Research on the use of FRP in concrete structures began in Europe in the 1960’s [44, 55, 14] , but pioneering work took place in the 1980’s in Switzerland and resulted in successful practical applications [30, 31] . Earlier applications of FRP strengthening in Europe were performed in 1991 on the Ibach Bridge, Switzerland; and Kattenbusch Roadway Bridge in Germany  . A pan- European collaborative research (EUROCRETE) was established in 1993 to develop FRP reinforcement for concrete and included partners from the United Kingdom, Switzerland, France, Norway and Netherlands. Near surface Mounted ( NSM) carbon FRP strips were used to rehabilitate the “Tobel Bridge” in Southern Germany in 1999  . In 2000 "Design guidance for strengthening concrete structures using fibre composite materials" was established by the UK Concrete Society  -Technical Report No 55. In 2001 the International Federation for Structural Concrete (FIB) Task Group 9.3 on FRP Reinforcement for Concrete Structures published a bulletin on design and guidelines for externally bonded FRP repair systems [CEB-FIP 2001]  .
necessarily help to enhance the shear capacity of PHC slabs (Yang, 1994). The comparisons of the load-deflection relation curves between the S1-series and the S2-series are shown in Figure 3.22. The load-deflection curves between the control slabs are shown in Figure 3.22(a), which matched well within the elastic range. However, the low-prestressing specimen showed higher shear capacity (291 kN) than the medium-prestressing specimen (280 kN). This is consistent with the literature finding (Yang, 1994) that higher prestrssing level might not necessarily help to enhance the shear capacity of PHC slabs. Because the main function of the prestressing strands at the bottom of PHC slabs are to resist the tensile stress induced by bending, whereas the shear force is mainly carried by the concrete in the middle of each web. According to the data provided by the supplier, S1-sereis and S2-series had different concrete strength (59.3MPa for S1-sereis and 52.2 MPa for S2-series, respectively). It is reasonable that with the higher concrete strength, S1-series showed higher shear capacity than S2-series. In other words, the shear capacity of the non-strengthened PHC slabs highly depends on the tensile strength of the concrete itself.
4.2. Constraining Effect Some experimental researches have shown that coupling beams longitudinally expand under loads in tests [9,10]. However, in real structures, this may not take place because of the constraining effect of slab diaphragm and high rigidity of shear walls. In the present research, the expansions of some specimens were prevented using a longitudinal bar to account for the effect of the slab diaphragm. The longitudinal bar was installed in PVC pipes located at the middle of the specimens and anchored at their two ends using two nuts. To eliminate the spacing between the nuts and the specimens, an initial tensile force was applied to the bar by fixing the nuts. Due to elongation of the specimens during loading, tensile forces were applied to the bar. These forces were recorded by a load cell. Table 3 shows the measured axial loads in the constraint specimens before and during loading. Also, this table presents vertical displacements of one end of the beams related to the other end at maximum shear and axial forces.
the finite element method had been carried out in order to investigate the effect of this additional reinforcement for both normal strength and high strength concrete. The computer program ANSYS-V12.0 has been utilized in the finite element analysis. The obtained results indicate that, the proposed shear reinforcement system has a positive effect in the enhancement of both the punchingshear capacity and the strain energy of interior slab-column connection of both normal and high strength concrete. The general finite element software ANSYS can be used successfully to simulate the punchingshear behaviour of reinforced concrete flat plates. Joaquim A.O. Barros et.al, (2015) presented a new type of carbon-fibre-reinforced-polymer (CFRP) laminate of U-shape is used by adopting a novel hybrid technique for the simultaneous flexural and punching strengthening of existing RC slabs. Besides, this hybrid technique aims to provide a better bond performance for the embedded-through- section (ETS) and near-surface mounted (NSM) CFRPs by improving the anchorage conditions.Moreover,a higher resistance to the susceptibility of occurrence of other premature failure modes, like concrete cover delamination, is offered by using this hybrid technique. A 3D nonlinear finite-element (FR) model is developed to simulate the experimental tests by considering the nonlinear behaviour of the constituent materials. The experimental program and numerical model are described, and the relevant results are analysed. Francisco Natario et.al, (2015) investigated the behaviour of cantilever bridge deck slabs under fatigue loads. A specific experimental programme consisting on eleven tests under concentrated fatigue loads and four static tests (reference specimens) is presented. The results show that cantilever bridge deck slabs are significantly less sensitive to shear –fatigue failures than beams without shear reinforcement. Some slabs failed due to rebar fractures. They presented significant remaining life after first rebar failure occurred and eventually failed due to shear. The test results are finally compared to the shear-fatigue provisions for the fib-Model Code 2010 and the critical shear crack theory to discuss their suitability.
For RC elements repaired with CFRP sheets, the performance and the stiffness is affected by the properties of the adhesive interface layer between the CFRP sheets and the RC structure. Some studies have investigated the effect of the adhesive layer properties on the structural and dynamic properties of the CFRP repaired RC structures. The strength of the bonded adhesive reduces due to both absorption of moisture and an increase in test temperature . Thus, considerable drying may be required to obtain a good bond . In , a method is proposed to estimate the fatigue strength
Structural failures of highway bridge structures are not common under static loading. However, in highway bridges, beam and slab failure usually occur in two common forms, direct flexural and/or punchingshear. The direct flexural failure typically occurs in beam or slab members and is associated with overall bending. This type of failure arises from the formation of diagonal tension cracks in the region of maximum bending moment and extends across the entire width of the member. However, punchingshear failure is a more localised effect associated with thin slabs or two-way slab-column members when subjected to a highly concentrated load. Punchingshear failure occurs when the principal stress across the critical surface of the section exceeds the tensile strength of the concrete due to applied loading and failure occurs with limited warning. An example of this type of complete failure is seen in Figure 1. Failure occurs with the potential diagonal crack following the surface of a truncated cone around the load. The failure surface extends from the bottom of the member diagonally upward to the top surface. For a normal concrete slab, the angle of inclination of the failure surface ranges approximately from 20 to 45 degrees depending on the amount of shear reinforcement . However, very little information on this parameter is available for UHPFRC.
One possibility for strengthening existing ﬂat slabs consists on gluing ﬁbre reinforced polymers (FRPs) at the concrete surface. When applied on top of slab–column connections, this technique allows increasing the ﬂexural stiffness and strength of the slab as well as its punching strength. Nevertheless, the higher punching strength is associated to a reduction on the deformation capacity of the slab–column connec- tion, which can be detrimental for the overall behaviour of the structure (leading to a more brittle behav- iour of the system). Design approaches for this strengthening technique are usually based on empirical formulas calibrated on the basis of the tests performed on isolated test specimens. However, some signif- icant topics as the reduction on the deformation capacity or the inﬂuence of the whole slab (accounting for the reinforcement at mid-span) on the efﬁciency of the strengthening are neglected. In this paper, a critical review of this technique for strengthening against punchingshear is investigated on the basis of the physical model proposed by the Critical Shear Crack Theory (CSCT). This approach allows taking into account the amount, layout and mechanical behaviour of the bonded FRP’s in a consistent manner to estimate the punching strength and deformation capacity of strengthenedslabs. The approach is ﬁrst used to predict the punching strength of available test data, showing a good agreement. Then, it is applied in order to investigate strengthened continuous slabs, considering moment redistribution after concrete cracking and reinforcement yielding. This latter study provides valuable information regarding the differences between the behaviour of isolated test specimens and real strengthened ﬂat slabs. The results show that empirical formulas calibrated on isolated specimens may overestimate the actual performance of FRP’s strengthening. Finally, taking advantage of the physical model of the CSCT, the effect of the construction sequence on the punchingshear strength is also evaluated, revealing the role of this issue which is also neglected in most empirical approaches.
One of the main concerns related to two-way flat slabs is the punchingshear capacity at slab column connection, which is subjected to a very complex three-dimensional stress state. Punchingshear failure is hence characterized by the development of a truncated cone shaped surface at the slab-column connection. Punchingshear can thus result from a concentrated load or reaction acting on a relatively small area, called the loaded area, of a slab or a foundation. This type of failure is usually both brittle and catastrophic since it may generate the global collapse of the structure due to the increasing load transfer to neighboring columns and to the slabs located underneath. The load carrying capacity of reinforced concrete (RC) slabs may be compromised for a number of reasons, including structural damage, design errors, building code changes and alteration of functional use.
Many concrete structures such as marine structures, bridge decks and parking garages reinforced with conventional steel reinforcements are susceptible to corrosion due to aggressive environmental conditions. The non-corrosive fibrereinforced polymers (FRPs) have been used gradually over the past two decades as internal and external reinforcements in concrete structures to avoid these problems. The use of FRP reinforcements in concrete structures affords a potential for increasing life and environmental benefits . The behaviour of FRP reinforced concrete members is typically quite different from that of conventional reinforced concrete members. FRP reinforcements have lower weight, high tensile and transverse shear strength than conventional steel reinforcements. Recently, basalt fibrereinforcedpolymer (BFRP) has been increased in civil engineering applications due to their advantageous characteristics compared with other FRPs, such as carbon FRP, Glass FRP and Aramid FRP.
Fibrereinforcedpolymer (FRP) composites have been widely used in construction due to their high tensile strength and durability performance, light weight, and ease of installation. FRP as a sheet or laminate can be used in shear or flexural strengthening of the beams, joints or slabs, in which the FRP contributes to transfer the load between two surfaces (Hadigheh et al., 2015). The use of FRP as the connecting element could be a potential option to achieve higher composite action in TCC systems. This paper focuses on the development of alternative TCC connections with improved structural performance. Various connections are designed and tested using cross laminated timber (CLT) panels. A combination of more traditional notch system and advanced fibrereinforcedpolymer sheets are used to achieve composite action. During the tests, photogrammetry is used for monitoring of the joint.
such as a widening of the slab support with concrete mushrooms or steel heads (Martinez- Cruzado et al. 1994; Hassanzadeh 1996). In addition, the bending resistance of the slab can be increased with an external reinforcement made of steel or new materials like fiber-reinforcedpolymer (FRP) composites (Harajli and Soudki 2003; Ebead and Marzouk 2004; Chen and Li 2005; Esfahani et al. 2009; El-Enein et al. 2014). For both concepts the behavior of the slab remains brittle however. A third possibility is the installation of additional shear reinforcement, which normally increases ductility; examples are shear studs (Menétrey and Brühwiler 1997; El-Salakawy et al. 2003; Adetifa and Polak 2005; Fernández Ruiz et al. 2010; El-Shafiey and Atta 2011; Feix et al. 2012; Polak and Bu 2013), drop panels (Martinez-Cruzado et al. 1994; Ebead and Marzouk 2002), FRP shear bolts (Lawler and Polak 2011; Meisami et al. 2013) or stirrup solutions with FRP laminates (Binici and Bayrak 2005a; Sissakis and Sheikh 2007). In some cases, the elements are prestressed for immediate unloading of the slab (Menétrey and Brühwiler 1997; El-Shafiey and Atta 2011). However, in the case of prestressed bolts, due to their short length, even small deformations caused by creep for example can substantially decrease the designated prestressing force. Faria et al. (2009, 2011) strengthened square concrete slabs with a side length of 2.3 m and 100- or 120-mm thickness with prestressed steel strands. These were placed above the column on the upper concrete surface and anchored on both sides in the bottom part of the slab, in holes drilled at an inclination of ca. 11°, using an epoxy adhesive. The punching resistance was increased by 34–48% for slabs with two strands in one direction only and by 61% for one slab with strands in both directions. The prestressing method also improved the serviceability limit state and the post-collapse behavior where a second peak load at 78% of the first peak load
The tensile strength of GFRP is 3000-4800 mpa where as CFRP is 2400-5100 mpa. In the various RC structure such as column, slab, beam can be strengthened using FRP.A vast amount of literature on the structure including flexure and torsion is available  . Still the R.C deep beam with CFRP strips is open for research. In reinforced structure (RC) structure the corrosion of steel reinforcement is a major cause of deterioration  . Since the use of FRP (FibreReinforcedPolymer) material is improving to solve the major problem for increase the service life of structure.
Precast prestressed hollow core (PHC) slabs are widely used as floor deck systems. However, as extrusion is the most widely adopted manufacturing technique of PHC slabs, it is difficult to arrange shear reinforcement during casting using an extrusion machine. Therefore, the shear capacity of a PHC slab relies on the shear strength of plain concrete, which makes them prone to shear failure near the support. Traditional solutions to increase the shear capacity of PHC slabs would add more weight and cost. Externally bonded fibrereinforced polymers (FRP) sheets have been successfully used over the past 20 years as an efficient technique for strengthening both the flexural and shear capacities of reinforced concrete members. During the first two phases of this research project, externally bonded carbonfibrereinforced polymers (CFRP) sheets along the internal perimeter of the PHC slab voids have proven to considerably increase the shear capacity of PHC slabs by up to 40%. The objective of the current research, which is Phase III, is to investigate and compare the effectiveness of glass fibres reinforced polymers (GFRP) sheets to CFRP sheets used in Phase I and Phase II to enhance the shear capacity of PHC slabs. A total of 11 full size PHC slabs, 1219 mm wide, 4500 mm long and 305 mm thick, were tested in Phase III. The effects of fibre type, the prestressing level, the width of the GFRP sheets, and the installation procedures for the shear capacity of PHC slabs were investigated. The ultimate strength, deflection, strands’ slippage, concrete strain and FRP strain were recorded, analyzed and compared to the results obtained in the previous study. The testing results show significant enhancement in the shear capacity and the behaviour of the PHC slabsstrengthened by externally bonded GFRP sheets along the internal perimeter of the PHC slab voids comparable to the effect of the CFRP sheets.
2000; Rankin and Long, 1997; Wood, 1961) for RC, SFRC and strengthenedfibre-reinforcedpolymer (FRP) members (Zeng et al., 2016), sector models based on axisymmetric assumptions (Einpaul et al., 2015, 2016) and finite-element methods (Belletti et al., 2016; Soares and Vollum, 2015). Membrane action effects on continuous slabs have been recently analysed using nonlinear finite-element analysis (NLFEA) and different modelling approaches, for example using three- dimensional (3D) hexahedral elements (Genikomsou and Polak, 2017) or multi-layered shell elements (Cantone et al., 2016). In this paper, the shrinkage effects on concrete cracking and on the punchingshear resistance are studied. This aspect could be significant for the structural assessment of existing structures carried out using refined numerical tools, such as NLFEA methods, which are able to take into account hidden resistance capacities, but are less conservative than analytical approaches (Belletti et al., 2015a, 2015b).
perimeter dimensions of the punchingshear failures (Dulude et al. 2013; Hassan et al. 2013a; Hassan et al. 2013b). Moreover, effects of different reinforcement diameters with constant reinforcement ratio which was included in this project weren’t addressed previously in the past research work. More test specimens are needed to cover a wider range of data, especially in this part of the mentioned parametric study to enable a more precise prediction of the punchingshear stress. On the other hand, the accuracy of current equations in the FRP design codes and guidelines CSA S806 (2012), ACI 440(2015), and JSCE (JSCE et al. 1997) and other design approaches from the literature are assessed. This research also develops a new database of results from concentric punchingshear tests of GFRP reinforced concrete flat slabs. Hence, this work aims to provide useful information to researchers and practising engineers. While FRP bar properties have been commercially improved, a review study of punchingshear behaviour is required.
Conversly, LWA are not strong as conventional aggregates. When the cracks star to develop; theses cracks will pass through th aggregate particles without any resistance. The failure is developed by the tensile stresses initiated within the aggregate particles as well as by the failure developed in the concrete paste surrounding the aggregate particles. The crack width and intensity are higher in LWC compared with NWC. Briefly, LWC is weak compared with NWC. Furthermore, the cracking strength or the tensile strength of LWC is significantly lower than the NWC of the same grade of concrete. This issue also influnce the shear capacity of LWC, bond between steel and concrete as well as the anchorage strength, etc. (Clarke, 2002). LWC has been used increasingly over the past decades (Aljaafreh, 2016). Table (1.1) summarises the most important LWC buildings constructed in the last 70 years. In the coming decades, it is therefore expected that structures constructed using LWC will occupy a significant proportion of the concrete infrastructures. When deteriorated, these structures may be retrofitted using efficient systems such as FRP reinforcement.
A series of the elements tested by Swamy and Ali  were selected to gain a better understanding of the predicted effect of the steel ﬁbre volume on the punchingshear strength of slab– column connections. The selected test elements had identical geometrical dimensions and ﬁbre type and the concrete compres- sive strength was similar for all batches. The failure criteria and the estimated load rotation relationships for the elements selected are presented in Fig. 9 a. As is shown in Fig. 9 b, the proposed model predicts well the increase of the punchingshear strength with the increase of the ﬁbre volume. Furthermore, an increase in the quantity of similar ﬁbres provides for an increase in the deforma- tional capacity. As the concrete contribution to the punching strength decreases with the increase of the slab rotation, the weight of the ﬁbre contribution becomes more relevant to the resistance mechanism. The predicted concrete and ﬁbres contribu- tions to the punchingshear strength for elements tested by Swamy and Ali (  are shown in Fig. 9 b, with an excellent correlation ob- served between the model predictions and the test results. 5. Code-like formulation
1800 mm divided into three equal length regions, two shear span regions and a constant moment region containing the lap splice. The splice length was 300 mm to maintain the minimum length allowed by the ACI and the Canadian standards, and to ensure a bond failure before the steel yielding. Each beam was reinforced with two 20M steel rebars spliced at the mid span. The lab splice was placed in the constant moment region to study the effect of the FRP wrapping on the bond strength where the nominal stress is uniform and there is no shear stress. Two 10M deformed bars were used in the compression zone outside the constant moment region. This test beam was designed without internal transverse reinforcing stirrups within the constant moment region of the splice to allow a separation of the effect of confinement by the U-shaped FRP sheets on the bond strength from the effect of confinement by stirrups. The internal transverse reinforcement in the shear spans consisted of 10M stirrups distributed at 100 mm spacing. The ratio of the lap splice length to the steel bar diameter l s /d b was 15.
According to Reuvers et al. , the development of an EIS spectra with time for a coating system can be divided into three stages: (1) a polymer ﬁlm is exposed to the solution and water starts to enter the polymer, (2) the entered water reaches the metal matrix, and (3) the polymer containing a signiﬁcant amount of water becomes conductive and the water ﬁlls the interface of polymer/metal. The surface polymer layer of a CFRP can be regarded as a coating on carbon ﬁbre bundles in the study (epoxy as coating and carbon ﬁbre as conductive matrix). Corresponding to the three stages, the CFRP surface layer will have a decreasing capacitive resistant behaviour (i.e., the resistance plateau and the following capacitance slope) ﬁrstly and then another capacitive resistant behaviour will appear (Fig. 5). The EIS results supported the different changes of the galvanic processes of the E-CFRP/metal and T- CFRP/metal couples with immersion time (Fig. 8). The E-CFRP had a much higher impedance in the low frequency range than the T-CFRP initially. However, it decreased with immer- sion time, while the low frequency impedance of the T-CFRP decreased and reached a relatively stable value quickly. The electrochemical process on the T-CFRP was always controlled by diffusion process (see the Warburg impedance characteris- tics in Fig. 5). These conﬁrm that the electrode state changed with immersion time. In addition, T-CFRP exhibited a dif- fusion control process at low frequencies while E-CFRP did not (Fig. 5). It should be noted that both the CFRPs had a diffusion control process at low frequency, but the diffusion behaviour of E-CFRP could be concealed by its large resistance and thus could not be exhibited in the frequency range in the study. The diffusion-controlled processes of both the CFRPs disappeared when their surface polymer layers were removed (Fig. 6), meaning that the surface polymer layers did signiﬁ- cantly affect the galvanic processes.
An experimental program was carried out by Rizk et al. (2011) to investigate the influence of the slab size on the punchingshear resistance. Five thick square slabs were tested. The slabs were 300 mm and 400 mm thick with side dimension of 2650 mm. The slabs were loaded through a small column stub 400 × 400 mm. Four slabs were cast using high strength concrete and one using normal concrete. Shear reinforcement was used in one of the high strength concrete slab. The results of the punchingshear strength showed good agreement with the values predicted using the CEB-FIP Model Code (1990). The ACI 318-11 code was found to underestimate the punchingshear strength for all slabs by an average of 17% except for one high strength concrete slab. This high strength slab had the lowest reinforcement ratio and the predicted value was overestimated by 19%. It was highlighted by the authors that the experimental shear strength was different in two slabs. The slabs had different concrete strength, similar slab thickness and reinforcement ratio. Both slabs were designed to fail under punchingshear stresses. This finding showed that having a constant number for the size effect factor depending on the slab depth only, as used in major design codes, may not account for the size effect and it should also include the concrete compressive strength.