【正文】 ed of four specimens. The details and dimensions of the specimens designated series SW are illustrated in Fig. 1a. In this series, four 32mm steel bars were used as longitudinal reinforcement with two at top and two at bottom face of the crosssection to induce a shear failure. The specimens were reinforced with 10mm steel stirrups throughout their entire span. The stirrups spacing in the shear span of interest, right half, was selected to allow failure in that span. Series SO consisted of eight beam specimens, which had the same crosssection dimension and longitudinal steel reinforcement as for series SW. No stirrups were provided in the test half span as illustrated in Fig. 1b. Each main series (. series SW and SO) was subdivided into two subgroups according to shear spantoeffective depth ratio. This was selected to be a/d = 3 and 4, resulting in the following four subgroups: SW3。/0176。ply] was selected to investigate the impact of additional horizontal restraint on shear strength. In series SW4, specimen SW42 was strengthened with two CFRP plies having perpendicular fiber direction (90176。). Specimen SO35 was strengthened with two CFRP plies (90176。/0176。/0176。, and the 12 wrapping scheme is expressed in Eqs. (6a) and (6b)。cf :Nominal concrete pressive strength (MPa) fef :Effective tensile stress in the FRP sheet in the direction of the principal fibers (stress level in the FRP at failure) fuf :Ultimate tensile strength of the FRP sheet in the direction of the principal fibers eL :Effective bond length (mm) R: Reduction coefficient (ratio of effective average stress or strain in the FRP sheet to its ultimate strength or elongation) fs :Spacing of FRP strips ft :Thickness of the FRP sheet on one side of the beam (mm) cV :Nominal shear strength provided by concrete fV :Nominal shear strength provided by FRP shea。GPa is being conducted at the University of Missouri, Rolla (UMR). . Upper limit of the reduction coefficient In order to control the shear crack width and loss of aggregate interlock, an upper limit of reduction coefficient, R, was suggested and calibrated with all of the available test results [10] to be equal to fu?/ where fu? is the ultimate tensile CFRP strain. This limit is such that the average effective strain in CFRP materials at ultimate can not be greater than mm/mm (without the strengthening reduction factor,? ). . Controlling reduction coefficient The final controlling reduction coefficient for the CFRP system is taken as the lowest value determined from the two possible modes of failure and the upper limit. Note that if the sheet is wrapped entirely around the beam or an effective end anchor is used, the failure mode of CFRP debonding is not to be considered. The reduction coefficient is only controlled by FRP fracture and the upper limit. . CFRP spacing requirements Similar to steel shear reinforcement, and consistent with ACI provision for the stirrups spacing [12], the spacing of FRP strips should not be so wide as to allow the formation of a diagonal crack without intercepting a strip. For this reason, if strips are used, they should not be spaced by more than the maximum given in Eq. (8). . Limit on total shear reinforcement ACI 318M95 [12] and set a limit on the total shear strength that may be provided by more than one type of shear reinforcement to preclude the web 13 crushing. FRP shear reinforcement should be included in this limit. A modification to ACI 318M95 Section was suggested as follows: . Shear capacity of a CFRP strengthened section — Eurocode format The proposed design equation wEq. (3)x for puting the contribution of externally bonded CFRP reinforcement may be rewritten in Eurocode (EC2 1992) [15] format as Eq. (10). In this equation, the partial safety factor for CFRP materials, f? , was suggested equal to [10]. . Comparison between the test results and calculated values The test summary and the parison between the test results and the calculated shear strength, using the design approach (ACI format), are detailed in Tables 2 and 3, respectively. For CFRP strengthened beams, the measured contribution of concrete, Vc , and steel stirrups, Vs, (when present) were considered equal to the shearstrength of a nonstrengthened beam. The nominal shear strength provided by concrete and steel stirrups was puted using Equations (115) and (1115) in ACI 31895 [12]. In Equation (115), the values of Vu and M u were taken at the point of application of the load. The parison indicates that the design approach gives conservative results for the strengthened beams as illustrated in Fig. 13. 5. Conclusions and further remendation An experimental investigation was conducted to study the shear behavior and the modes of failure of simply supported rectangular section RC beams with shear deficiencies, strengthened with CFRP sheets. The parameters investigated in this program were existence of steel shear reinforcement, shear spantoeffective depth ratio (ayd ratio), and CFRP amount and distribution. The results confirm that the strengthening technique using CFRP sheets can be used to 14 increase significantly shear capacity, with efficiency that varies depending on the tested variables. For the beams tested in this program, increases in shear strength of 40–138% were achieved. Conclusions that emerged from this study may be summarized as follows: ● The contribution of externally CFRP reinforcement to the shear capacity is influenced by the a/d ratio. ● Increasing the amount of CFRP may not result in a proportional increase in the shear strength. The CFRP amount used to strengthen specimen SO34 was 250% of that used in specimen SO32, which resulted in a minimal (10%) increase in shear capacity. An end anchor is remended if FRP debonding is to be avoided. Table2