【正文】 of Alexandria, Alexandria 21544, Egypt bDepartment of Civil Engineering, University of Missouri at Rolla, Rolla, MO 65409, USA Received 28 April 1999。 received in revised form 30 October 2020。 Shear。SW4。 and SO4. 3 The mechanical properties of the materials used for manufacturing the test specimens are listed in Table of the specimens including surface preparation and CFRP installation is described elsewhere [10]. Table 1 . Strengthening schemes One specimen from each series (SW31, SW41, SO31 and SO41) was left without strengthening as a control specimen, whereas eight beam specimens were strengthened with externally bonded CFRP sheets following three different schemes as illustrated in Fig. 2. In series SW3, specimen SW32 was strengthened with two CFRP plies having perpendicular fiber directions (90176。). The first ply was attached in the form of continuous Uwrap with the fiber direction oriented perpendicular to the longitudinal axis of the specimen (90176。） .This ply [. 0176。/0176。fiber orientation. The strip width was 50 mm with centertocenter spacing of 125 mm. Specimen SO33 was strengthened in a manner similar to that of specimen SO32, but 4 with strip width equal to 75 mm. Specimen SO34 was strengthened with oneply continuous Uwrap (90176。/0176。) similar to SO34. . Test setup and instrumentation All specimens were tested as simple span beams subjected to a fourpoint load as illustrated in Fig. 3. A universal testing machine with 1800 KN capacity was used in order to apply a concentrated load on a steel distribution beam used to generate the two concentrated loads. The load was applied progressively in cycles, usually one cycle before cracking followed by three cycles with the last one up to ultimate. The applied load vs. deflection curves shown in this paper are the envelopes of these load cycles. Four linear variable differential transformers (LVDTs) were used for each test to monitor vertical displacements at various locations as shown in Fig. 3. Two LVDTs were located at midspan on each side of the specimen. The other two were located at the specimen supports to record support settlement. For each specimen of series SW, six strain gauges were attached to three stirrups to monitor the stirrup strain during loading as illustrated in Fig. 1a. Three strain gauges were attached directly to the FRP sheet on the sides of each strengthened beam to monitor strain variation in the FRP. The strain gauges were oriented in the vertical direction and located at the section midheight with distances of 175, 300 and 425 mm, respectively, from the support for series SW3 and SO3. For beam specimens of series SW4 and SO4, the strain gauges were located at distance of 375, 500 and 625 mm, respectively, from the support. 3. Results and discussion In the following discussion, reference is always made to weak shear span or span of interest. . Series SW3 5 Shear cracks in the control specimen SW31 were observed close to the middle of the shear span when the load reached approximately 90 kN. As the load increased, additional shear cracks formed throughout, widening and propagating up to final failure at a load of 253 kN (see Fig. 4a). In specimen SW32 strengthened with CFRP (90176。), no cracks were visible on the sides or bottom of the test specimen due to the FRP wrapping. However， a longitudinal splitting crack initiated on the top surface of the beam at a high load of approximately 320 kN. The crack initiated at the location of applied load and extended towards the support. The specimen failed by concrete splitting (see Fig. 4b) at total load of 354 kN. This was an increase of 40% in ultimate capacity pared to the control specimen SW31. The splitting failure was due to the relatively high longitudinal pressive stress developed at top of the specimen, which created a transverse tension, led to the splitting failure. In addition, the relatively large amount of longitudinal steel reinforcement bined with overstrengthening for shear by CFRP wrap probably caused this mode of failure. The load vs. midspan deflection curves for specimens SW31 and SW32 are illustrated in Fig. 5, to show the additional capacity gained by CFRP. The maximum CFRP vertical strain measured at failure in specimen SW32 was approximately mm/mm, which corresponded to 14% of the reported CFRP ultimate strain. This value is not an absolute because it greatly depends on the location of the strain gauges with respect to a crack. However, the recorded strain indicates that if the splitting did not occur, the shear capacity could have reached higher load. Comparison between measured local stirrup strains in specimens SW31 and SW32 are shown in Fig. 6. The stirrups 1, 2 and 3 were located at distance of 175, 300 and 425 mm from the support, respectively. The results showed that the stirrups 2 and 3 did not yield at ultimate for both specimens. The strains (and the forces) in the stirrups of specimen SW32 were, in general, smaller than those of specimen SW31 at the same level of loading due to the effect of CFRP. Fig. 6. Applied load vs. strain in the stirrups for specimens SW31 and SW32. . Series SW4 In specimen SW41, the first diagonal crack was formed in the member at a total 6 applied load of 75 kN. As the load increased, additional shear cracks appeared throughout the shear span. Failure of the beam occurred when the total applied load reached 200 kN. This was a decrease of 20% in shear capacity pared to the specimen SW31 with a/d ratio=3. In specimen SW42, the failure was controlled by concrete splitting similar to test specimen SW32. The total applied load at ultimate was 361 kN with an 80% increase in shear capacity pared to the control specimen SW41. In addition, the measured strains in the stirrups for s