandez and Muttoni 2009).

Caption: Figure 9. Shear reinforcement (steel bolt).

Caption: Figure 10. Steel bolts with bearing plates and strain gauge (Harajli, Soudki, and Kudsi 2006).

Caption: Figure 11. Specimens dimension and strengthening details (Harajli, Soudki, and Kudsi 2006).

Caption: Figure 12. Arrangements of FRP grid around the column (Meisami, Mostofinejad, and Nakamura 2014).

Caption: Figure 13. GFRP shear bolts (Lawler and Polak 2011).

Caption: Figure 14. Failure surfaces and cross sections of the slab (Binici and Bayrak 2003).

Caption: Figure 15. Slab after strengthening with CFRP laminate (Sissakis and Sheikh 2007).

Caption: Figure 16. Strengthening steps: (a) manufacturing the dowels; (b) installation of dowels through the thickness; (c) Installation of CFRP patches at the ends; (d) fanning out (anchoring) the dowel ends (Erdogan, Binici, and Ozcebe 2010).
Table 1. Indirect shear strengthening method.

                                                                  B

Author                     Specimen            Comments           mm

Bonding CFRP sheets

Harajli and Soudki           SA1               Contrail          670
(2003)

Harajli and Soudki          SA1F5             One layer          670
(2003)

Harajli and Soudki          SA1F10            One layer          670
(2003)

Harajli and Soudki          SA1F15            One layer          670
(2003)

Harajli and Soudki           SA2              Control 2          670
(2003)

Harajli and Soudki          SA2F10            One layer          670
(2003)

Harajli and Soudki          SA2F15            One layer          670
(2003)

Harajli and Soudki          SA2F20            One layer          670
(2003)

Harajli and Soudki           SB1              Control 3          670
(2003)

Harajli and Soudki          SB1F10            One layer          670
(2003)

Harajli and Soudki          SB1F15            One layer          670
(2003)

Harajli and Soudki        SB1F10(2L)          Two layers         670
(2003)

Harajli and Soudki           SB2               Control4          670
(2003)

Harajli and Soudki          SB2F15            One layer          670
(2003)

Harajli and Soudki          SB2F20            One layer          670
(2003)

Harajli and Soudki        SB2F15(2L)          Two layers         670
(2003)

El-Salakawy, Soudki,         XXX         Control slab without    1540
and Polak (2004)                               opening

Bonding CFRP sheets

El-Salakawy, Soudki,        SX-CF          One layer CFRP L      1540
and Polak (2004)                                shaped

Bonding GFRP sheets

El-Salakawy, Soudki,        SX-GF          One layer GFRP L      1540
and Polak (2004)                                shaped

El-Salakawy, Soudki,         SFO          Control slab with      1540
and Polak (2004)                               opening

El-Salakawy, Soudki,        SH-GF        Two layers U shaped     1540
and Polak (2004)                                 GFRP

Bonding CFRP
laminates

Soudki, El-Sayed,          Control             Control           1220
and Vanzwol (2012)

Soudki, El-Sayed,          S-4-0-0           4 laminate;         1220
and Vanzwol (2012)                          orthogonal and
                                          offset column face

Soudki, El-Sayed,          S-4-0-A           4 laminate;         1220
and Vanzwol (2012)                          Orthogonal and
                                          adjacent to column
                                                 face

Soudki, El-Sayed,          S-4-S-0        4 skewed laminate;     1220
and Vanzwol (2012)                        adjacent to column
                                                 face

Soudki, El-Sayed,          S-4-S-A        4 skewed; laminate     1220
and Vanzwol (2012)                         and adjacent to
                                                column

Soudki, El-Sayed,          S-8-O-AO          8 laminate;         1220
and Vanzwol (2012)                          orthogonal and
                                          adjacent to column

Ebead and Marzouk         Ref-0.35%            Control           1900
(2004)

Ebead and Marzouk        CFRP-F0.35%       Two layers CFRP       1900
(2004)                                          125kN

Ebead and Marzouk         Ref- 0.5%            Control           1900
(2004)

Ebead and Marzouk         CFRP-FO.5%        CFRP laminate,       1900
(2004)                                     preloaded 165kN

Sharaf, Soudki, and        Control             Control           2000
Van Dusen (2006)

Sharaf, Soudki, and        4-0-CFRP          4 laminate;         2000
Van Dusen (2006)                              orthogonal

Sharaf, Soudki, and        4-S-CFRP          4 laminate;         2000
Van Dusen (2006)                          orthogonal Skewed

Sharaf, Soudki, and        8-0-CFRP          8 laminate;         2000
Van Dusen (2006)                              orthogonal

Sharaf, Soudki, and        8-S-CFRP       8 laminate; skewed     2000
Van Dusen (2006)

Sharaf, Soudki, and       8-0&S-CFRP         8 laminate;         2000
Van Dusen (2006)                         orthogonal &8 skewed

Bonding GFRP
laminates

Chen and Li (2005)        SRI-CI-F0            Control           1000

Chen and Li (2005)        SR1-C1-F1         One layer GFRP       1000

Chen and Li (2005)        SR1-C1-F2        Two layers GFRP       1000

Chen and Li (2005)        SR1-C2-F0            Control           1000

Chen and Li (2005)        SR1-C2-F1         One layer GFRP       1000

Chen and Li (2005)        SR1-C2-F2        Two layers GFRP       1000

Chen and Li (2005)        SR2-C1-F0            Control           1000

Chen and Li (2005)        SR2-C1-F1         One layer GFRP       1000

Bonding GFRP
laminates

Chen and Li (2005)        SR2-C2-F2        Two layers GFRP       1000

Chen and Li (2005)        SR2-C1-F2        Two layers GFRP       1000

Chen and Li (2005)        SR2-C2-F0            Control           1000

Chen and Li (2005)        SR2-C2-F1         One layer GFRP       1000

Prestressed sheet

Kim et al. (2010)           B3-SL1             Control           2360

Kim et al. (2010)           B3-SL3        Prestressed sheet      2360

Kim et al. (2010)           B3-SL4        Prestressed sheet      2360

Prestressed plates

Abdullah, Bailey,            RS0               Control           1800
and Wu (2013)

Abdullah, Bailey,           RS-F7        Prestressing ratio =    1800
and Wu (2013)                                    7.5%

Abdullah, Bailey,           RS-F15       Prestressing ratio =    1800
and Wu (2013)                                    15%

Abdullah, Bailey,           RS-F30       Prestressing ratio =    1800
and Wu (2013)                                    30%

                          L      h     b     l    [f'.sub.c]

                                                      N/
Author                    mm    mm    mm    mm        mm

Bonding CFRP sheets

Harajli and Soudki       670    55    100   100      31.9
(2003)

Harajli and Soudki       670    55    100   100      29.1
(2003)

Harajli and Soudki       670    55    100   100      34.3
(2003)

Harajli and Soudki       670    55    100   100      23.5
(2003)

Harajli and Soudki       670    55    100   100      35.5
(2003)

Harajli and Soudki       670    55    100   100      31.9
(2003)

Harajli and Soudki       670    55    100   100      35.5
(2003)

Harajli and Soudki       670    55    100   100      23.5
(2003)

Harajli and Soudki       670    75    100   100      35.5
(2003)

Harajli and Soudki       670    75    100   100      31.9
(2003)

Harajli and Soudki       670    75    100   100       33
(2003)

Harajli and Soudki       670    75    100   100      34.3
(2003)

Harajli and Soudki       670    75    100   100      29.1
(2003)

Harajli and Soudki       670    75    100   100      29.1
(2003)

Harajli and Soudki       670    75    100   100       33
(2003)

Harajli and Soudki       670    75    100   100      34.3
(2003)

El-Salakawy, Soudki,     1020   120   290   270       33
and Polak (2004)

Bonding CFRP sheets

El-Salakawy, Soudki,     1020   120   290   270       32
and Polak (2004)

Bonding GFRP sheets

El-Salakawy, Soudki,     1020   120   290   270       32
and Polak (2004)

El-Salakawy, Soudki,     1020   120   290   270      31.5
and Polak (2004)

El-Salakawy, Soudki,     1020   120   290   270       32
and Polak (2004)

Bonding CFRP
laminates

Soudki, El-Sayed,        1220   100   150   150      25.8
and Vanzwol (2012)

Soudki, El-Sayed,        1220   100   150   150      25.8
and Vanzwol (2012)

Soudki, El-Sayed,        1220   100   150   150      25.8
and Vanzwol (2012)

Soudki, El-Sayed,        1220   100   150   150      25.8
and Vanzwol (2012)

Soudki, El-Sayed,        1220   100   150   150      25.8
and Vanzwol (2012)

Soudki, El-Sayed,        1220   100   150   150      25.8
and Vanzwol (2012)

Ebead and Marzouk        1900   150   250   250       30
(2004)

Ebead and Marzouk        1900   150   250   250       29
(2004)

Ebead and Marzouk        1900   150   250   250       35
(2004)

Ebead and Marzouk        1900   150   250   250       34
(2004)

Sharaf, Soudki, and      2000   150   200   200       28
Van Dusen (2006)

Sharaf, Soudki, and      2000   150   200   200       25
Van Dusen (2006)

Sharaf, Soudki, and      2000   150   200   200       28
Van Dusen (2006)

Sharaf, Soudki, and      2000   150   200   200       25
Van Dusen (2006)

Sharaf, Soudki, and      2000   150   200   200       25
Van Dusen (2006)

Sharaf, Soudki, and      2000   150   200   200       28
Van Dusen (2006)

Bonding GFRP
laminates

Chen and Li (2005)       1000   100   150   150      16.9

Chen and Li (2005)       1000   100   150   150      16.9

Chen and Li (2005)       1000   100   150   150      16.9

Chen and Li (2005)       1000   100   150   150      34.4

Chen and Li (2005)       1000   100   150   150      34.4

Chen and Li (2005)       1000   100   150   150      34.4

Chen and Li (2005)       1000   100   150   150      16.9

Chen and Li (2005)       1000   100   150   150      16.9

Bonding GFRP
laminates

Chen and Li (2005)       1000   100   150   150      34.4

Chen and Li (2005)       1000   100   150   150      16.9

Chen and Li (2005)       1000   100   150   150      34.4

Chen and Li (2005)       1000   100   150   150      34.4

Prestressed sheet

Kim et al. (2010)        2360   150   250   250       33

Kim et al. (2010)        2360   150   250   250       33

Kim et al. (2010)        2360   150   250   250       33

Prestressed plates

Abdullah, Bailey,        1800   150   250   250      35.5
and Wu (2013)

Abdullah, Bailey,        1800   150   250   250      35.5
and Wu (2013)

Abdullah, Bailey,        1800   150   250   250      35.5
and Wu (2013)

Abdullah, Bailey,        1800   150   250   250      35.5
and Wu (2013)

                         [rho]   [b.sub.f]    [t.sub.f]    [P.sub.u]

Author                     %         mm           mm           kN

Bonding CFRP sheets

Harajli and Soudki         1         --           --          49.2
(2003)

Harajli and Soudki         1         50          0.13         47.4
(2003)

Harajli and Soudki         1        100          0.13         65.4
(2003)

Harajli and Soudki         1        150          0.13         64.1
(2003)

Harajli and Soudki        1.5        --           --          60.5
(2003)

Harajli and Soudki        1.5       100          0.13         70.1
(2003)

Harajli and Soudki        1.5       150          0.13         77.7
(2003)

Harajli and Soudki        1.5       500          0.13          80
(2003)

Harajli and Soudki         1         --           --          78.8
(2003)

Harajli and Soudki         1        100          0.13        114.5
(2003)

Harajli and Soudki         1        150          0.13         104
(2003)

Harajli and Soudki         1        100          0.13        107.5
(2003)

Harajli and Soudki        1.5        --          0.13         122
(2003)

Harajli and Soudki        1.5       150          0.13        142.3
(2003)

Harajli and Soudki        1.5       200          0.13        118.6
(2003)

Harajli and Soudki        1.5       150          0.13        123.3
(2003)

El-Salakawy, Soudki,     0.75        --           --          125
and Polak (2004)

Bonding CFRP sheets

El-Salakawy, Soudki,     0.75       100          1.2          126
and Polak (2004)

Bonding GFRP sheets

El-Salakawy, Soudki,     0.75       100          0.36         130
and Polak (2004)

El-Salakawy, Soudki,     0.75        --           --          110
and Polak (2004)

El-Salakawy, Soudki,     0.75                    0.36         135
and Polak (2004)

Bonding CFRP
laminates

Soudki, El-Sayed,         1.0       100          1.2         160.3
and Vanzwol (2012)

Soudki, El-Sayed,         1.0       100          1.2         181.0
and Vanzwol (2012)

Soudki, El-Sayed,         1.0       100          1.2         163.8
and Vanzwol (2012)

Soudki, El-Sayed,         1.0       100          1.2         206.9
and Vanzwol (2012)

Soudki, El-Sayed,         1.0       100          1.2         173.7
and Vanzwol (2012)

Soudki, El-Sayed,         1.0       100          1.2         192.9
and Vanzwol (2012)

Ebead and Marzouk        0.35        --           --          250
(2004)

Ebead and Marzouk        0.35       300          1.2          361
(2004)

Ebead and Marzouk         0.5        --           --          330
(2004)

Ebead and Marzouk         0.5       300          1.2          450
(2004)

Sharaf, Soudki, and       1.2       100          1.2          421
Van Dusen (2006)

Sharaf, Soudki, and       1.2       100          1.2          445
Van Dusen (2006)

Sharaf, Soudki, and       1.2       100          1.2          451
Van Dusen (2006)

Sharaf, Soudki, and       1.2       100          1.2          483
Van Dusen (2006)

Sharaf, Soudki, and       1.2       100          1.2          489
Van Dusen (2006)

Sharaf, Soudki, and       1.2       100          1.2          477
Van Dusen (2006)

Bonding GFRP
laminates

Chen and Li (2005)       1.31        --           --         103.9

Chen and Li (2005)       1.31       800          1.31         148

Chen and Li (2005)       1.31       800          1.31        202.1

Chen and Li (2005)       1.31        --           --         123.8

Chen and Li (2005)       1.31       800          1.31         180

Chen and Li (2005)       1.31       800          1.31        218.8

Chen and Li (2005)       0.59        --           --         146.1

Chen and Li (2005)       0.59       800          1.31        189.6

Bonding GFRP
laminates

Chen and Li (2005)       0.59       800          1.31        289.4

Chen and Li (2005)       0.59       800          1.31        224.2

Chen and Li (2005)       0.59        --           --         225.7

Chen and Li (2005)       0.59       800          1.31        263.9

Prestressed sheet

Kim et al. (2010)        1.44       150         0.165         376

Kim et al. (2010)        1.44       150         0.165         443

Kim et al. (2010)        1.44       150         0.165         392

Prestressed plates

Abdullah, Bailey,         --        100          1.2          284
and Wu (2013)

Abdullah, Bailey,         --        100          1.2         220.2
and Wu (2013)

Abdullah, Bailey,         --        100          1.2          240
and Wu (2013)

Abdullah, Bailey,         --        100          1.2          307
and Wu (2013)

                          [P.sub.u]/     [[DELTA]      Strain
                         [P.sub.u-con     .sub.u]
                             trol]                      [mu]
Author                                      mm       [epsilon]

Bonding CFRP sheets

Harajli and Soudki             1            20           --
(2003)

Harajli and Soudki           0.96           10          1250
(2003)

Harajli and Soudki           1.33           12          2450
(2003)

Harajli and Soudki           1.30           11           --
(2003)

Harajli and Soudki             1            16           --
(2003)

Harajli and Soudki           1.16            9          900
(2003)

Harajli and Soudki           1.28            8          1250
(2003)

Harajli and Soudki           1.32           10          950
(2003)

Harajli and Soudki             1           11.8          --
(2003)

Harajli and Soudki           1.45            8          1180
(2003)

Harajli and Soudki           1.32            8          1000
(2003)

Harajli and Soudki           1.36           11          800
(2003)

Harajli and Soudki             1             8           --
(2003)

Harajli and Soudki           1.17           10          1200
(2003)

Harajli and Soudki           0.97            9          1400
(2003)

Harajli and Soudki           1.01          11.5         750
(2003)

El-Salakawy, Soudki,           1            17           --
and Polak (2004)

Bonding CFRP sheets

El-Salakawy, Soudki,         1.008          15          4000
and Polak (2004)

Bonding GFRP sheets

El-Salakawy, Soudki,         1.04           15          6000
and Polak (2004)

El-Salakawy, Soudki,          100           16           --
and Polak (2004)

El-Salakawy, Soudki,         1.23           20
and Polak (2004)

Bonding CFRP
laminates

Soudki, El-Sayed,              1           14.4          --
and Vanzwol (2012)

Soudki, El-Sayed,            1.12          10.3         3062
and Vanzwol (2012)

Soudki, El-Sayed,            1.02           8.1         2811
and Vanzwol (2012)

Soudki, El-Sayed,            1.29          10.7         3554
and Vanzwol (2012)

Soudki, El-Sayed,            1.08           9.0         2851
and Vanzwol (2012)

Soudki, El-Sayed,            1.20           8.9         2894
and Vanzwol (2012)

Ebead and Marzouk              1           42.01         --
(2004)

Ebead and Marzouk            1.44          18.08         --
(2004)

Ebead and Marzouk              1           35.57         --
(2004)

Ebead and Marzouk            1.36          21.0          --
(2004)

Sharaf, Soudki, and            1           16.40         --
Van Dusen (2006)

Sharaf, Soudki, and          1.06          11.45         --
Van Dusen (2006)

Sharaf, Soudki, and          1.07          13.50         --
Van Dusen (2006)

Sharaf, Soudki, and          1.14          11.50         --
Van Dusen (2006)

Sharaf, Soudki, and          1.16          18.60         --
Van Dusen (2006)

Sharaf, Soudki, and          1.13          11.95        5000
Van Dusen (2006)

Bonding GFRP
laminates

Chen and Li (2005)             1            22           --

Chen and Li (2005)           1.42           12           --

Chen and Li (2005)           1.95            7           --

Chen and Li (2005)            --            30           --

Chen and Li (2005)           1.45           10           --

Chen and Li (2005)           1.77           15           --

Chen and Li (2005)            --             9           --

Chen and Li (2005)            30             7           --

Bonding GFRP
laminates

Chen and Li (2005)            28             7           --

Chen and Li (2005)            54             7           --

Chen and Li (2005)            --            10           --

Chen and Li (2005)            17             6           --

Prestressed sheet

Kim et al. (2010)              1            24           --

Kim et al. (2010)            1.18          25.3          --

Kim et al. (2010)            1.04          22.9          --

Prestressed plates

Abdullah, Bailey,              1           27.3          --
and Wu (2013)

Abdullah, Bailey,            0.78          16.3         3900
and Wu (2013)

Abdullah, Bailey,            0.84          15.2         3800
and Wu (2013)

Abdullah, Bailey,            1.08          14.8         3000
and Wu (2013)

                           Failure
Author                      mode

Bonding CFRP sheets

Harajli and Soudki        Flexural
(2003)

Harajli and Soudki       Flex punch
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki       Flex punch
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

Harajli and Soudki        Punching
(2003)

El-Salakawy, Soudki,      Punching
and Polak (2004)

Bonding CFRP sheets

El-Salakawy, Soudki,      Punching
and Polak (2004)

Bonding GFRP sheets

El-Salakawy, Soudki,      Punching
and Polak (2004)

El-Salakawy, Soudki,      Punching
and Polak (2004)

El-Salakawy, Soudki,      Punching
and Polak (2004)

Bonding CFRP
laminates

Soudki, El-Sayed,         Punching
and Vanzwol (2012)

Soudki, El-Sayed,         Punching
and Vanzwol (2012)

Soudki, El-Sayed,         Punching
and Vanzwol (2012)

Soudki, El-Sayed,         Punching
and Vanzwol (2012)

Soudki, El-Sayed,         Punching
and Vanzwol (2012)

Soudki, El-Sayed,         Punching
and Vanzwol (2012)

Ebead and Marzouk         Flexural
(2004)

Ebead and Marzouk         Flexural
(2004)

Ebead and Marzouk         Flexural
(2004)

Ebead and Marzouk         Flexural
(2004)

Sharaf, Soudki, and       Punching
Van Dusen (2006)

Sharaf, Soudki, and       Punching
Van Dusen (2006)

Sharaf, Soudki, and       Punching
Van Dusen (2006)

Sharaf, Soudki, and       Punching
Van Dusen (2006)

Sharaf, Soudki, and       Punching
Van Dusen (2006)

Sharaf, Soudki, and       Punching
Van Dusen (2006)

Bonding GFRP
laminates

Chen and Li (2005)        Flexural

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Bonding GFRP
laminates

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Chen and Li (2005)        Punching

Prestressed sheet

Kim et al. (2010)         Punching

Kim et al. (2010)         Punching

Kim et al. (2010)         Punching

Prestressed plates

Abdullah, Bailey,         Flexural-
and Wu (2013)             Punching

Abdullah, Bailey,         Punching
and Wu (2013)

Abdullah, Bailey,         Punching
and Wu (2013)

Abdullah, Bailey,         Punching
and Wu (2013)

Notes: where, B, L, h width, length and thickness of the slab,
respectively; b and l are width and length of the column,
respectively; [rho]s the flexural reinforcement ratio,
[b.sub.f] and [t.sub.f] is the width and thickness of FRP,
respectively; [P.sub.u] is the failure load and
[[DELTA].sub.u] s the ultimate deflection.

Table 2. Direct shear strengthening method (Punching strengthening).

                                       B      L      h     d      b

Author                    Specimen     mm     mm    mm     mm    mm

CFRP bars

Meisami,                   CS40-2     1200   1200   85    80.5   150
Mostofinejad, and
Nakamura (2013)

Meisami,                    FR2-8     1200   1200   85    80.5   150
Mostofinejad, and
Nakamura (2013)

Meisami,                   CS40-3     1200   1200   105   74.1   150
Mostofinejad, and
Nakamura (2013)

Meisami,                    FR3-8     1200   1200   105   74.1   150
Mostofinejad, and
Nakamura (2013)

Meisami,                   FR3-24     1200   1200   105   74.1   150
Mostofinejad, and
Nakamura (2013)

CFRP grids

Meisami,                    CS40      1200   1200   105   74.1   150
Mostofinejad, and
Nakamura (2014)

Meisami,                    FG-8A     1200   1200   105   74.1   150
Mostofinejad, and
Nakamura (2014)

Meisami,                   FG-16B     1200   1200   105   74.1   150
Mostofinejad, and
Nakamura (2014)

Meisami,                   FG-16A     1200   1200   105   74.1   150
Mostofinejad, and
Nakamura (2014)

Meisami,                   FG-24A     1200   1200   105   74.1   150
Mostofinejad, and
Nakamura (2014)

GFRP shear bolts

Lawlerand Polak              SB1      1800   1800   120    89    150
(2011)

Lawlerand Polak              SN1      1800   1800   120    89    150
(2011)

Lawlerand Polak              SN2      1800   1800   120    89    150
(2011)

Lawlerand Polak              SN3      1800   1800   120    89    150
(2011)

Lawlerand Polak              SN4      1800   1800   120    89    150
(2011)

External FRP
stirrups

Binici and Bayrak          Control    2133   2133   152   116    304
(2003)

Binici and Bayrak           A4-1      2133   2133   152   116    304
(2003)

Binici and Bayrak           A4-2      2133   2133   152   116    304
(2003)

Binici and Bayrak            A6       2133   2133   152   116    304
(2003)

Binici and Bayrak            A8       2133   2133   152   116    304
(2003)

External FRP
stirrups

Erdogan, Zohrevand,          LC       2130   2130   150   110    300
and Mirmiran (2013)

Erdogan, Zohrevand,         LF-R      2130   2130   150   110    300
and Mirmiran (2013)

Erdogan, Zohrevand,          LS       2130   2130   150   110    300
and Mirmiran (2013)

Erdogan, Zohrevand,          NC       2130   2130   150   110    300
and Mirmiran (2013)

Erdogan, Zohrevand,         NF-R      2130   2130   150   110    300
and Mirmiran (2013)

Erdogan, Zohrevand,          N-S      2130   2130   150   110    300
and Mirmiran (2013)

Erdogan, Zohrevand,         ND-R      2130   2130   150   110    300
and Mirmiran (2013)

Sissakis and Sheikh       Control1    1500   1500   150   120    200
(2007)

Sissakis and Sheikh          A4       1500   1500   150   120    200
(2007)

Sissakis and Sheikh       Control2    1500   1500   150   120    200
(2007)

Sissakis and Sheikh          A3'      1500   1500   150   120    200
(2007)

Sissakis and Sheikh          B3'      1500   1500   150   120    200
(2007)

Sissakis and Sheikh          B4'      1500   1500   150   120    200
(2007)

Sissakis and Sheikh          C3'      1500   1500   150   120    200
(2007)

Sissakis and Sheikh          C4'      1500   1500   150   120    200
(2007)

Sissakis and Sheikh          D3'      1500   1500   150   120    200
(2007)

Sissakisand Sheikh           D4'      1500   1500   150   120    200
(2007)

Sissakis and Sheikh       Control3    1500   1500   150   120    200
(2007)

Sissakis and Sheikh          A3       1500   1500   150   120    200
(2007)

External FRP
stirrups

Sissakis and Sheikh          A5       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          B3       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          B5       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          C3       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          C5       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          D3       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          D5       1500   1500   150   120    200
(2007)

Sissakis and Sheikh       Control4    1500   1500   150   120    200
(2007)

Sissakis and Sheikh          A4       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          A6       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          B4       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          B6       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          C4       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          C6       1500   1500   150   120    200
(2007)

Sissakis and Sheikh          D4       1500   1500   150   120    200
(2007)

Sissakisand Sheikh           D6       1500   1500   150   120    200
(2007)

Erdogan, Binici, and       Control    2000   2000   150   120    150
Ozcebe (2010)

Erdogan, Binici, and         IP3      2000   2000   150   120    150
Ozcebe (2010)

Erdogan, Binici, and         IP4      2000   2000   150   120    150
Ozcebe (2010)

Erdogan, Binici, and         IP5      2000   2000   150   120    150
Ozcebe (2010)

Erdogan, Binici, and         CWS      2000   2000   150   120    150
Ozcebe (2010)

Erdogan, Binici, and        CWOS      2000   2000   150   120    150
Ozcebe (2010)

Erdogan, Binici, and         R1       2000   2000   150   120    250
Ozcebe (2011)

Erdogan, Binici, and       S1-120     2000   2000   150   120    250
Ozcebe (2011)

Erdogan, Binici, and         R2       2000   2000   150   120    167
Ozcebe (2011)

Erdogan, Binici, and       S2-120     2000   2000   150   120    167
Ozcebe (2011)

Erdogan, Binici, and       S2-180     2000   2000   150   120    167
Ozcebe (2011)

Erdogan, Binici, and         R3       2000   2000   150   120    125
Ozcebe (2011)

Erdogan, Binici, and       S3-180     2000   2000   150   120    125
Ozcebe (2011)

Meisami,                   Control    1200   1200   105   74.1   200
Mostofinejad, and
Nakamura (2015)

Meisami,                    FF3-8     1200   1200   105   74.1   200
Mostofinejad, and
Nakamura (2015)

Meisami,                   FF3-16     1200   1200   105   74.1   200
Mostofinejad, and
Nakamura (2015)

Meisami,                   FF3-24     1200   1200   105   74.1   200
Mostofinejad, and
Nakamura (2015)

Rodrigues, Silva,          Control    1000   1000   60     47    85
and Oliveira (2015)

Rodrigues, Silva,            L3       1000   1000   60     47    85
and Oliveira (2015)

Rodrigues, Silva,            L4       1000   1000   60     47    85
and Oliveira (2015)

Rodrigues, Silva,           Lrad      1000   1000   60     47    85
and Oliveira (2015)

                          l    [rho]   [f.sub.y]    [f'.sub.c]

                                                         N/
Author                    mm      %       N/mmm2         mm2

CFRP bars

Meisami,                  150    1.1       345          41.4
Mostofinejad, and
Nakamura (2013)

Meisami,                  150    1.1       345          36.6
Mostofinejad, and
Nakamura (2013)

Meisami,                  150    2.2       420          42.4
Mostofinejad, and
Nakamura (2013)

Meisami,                  150    2.2       420          43.5
Mostofinejad, and
Nakamura (2013)

Meisami,                  150    2.2       420          43.5
Mostofinejad, and
Nakamura (2013)

CFRP grids

Meisami,                  150    2.2       420          42.4
Mostofinejad, and
Nakamura (2014)

Meisami,                  150    2.2       420          43.5
Mostofinejad, and
Nakamura (2014)

Meisami,                  150    2.2       420          43.5
Mostofinejad, and
Nakamura (2014)

Meisami,                  150    22        420          44.1
Mostofinejad, and
Nakamura (2014)

Meisami,                  150    2.2       420          41.7
Mostofinejad, and
Nakamura (2014)

GFRP shear bolts

Lawlerand Polak           150   0.88        --           44
(2011)

Lawlerand Polak           150   0.88        --           36
(2011)

Lawlerand Polak           150   0.88        --           36
(2011)

Lawlerand Polak           150   0.88        --           36
(2011)

Lawlerand Polak           150   0.88        --           36
(2011)

External FRP
stirrups

Binici and Bayrak         304   1.76       448          28.3
(2003)

Binici and Bayrak         304   1.76       448          28.3
(2003)

Binici and Bayrak         304   1.76       448          28.3
(2003)

Binici and Bayrak         304   1.76       448          28.3
(2003)

Binici and Bayrak         304   1.76       448          28.3
(2003)

External FRP
stirrups

Erdogan, Zohrevand,       300   1.86       464          15.6
and Mirmiran (2013)

Erdogan, Zohrevand,       300   1.86       464          15.6
and Mirmiran (2013)

Erdogan, Zohrevand,       300   1.86       464          15.6
and Mirmiran (2013)

Erdogan, Zohrevand,       300   1.86       464          32.3
and Mirmiran (2013)

Erdogan, Zohrevand,       300   1.86       464          32.3
and Mirmiran (2013)

Erdogan, Zohrevand,       300   1.86       464          32.3
and Mirmiran (2013)

Erdogan, Zohrevand,       300   1.86       464          32.3
and Mirmiran (2013)

Sissakis and Sheikh       200   1.49       428          42.6
(2007)

Sissakis and Sheikh       200   1.49       428          42.6
(2007)

Sissakis and Sheikh       200   1.49       428          36.1
(2007)

Sissakis and Sheikh       200   1.49       428          36.1
(2007)

Sissakis and Sheikh       200   1.49       428          36.1
(2007)

Sissakis and Sheikh       200   1.49       428          36.1
(2007)

Sissakis and Sheikh       200   1.49       428          36.1
(2007)

Sissakis and Sheikh       200   1.49       428          36.1
(2007)

Sissakis and Sheikh       200   1.49       428          36.1
(2007)

Sissakisand Sheikh        200   1.49       428          36.1
(2007)

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

External FRP
stirrups

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

Sissakis and Sheikh       200   2.23       480          34.5
(2007)

Sissakis and Sheikh       200   2.23       480          26.6
(2007)

Sissakis and Sheikh       200   2.23       480          26.6
(2007)

Sissakis and Sheikh       200   2.23       480          26.6
(2007)

Sissakis and Sheikh       200   2.23       480          26.6
(2007)

Sissakis and Sheikh       200   2.23       480          26.6
(2007)

Sissakis and Sheikh       200   2.23       480          26.6
(2007)

Sissakis and Sheikh       200   2.23       480          26.6
(2007)

Sissakis and Sheikh       200   2.23       480          26.6
(2007)

Sissakisand Sheikh        200   2.23       480          26.6
(2007)

Erdogan, Binici, and      120              448           35
Ozcebe (2010)

Erdogan, Binici, and      120              448           33
Ozcebe (2010)

Erdogan, Binici, and      120              448           26
Ozcebe (2010)

Erdogan, Binici, and      120              448           31
Ozcebe (2010)

Erdogan, Binici, and      150              448           30
Ozcebe (2010)

Erdogan, Binici, and      120              448           31
Ozcebe (2010)

Erdogan, Binici, and      250    1.5       448           32
Ozcebe (2011)

Erdogan, Binici, and      250    1.5       448           31
Ozcebe (2011)

Erdogan, Binici, and      333    1.5       448           29
Ozcebe (2011)

Erdogan, Binici, and      333    1.5       448           33
Ozcebe (2011)

Erdogan, Binici, and      333    1.5       448           30
Ozcebe (2011)

Erdogan, Binici, and      375    1.5       448           30
Ozcebe (2011)

Erdogan, Binici, and      375    1.5       448           30
Ozcebe (2011)

Meisami,                  200    2.2       420          42.4
Mostofinejad, and
Nakamura (2015)

Meisami,                  200    2.2       420          44.8
Mostofinejad, and
Nakamura (2015)

Meisami,                  200    2.2       420          44.8
Mostofinejad, and
Nakamura (2015)

Meisami,                  200    2.2       420          44.8
Mostofinejad, and
Nakamura (2015)

Rodrigues, Silva,         85    1.07        --           40
and Oliveira (2015)

Rodrigues, Silva,         85    1.07        --           40
and Oliveira (2015)

Rodrigues, Silva,         85    1.07        --           40
and Oliveira (2015)

Rodrigues, Silva,         85    1.07        --           40
and Oliveira (2015)

                                  [A.sub.f/            s/d
                                  perimeter]

Author                            [mm.sup.2]

CFRP bars

Meisami,                              --                --
Mostofinejad, and
Nakamura (2013)

Meisami,                             452               0.50
Mostofinejad, and
Nakamura (2013)

Meisami,                              --                --
Mostofinejad, and
Nakamura (2013)

Meisami,                             452               0.50
Mostofinejad, and
Nakamura (2013)

Meisami,                             904               0.50
Mostofinejad, and
Nakamura (2013)

CFRP grids

Meisami,                              --                --
Mostofinejad, and
Nakamura (2014)

Meisami,                             294               0.50
Mostofinejad, and
Nakamura (2014)

Meisami,                             588               0.50
Mostofinejad, and
Nakamura (2014)

Meisami,                             588               0.50
Mostofinejad, and
Nakamura (2014)

Meisami,                             588               0.50
Mostofinejad, and
Nakamura (2014)

GFRP shear bolts

Lawlerand Polak                       --                --
(2011)

Lawlerand Polak                      981               0.80
(2011)

Lawlerand Polak                      904               0.80
(2011)

Lawlerand Polak                      904               0.80
(2011)

Lawlerand Polak                      904               0.80
(2011)

External FRP
stirrups

Binici and Bayrak                     --                --
(2003)

Binici and Bayrak                   812.4              0.50
(2003)

Binici and Bayrak                   406.4              0.50
(2003)

Binici and Bayrak                   812.8              0.50
(2003)

Binici and Bayrak                   812.8              0.50
(2003)

External FRP
stirrups

Erdogan, Zohrevand,                   --                --
and Mirmiran (2013)

Erdogan, Zohrevand,        76.5/127.5/76.5/127.5/7     0.50
and Mirmiran (2013)          6.5/127.5/76.5/127.5

Erdogan, Zohrevand,        76.5/127.5/76.5/127.5/7     0.50
and Mirmiran (2013)          6.5/127.5/76.5/127.5

Erdogan, Zohrevand,                   --                --
and Mirmiran (2013)

Erdogan, Zohrevand,        76.5/127.5/76.5/127.5/7     0.50
and Mirmiran (2013)          6.5/127.5/76.5/127.5

Erdogan, Zohrevand,        76.5/127.5/76.5/127.5/7     0.50
and Mirmiran (2013)          6.5/127.5/76.5/127.5

Erdogan, Zohrevand,        76.5/127.5/76.5/127.5/7     0.50
and Mirmiran (2013)          6.5/127.5/76.5/127.5

Sissakis and Sheikh                   --                --
(2007)

Sissakis and Sheikh                  814               0.50
(2007)

Sissakis and Sheikh                   --                --
(2007)

Sissakis and Sheikh              506/1012/506          0.75
(2007)

Sissakis and Sheikh                  748               0.75
(2007)

Sissakis and Sheikh                  748               0.50
(2007)

Sissakis and Sheikh                  924               0.75
(2007)

Sissakis and Sheikh                  924               0.50
(2007)

Sissakis and Sheikh                  924               0.75
(2007)

Sissakisand Sheikh                   924               0.50
(2007)

Sissakis and Sheikh                   --                --
(2007)

Sissakis and Sheikh              462/924/462           0.50
(2007)

External FRP
stirrups

Sissakis and Sheikh              858/858/660           0.50
(2007)                            /1320/660

Sissakis and Sheikh                  616               0.50
(2007)

Sissakis and Sheikh                  792               0.50
(2007)

Sissakis and Sheikh                  792               0.50
(2007)

Sissakis and Sheikh                  1188              0.50
(2007)

Sissakis and Sheikh                  792               0.50
(2007)

Sissakis and Sheikh                  792               0.50
(2007)

Sissakis and Sheikh                  1280              0.50
(2007)

Sissakis and Sheikh                  2234              0.50
(2007)

Sissakis and Sheikh                  2912              0.50
(2007)

Sissakis and Sheikh                  2356              0.50
(2007)

Sissakis and Sheikh                  3035              0.50
(2007)

Sissakis and Sheikh                  2960              0.50
(2007)

Sissakis and Sheikh                  3920              0.50
(2007)

Sissakis and Sheikh                  2960              0.50
(2007)

Sissakisand Sheikh                   3920              0.50
(2007)

Erdogan, Binici, and                  --                --
Ozcebe (2010)

Erdogan, Binici, and                158.4              0.50
Ozcebe (2010)

Erdogan, Binici, and                158.4              0.50
Ozcebe (2010)

Erdogan, Binici, and                158.4              0.50
Ozcebe (2010)

Erdogan, Binici, and                237.6              0.50
Ozcebe (2010)

Erdogan, Binici, and                 19.8              0.50
Ozcebe (2010)

Erdogan, Binici, and                  --                --
Ozcebe (2011)

Erdogan, Binici, and                158.4              0.50
Ozcebe (2011)

Erdogan, Binici, and                  --                --
Ozcebe (2011)

Erdogan, Binici, and                158.4              0.50
Ozcebe (2011)

Erdogan, Binici, and                237.6              0.50
Ozcebe (2011)

Erdogan, Binici, and                  --                --
Ozcebe (2011)

Erdogan, Binici, and                237.6              0.50
Ozcebe (2011)

Meisami,                              --               0.50
Mostofinejad, and
Nakamura (2015)

Meisami,                             50.4              0.50
Mostofinejad, and
Nakamura (2015)

Meisami,                            100.8              0.50
Mostofinejad, and
Nakamura (2015)

Meisami,                            100.8              0.50
Mostofinejad, and
Nakamura (2015)

Rodrigues, Silva,                     --                --
and Oliveira (2015)

Rodrigues, Silva,                   103.7              0.5
and Oliveira (2015)

Rodrigues, Silva,                   103.7              0.5
and Oliveira (2015)

Rodrigues, Silva,                   155.5              0.5
and Oliveira (2015)

                          [No.sub     [P.sub.u]         Pu/
                           .holes]                 [P.sub.u-con
                                                       trol]
Author                                    kN

CFRP bars

Meisami,                     --         224.1           --
Mostofinejad, and
Nakamura (2013)

Meisami,                      8          248           1.11
Mostofinejad, and
Nakamura (2013)

Meisami,                     --         240.4            1
Mostofinejad, and
Nakamura (2013)

Meisami,                      8         286.2          1.19
Mostofinejad, and
Nakamura (2013)

Meisami,                     24          412           1.71
Mostofinejad, and
Nakamura (2013)

CFRP grids

Meisami,                     --         241.7            1
Mostofinejad, and
Nakamura (2014)

Meisami,                      8         313.8          1.29
Mostofinejad, and
Nakamura (2014)

Meisami,                     16         302.3          1.25
Mostofinejad, and
Nakamura (2014)

Meisami,                     16         347.6          1.44
Mostofinejad, and
Nakamura (2014)

Meisami,                     24          375           1.55
Mostofinejad, and
Nakamura (2014)

GFRP shear bolts

Lawlerand Polak              --          253             1
(2011)

Lawlerand Polak              32          199           0.79
(2011)

Lawlerand Polak              32          278            1.1
(2011)

Lawlerand Polak              32          310           1.23
(2011)

Lawlerand Polak              32          332           1.31
(2011)

External FRP
stirrups

Binici and Bayrak            24          494             1
(2003)

Binici and Bayrak            24          595           1.20
(2003)

Binici and Bayrak            24          668           1.35
(2003)

Binici and Bayrak            24          721           1.45
(2003)

Binici and Bayrak            32          744           1.50
(2003)

External FRP
stirrups

Erdogan, Zohrevand,          --          401             1
and Mirmiran (2013)

Erdogan, Zohrevand,          64          465           1.16
and Mirmiran (2013)

Erdogan, Zohrevand,          64          696           1.73
and Mirmiran (2013)

Erdogan, Zohrevand,          64          547             1
and Mirmiran (2013)

Erdogan, Zohrevand,          64          683           1.25
and Mirmiran (2013)

Erdogan, Zohrevand,          64          750           1.37
and Mirmiran (2013)

Erdogan, Zohrevand,          64          940           1.71
and Mirmiran (2013)

Sissakis and Sheikh          --          575             1
(2007)

Sissakis and Sheikh          16          632           1.10
(2007)

Sissakis and Sheikh          --          439             1
(2007)

Sissakis and Sheikh          12          591           1.35
(2007)

Sissakis and Sheikh          24          659           1.50
(2007)

Sissakis and Sheikh          32          638           1.45
(2007)

Sissakis and Sheikh          24          612           1.39
(2007)

Sissakis and Sheikh          32          673           1.53
(2007)

Sissakis and Sheikh          12          550           1.25
(2007)

Sissakisand Sheikh           16          605           1.38
(2007)

Sissakis and Sheikh          --          476             1
(2007)

Sissakis and Sheikh          12          646           1.36
(2007)

External FRP
stirrups

Sissakis and Sheikh          20          671           1.41
(2007)

Sissakis and Sheikh          24          744           1.56
(2007)

Sissakis and Sheikh          40          791           1.66
(2007)

Sissakis and Sheikh          24          775           1.63
(2007)

Sissakis and Sheikh          40          858           1.80
(2007)

Sissakis and Sheikh          12          616           1.29
(2007)

Sissakis and Sheikh          20          617           1.30
(2007)

Sissakis and Sheikh          --          479             1
(2007)

Sissakis and Sheikh          16          595           1.24
(2007)

Sissakis and Sheikh          24          631           1.32
(2007)

Sissakis and Sheikh          32          701           1.46
(2007)

Sissakis and Sheikh          48          791           1.65
(2007)

Sissakis and Sheikh          32          781           1.63
(2007)

Sissakis and Sheikh          48          872           1.82
(2007)

Sissakis and Sheikh          16          634           1.32
(2007)

Sissakisand Sheikh           24          617           1.33
(2007)

Erdogan, Binici, and         --          500             1
Ozcebe (2010)

Erdogan, Binici, and         24          601           1.20
Ozcebe (2010)

Erdogan, Binici, and         32          571           1.14
Ozcebe (2010)

Erdogan, Binici, and         40          657           1.31
Ozcebe (2010)

Erdogan, Binici, and         28          592           1.18
Ozcebe (2010)

Erdogan, Binici, and         28          594           1.19
Ozcebe (2010)

Erdogan, Binici, and         --          500             1
Ozcebe (2011)

Erdogan, Binici, and         24          657           1.31
Ozcebe (2011)

Erdogan, Binici, and         --          423             1
Ozcebe (2011)

Erdogan, Binici, and         24          649           1.53
Ozcebe (2011)

Erdogan, Binici, and         24          571           1.35
Ozcebe (2011)

Erdogan, Binici, and         --          414             1
Ozcebe (2011)

Erdogan, Binici, and         24          564           1.36
Ozcebe (2011)

Meisami,                     --         241.7            1
Mostofinejad, and
Nakamura (2015)

Meisami,                      8         331.2          1.37
Mostofinejad, and
Nakamura (2015)

Meisami,                     16         428.5          1.77
Mostofinejad, and
Nakamura (2015)

Meisami,                     24         475.1          1.97
Mostofinejad, and
Nakamura (2015)

Rodrigues, Silva,            --           71             1
and Oliveira (2015)

Rodrigues, Silva,            24          105           1.48
and Oliveira (2015)

Rodrigues, Silva,            32          125           1.76
and Oliveira (2015)

Rodrigues, Silva,            48          112           1.58
and Oliveira (2015)

                          [[DELTA]
                           .sub.u]
                                              Failure
Author                       mm                mode

CFRP bars

Meisami,                                     Punching
Mostofinejad, and
Nakamura (2013)

Meisami,                    15.1             Punching
Mostofinejad, and
Nakamura (2013)

Meisami,                     6.4             Punching
Mostofinejad, and
Nakamura (2013)

Meisami,                     8.9             Punching
Mostofinejad, and
Nakamura (2013)

Meisami,                    29.3             Flexural
Mostofinejad, and
Nakamura (2013)

CFRP grids

Meisami,                     7.3             Punching
Mostofinejad, and
Nakamura (2014)

Meisami,                    10.1             Punching
Mostofinejad, and
Nakamura (2014)

Meisami,                     8.4             Punching
Mostofinejad, and
Nakamura (2014)

Meisami,                     8.5         Punching-flexural
Mostofinejad, and
Nakamura (2014)

Meisami,                     10              flexural
Mostofinejad, and
Nakamura (2014)

GFRP shear bolts

Lawlerand Polak                                Shear
(2011)

Lawlerand Polak              22              Flexural
(2011)

Lawlerand Polak              39              Flexural
(2011)

Lawlerand Polak              40              Flexural
(2011)

Lawlerand Polak              37              Flexural
(2011)

External FRP
stirrups

Binici and Bayrak           11.3             Punching
(2003)

Binici and Bayrak           14.6            Punching-in
(2003)

Binici and Bayrak           18.9           Punching-out
(2003)

Binici and Bayrak           19.8           Punching-out
(2003)

Binici and Bayrak           20.7           Punching-out
(2003)

External FRP
stirrups

Erdogan, Zohrevand,         12.9             Punching
and Mirmiran (2013)

Erdogan, Zohrevand,         31.8           Punching-out
and Mirmiran (2013)

Erdogan, Zohrevand,         22.4            Punching-in
and Mirmiran (2013)

Erdogan, Zohrevand,         13.5             Punching
and Mirmiran (2013)

Erdogan, Zohrevand,         33.9           Punching-out
and Mirmiran (2013)

Erdogan, Zohrevand,         36.5           Punching-out
and Mirmiran (2013)

Erdogan, Zohrevand,         19.7           Punching-out
and Mirmiran (2013)

Sissakis and Sheikh          13              Punching
(2007)

Sissakis and Sheikh                        Punching-out
(2007)

Sissakis and Sheikh          10              Punching
(2007)

Sissakis and Sheikh          11            Punching-out
(2007)

Sissakis and Sheikh          16             Punching-in
(2007)

Sissakis and Sheikh          15            Punching-out
(2007)

Sissakis and Sheikh          11             Punching-in
(2007)

Sissakis and Sheikh          16            Punching-out
(2007)

Sissakis and Sheikh          11             Punching-in
(2007)

Sissakisand Sheikh           15            Punching-out
(2007)

Sissakis and Sheikh          7.5             Punching
(2007)

Sissakis and Sheikh          12             Punching-in
(2007)

External FRP
stirrups

Sissakis and Sheikh          13            Punching-out
(2007)

Sissakis and Sheikh         11.5           Punching-out
(2007)

Sissakis and Sheikh          15            Punching-out
(2007)

Sissakis and Sheikh          12            Punching-out
(2007)

Sissakis and Sheikh          19             Punching-in
(2007)

Sissakis and Sheikh          12             Punching-in
(2007)

Sissakis and Sheikh          10             Punching-in
(2007)

Sissakis and Sheikh          7.5             Punching
(2007)

Sissakis and Sheikh          10             Punching-in
(2007)

Sissakis and Sheikh          11             Punching-in
(2007)

Sissakis and Sheikh          12            Punching-out
(2007)

Sissakis and Sheikh          30            Punching-out
(2007)

Sissakis and Sheikh          15            Punching-out
(2007)

Sissakis and Sheikh          25            Punching-out
(2007)

Sissakis and Sheikh          11             Punching-in
(2007)

Sissakisand Sheikh           15             Punching-in
(2007)

Erdogan, Binici, and        17.5             Punching
Ozcebe (2010)

Erdogan, Binici, and        35.5           Punching-out
Ozcebe (2010)

Erdogan, Binici, and        35.9           Punching-out-
Ozcebe (2010)

Erdogan, Binici, and        49.1         Punching-out and
Ozcebe (2010)                                flexural

Erdogan, Binici, and        31.8            Punching-in
Ozcebe (2010)

Erdogan, Binici, and        34.2            Punching-in
Ozcebe (2010)

Erdogan, Binici, and        17.5             Punching
Ozcebe (2011)

Erdogan, Binici, and        49.1           Punching-out
Ozcebe (2011)

Erdogan, Binici, and        14.4             Punching
Ozcebe (2011)

Erdogan, Binici, and        35.6            Punching-in
Ozcebe (2011)

Erdogan, Binici, and        33.1            Punching-in
Ozcebe (2011)

Erdogan, Binici, and        13.8             Punching
Ozcebe (2011)

Erdogan, Binici, and        27.8           Punching-out
Ozcebe (2011)

Meisami,                     7.3             Punching
Mostofinejad, and
Nakamura (2015)

Meisami,                     8.6             Punching
Mostofinejad, and
Nakamura (2015)

Meisami,                    14.1         Punching-Flexural
Mostofinejad, and
Nakamura (2015)

Meisami,                    18.2             Flexural
Mostofinejad, and
Nakamura (2015)

Rodrigues, Silva,             9              Punching
and Oliveira (2015)

Rodrigues, Silva,            15        Punching-out-Flexural
and Oliveira (2015)

Rodrigues, Silva,            20        Punching-out-Flexural
and Oliveira (2015)

Rodrigues, Silva,            20        Punching-out-Flexural
and Oliveira (2015)

Notes: where, [f.sub.y] is the yield strength of flexural
reinforcements, [A.sub.f/perimeter] is area of FRB in one
perimeter, s is the spacing of FRP reinforcement, [No.sub.holes]
is the total number of holes in each slab.

Table 3. Comparison between the flexural and punching shear
strengthening methods.

Indirect shear
strengthening method
(Flexural
strengthening)

Merits                   * Many types of FRP can be
                         used such as, sheets and
                         laminates.

                         * No large or noisy plant or
                         equipment used.

                         * Increase the flexural
                         stiffness of the slab.

                         * The use of GFRP laminates
                         demonstrate a higher level of
                         increasing the load capacity
                         of the slab compared with the
                         other type of the flexural
                         strengthening method. The
                         increase was ranged between
                         17%-95%. However, this can be
                         achieved when bonding two
                         layers of GFRP for slab with
                         low concrete compressive
                         strength and reinforcement
                         ratio.

                         * This method can be used when
                         the tensile face of the slab
                         is accessible.

Demerits                 * The effectiveness of this
                         method heavily depends on the
                         surface preparation.
                         Therefore, an extensive
                         surface preparation work are
                         needed such as sand blasting,
                         grinding and all dust,
                         dirt, oi; and any other
                         materials that would affect
                         the bond of FRP to concrete
                         should be removed.

                         * Specialized training
                         required.

                         * Large amount of FRP and
                         epoxy are needed.

                         * Performance of (FRP)
                         materials and FRP bond to
                         concrete can be negatively
                         affected by the environment
                         effects, such as Alkaline,
                         Water and Dry heat exposure
                         (Cromwell, Harries, and
                         Shahrooz 2011).

                         * FRP is not protected from
                         the mechanical damages and
                         aging effects.

                         * The crack patterns in the
                         strengthened specimens could
                         not be clearly seen because of
                         the application of FRP sheets
                         or laminates.

                         * Increasing the area of FRP
                         reinforcement reduces the
                         ductility of the strengthened
                         slab and punching shear mode
                         is governed.

                         * The most common failure mode
                         is due to de-bonding of FRP
                         plate which prevents the FRP
                         reaching to its full tensile
                         strength.

Direct shear strengthening method (Punching shear
strengthening)

Merits                   * It requires no surface
                         preparation work and a minimal
                         installation time after
                         drilling the holes compared to
                         the flexural strengthening
                         method.

                         * It requires less epoxy
                         consumption compared to the
                         flexural strengthening method.

                         * This method has superior
                         bond characteristics compared
                         to flexural strengthening
                         method.

                         * Usability reduces the
                         probability of deterioration
                         of FRP that results from the
                         environment effect and
                         mechanical damage.

                         * Usability to significantly
                         reduce the probability of harm
                         resulting from acts of
                         vandalism, mechanical damages
                         and aging effect.

                         * The debonding failure that
                         is associated with the
                         flexural strengthening method
                         is completely absent in this
                         method.

                         * It shows a substantial
                         increase in shear capacity and
                         ductility of the slab, which
                         is very important in
                         earthquake prone regions.

                         * Increasing area of FRP
                         increases the shear capacity
                         and the strengthened slab
                         fails in flexural mode with
                         higher deformation compared to
                         the unstrengthened slab.

                         * The use of FRP fan
                         demonstrates a high level of
                         increasing the load capacity
                         of the slab compared with the
                         other type of the punching
                         strengthening method. The
                         increase in the load capacity
                         of the strengthened slab
                         reached up to 97%.

Demerits                 * Noisy equipment used for
                         drilling holes.

                         * Drilling a large number of
                         holes with close spacing
                         through the slab thickness may
                         result in cutting the existing
                         steel reinforcements.

                         * Drilling with a high
                         accuracy without any slope is
                         required to avoid damage the
                         existing shear reinforcements.

                         * FRP fan and external FRP
                         stirrups can be used only if
                         the top and bottom face of the
                         slab are accessible
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Article Details
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Author:Saleh, Haifa; Abdouka, Kamiran; Mahaidi, Riadh Al-; Kalfat, Robin
Publication:Australian Journal of Structural Engineering
Date:Jul 1, 2018
Words:14553
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