【正文】 kN. Specimen SO42, strengthened with CFRP strips, the failure was controlled by CFRP debonding at a total load of 255 kN with 96% increase in shear capacity over the control specimen SO41. The maximum local CFRP vertical strain measured at failure was mmymm. When paring the test results of specimen SO42 to that of specimen SO32, the 9 enhanced shear capacity of specimen SO42 (a/d=4) due to addition of CFRP strips was kN, while specimen SO32 (a/d=3) resulted in added shear capacity of 54 kN. As expected, the contribution of CFRP reinforcement to resist the shear appeared to decrease with decreasing a/d ratio. Specimen SO43, strengthened with continuous U wrap, failed as a result of concrete splitting at an applied load of 310 kN with a 138% increase in shear capacity pared to that of specimen SO41. The maximum local CFRP vertical strain measured at failure was mm/mm. 4. Design approach The design approach for puting the shear capacity of RC beams strengthened with externally bonded CFRP reinforcement, expressed in ACI design code [12] format, was proposed and published in 1998 [13]. The design model described two possible failure mechanisms of CFRP reinforcement namely: CFRP fracture。/0176。/0176。/0176。) similar to specimens SW32 and SW42. In series SO4, two beam specimens were strengthened. Specimen SO42 was strengthened with oneply CFRP strips in the form of Uwrap similar to specimen SO32. Specimen SO43 was strengthened with oneply continuous Uwrap (90176。). Specimen SO35 was strengthened with two CFRP plies (90176。) as for specimen SW32. Four beam specimens were strengthened in series SO3. Specimen SO32 was strengthened with oneply CFRP strips in the form of Uwrap with 90176。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。). The second ply was bonded on the two sides of the specimen with the fiber direction parallel to the beam axis（ 0176。/0176。 SO3。 Carbon fiber reinforced polymer 1. Introduction Fiber reinforced polymer (FRP) posite systems, posed of fibers embedded in a polymeric matrix, can be used for shear strengthening of reinforced concrete (RC) members [1–7]. Many existing RC beams are deficient and in need of strengthening. The shear failure of an RC beam is clearly different from its flexural failure. In shear, the beam fails suddenly without sufficient warning and diagonal shear cracks are considerably wider than the flexural cracks [8]. The objectives of this program were to: 2 1. Investigate performance and mode of failure of simply supported rectangular RC beams with shear deficiencies after strengthening with externally bonded CFRP sheets. 2. Address the factors that influence shear capacity of strengthened beams such as: steel stirrups, shear spantoeffective depth ratio (a/d ratio), and amount and distribution of CFRP. 3. Increase the experimental database on shear strengthening with externally bonded FRP reinforcement. 4. Validate the design approach previously proposed by the authors [9]. For these objectives, 12 fullscale, RC beams designed to fail in shear were strengthened with different CFRP schemes. These members were tested as simple beams using a fourpoint loading configuration with two different a/d ratios. 2. Experimental program . Test specimens and materials Twelve fullscale beam specimens with a total span of 3050 mm. and a rectangular crosssection of 150mmwide and 305mmdeep were tested. The specimens were grouped into two main series designated SW and SO depending on the presence of steel stirrups in the shear span of interest. Series SW consisted 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。 accepted 10 January 2020 Abstract The present study examines the shear performance and modes of failure of rectangular simply supported reinforced concrete(RC) beams designed with shear deficiencies. These members were strengthened with externally bonded carbon fiber reinforced polymer (CFRP) sheets and evaluated in the laboratory. The experimental program consisted of twelve fullscale RC beams tested to fail in shear. The variables investigated within this program included steel stirrups, and the shear spantoeffective depth ratio, as well as amount and distribution of CFRP. The experimental results indicated that the contribution of externally bonded CFRP to the shear capacity was significant. The shear capacity was also shown to be dependent upon the variables investigated. Test results were used to validate a shear design approach, which showed conservative and acceptable predictions.○C 2020 Elsevier Science Ltd. All rights reserved. Keywords: Rehabilitation。 1 英文原文： Rehabilitation of rectangular simply supported RC beams with shear deficiencies using CFRP posites Ahmed Khalifa a,* , Antonio Nanni b a Department of Structural Engineering, University