International Journal of Architectural, Civil and Construction Sciences ISSN: 2415-1734 Vol:12, No:10, 2018 1028 1 Abstract—The reduction in dapped end beams depth nearby the supports tends to produce stress concentration and hence results in shear cracks, if it does not have an adequate reinforcement detailing. This study investigates numerically the efficiency of applying different external strengthening techniques to the dapped end of such beams. A two-dimensional finite element model was built to predict the structural behavior of dapped ends strengthened with different techniques. The techniques included external bonding of the steel angle at the re-entrant corner, un-bounded bolt anchoring, external steel plate jacketing, exterior carbon fiber wrapping and/or stripping and external inclined steel plates. The FE analysis results are then presented in terms of the ultimate load capacities, load-deflection and crack pattern at failure. The results showed that the FE model, at various stages, was found to be comparable to the available test data. Moreover, it enabled the capture of the failure progress, with acceptable accuracy, which is very difficult in a laboratory test. Keywords—Dapped-end beams, finite element, shear failure, strengthening techniques, reinforced concrete, numerical investigation. I. INTRODUCTION RECAST concrete girders with dapped ends are commonly used in parking structures, pedestrian bridges, and in long-span bridges. Although, dapped ends are useful in reducing the structure’s height, two dramatic problems are resulted. The first problem is that the shear stresses at the end of the beam must be carried by a much smaller section. The second one is the stress concentration near re-entrant corner of dapped end that usually produces wide cracks at this area. These cracks increase the danger of damage due to corrosion. Unfortunately, the mechanism of load transfer through dapped ends is hard to represent using conventional design procedures. Because of these challenges, the design of dapped ends requires special produces [1], [2]. PCI design handbook [3] describes the five potential failure modes for dapped end. These failure modes are caused by flexure and axial tension at the extended end, and direct shear and diagonal tension in the un-dapped portion. The external strengthening techniques have shown great influence in repairing and strengthening of dapped end beams capacity. Holden et al. [4] experimentally tested precast system that combined post-tensioned unbounded carbon fiber A. Abdel-Moniem (Master Student) is with the Aswan University, Egypt (e-mail: abdelnasermi@gmail.com). H. Madkour and K. Farah are with the Structural Engineering Department, Aswan University, Egypt Abdullah is with the Structural Engineering Department, Aswan University, Egypt and Civil Engineering Department, Bisha University, Saudi Arabia. tendons and steel fiber reinforced concrete. Hanson [5] declared the results of testing and estimation of pocketed spandrel beams that included dapped-ends. Huang [6], [7] tested precast pre-stressed concrete double tee members strengthened using FRP composites. They tested two different strengthening techniques (0 o /90 o ) wrapping and compared them to get a better understanding of the dapped-end behavior and the efficiency of using externally bonded fiber reinforced polymers (FRP) composites. Valerio [8] used vertical steel and fiber-reinforced plastic bars to be inserted into pre-drilled holes and vaulted in place using epoxy resin for shear strengthening of existing concrete bridges. FRP applied using the externally bonded reinforcement (EBR), or near surface mounted reinforcement (NSMR) techniques have been proven to be efficient for strengthening RC structures [9]-[11]. Gold et al. [12] strengthened with FRP several dapped-end beams of a three- story parking garage that were insufficient in shear capacity. A series of tests were carried out to verify the effectiveness of the FRP strengthening as well as the predictive performance of their design approach. Taher [13] studied the efficiency of some strengthening techniques for increasing the capacity of dapped-end beams. Tests for 52 rectangular beams showed that the using of FRPs produces the best way for strengthening and retrofitting of dapped end. Using Strut and Tie Method (STM), Taher also estimated the capacity of the FRP-strengthened dapped-end beams. Nevertheless, this model did not take into consideration any size effects of dapped ends. Tan [14] studied the effectiveness of many FRP arrangements for strengthening dapped-end beams with insufficient shear resistance, consisted of both fiber types and mechanical anchorage systems for FRPs. The results illustrated that the ultimate load increased by 43, 75, 80 percent for carbon fiber plates (CP), carbon fiber sheets (CS), and glass fiber fabrics (GS) systems, respectively. He has also shown that the tested mechanical anchorage devices provided higher profiteering of the FRP systems’ strengthening capacity by prohibition their deboning. Huang and Nanni [15] tested the FRPs capability to improve the capacity of dapped-end beams, and Atta et al. [16] produced an experimental investigation for the torsional behavior of recessed RC beams and studied the application of FRP sheets, FRP laminates and external pre-stressing steel under torsional moments. Gyorgy et al. [17] studied experimentally and numerically the efficiency of strengthening dapped-end reinforced concrete beams using externally bonded carbon FRP. Numerical Investigation for External Strengthening of Dapped-End Beams A. Abdel-Moniem, H. Madkour, K. Farah, A. Abdullah P