【正文】 ent for bond, the effective bond length, eL , has to be determined first. Based on analytical and experimental data from bond tests, Miller [14] showed that the effective bond length slightly increases as CFRP axial rigidity, ffEt , increases. However, he suggested a constant conservative value eL for equal to 75 mm. The value may be modified when more bond tests data bees available. After a shear crack develops, only that portion of the width of CFRP extending past the crack by the effective bonded length is assumed to be capable of carrying shear.[13] The effective width, feW , based on the shear crack angle of 45176。) resulted in a concrete splitting failure rather than a CFRP debonding failure. The failure occurred at total applied load of 339 kN with a 120% increase in the shear capacity pared to the control specimen SO31. The strengthening with two perpendicular plies (. 90176。) 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。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。） .This ply [. 0176。 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。 Shear。 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 of Alexandria, Alexandria 21544, Egypt bDepartment of Civil Engineering, University of Missouri at Rolla, Rolla, MO 65409, USA Received 28 April 1999。 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 consist