Author(s): Tarek Ali, Sameh Yehia
This paper presents a focused study on using different methods to enhance the ultimate capacity of flexural behavior in RC slabs. Four RC specimens were casted with common compressive strength and reinforced with steel mesh. Specimens were strengthened with different methods such as usage of GFRP sheets, carbon fibers laminate strips and near surface mounted steel rebars. All specimens were subjected to two-point loading setup. Load was increased from zero to failure load. First crack was recorded and crack pattern was observed. The behavior of strengthened specimens was compared to that of the control specimen to judge the efficiency of the used techniques. Test results showed that the used techniques were effective in enhancing the behavior of the strengthened slabs by noteworthy values.
There is no doubt that the problem of cracked concrete structures has become one of the most pressing problems that must join hands in efforts to reach a solution before cracks appear in structure. Some of concrete structures that were built in the past years were inadequate to carry service loads. This insufficient load carrying capacity has resulted from poor maintenance, increasing in legal load limit, insufficient reinforcement, excessive deflections, structural damages or steel corrosion, which leads to cracks. Repair, retrofitting and rehabilitation of existing concrete structures have become a large part of the construction activity; also the money spent on retrofitting of existing structures in recent years has exceeded that spent on new structures due to using traditional techniques . The restoration, strengthening and retrofitting of concrete are work of rehabilitation/treatment adjustments to the structural elements (such as foundations, columns, beams and slabs) so that beams are recorded soundness values in strengthening and retrofitting by using FRP in the worst case of loading such as cyclic loads .
Enhancing the cracking loads and mode of failure of slabs as flexural elements is demanding  . Therefore, in this research, the problem was handled and studied by testing four RC slab specimens strengthened using three different techniques to judge their effectiveness in enhancing the behavior of the strengthened slabs in addition to one pilot specimen. Nowadays, generally new techniques appear in strengthening field. One of the important structural elements is slab which is may crack due to overloading, change of building function, or fabrication errors.In this research, efficiency of slab strengthening was judged by comparing the behavior of strengthened specimens from the point of view of cracking and ultimate loads, cracking mechanism, and mode of failure. This research was focused on studying three of the most popular innovative slab strengthening techniques: GFRP sheets, carbon fiber laminate strips, and near surface mounted steel rebars.
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