THE STRUCTURAL BEHAVIOUR AND ULTIMATE STRENGTH OF REINFORCED CONCRETE SLABS SRENGTHENED BY EPOXY-BONDED STEEL PLATES

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Department of Engineering

ABSTRACT
The structural behaviour and ultimate strength of concrete slabs strengthened by epoxy-bonded steel plates was studied by both analytical and experimental investigations. The purpose was to evaluate their structural response at the serviceability and ultimate limit states. Simple analytical models that predict the ultimate behaviour of reinforced concrete slabs with epoxy-bonded steel plates on the tension face in the elastic and plastic regions were developed. The analytical models were evaluated by comparing analytical results with the test data for 13 slabs. Thirteen concrete slabs were tested to failure under central point load. The measured load versus deflection at midspan of the slabs and the load versus strain in steel plate were plotted and compared with the control slabs. The ratio of the ultimate load of plated slabs to unplated slabs was 4.78 and 1.92, for tension reinforcement ratio 0.00 and 0.71 respectively. The presence of glue alone enabled the slabs to carry higher ultimate loads by up to 45 percent. These results clearly indicated the beneficial effect of bonded plates in enhancing the ultimate flexural strength of reinforced concrete slabs. The glued plates also reduce the deflection and steel plate strain at different rates and that the rate of reduction varies with the applied load level. However, the stiffening effect of the glued plates is much greater in controlling cracking than in controlling deflection. Comparisons of the analytical results with the test data obtained for thirteen concrete slabs were also carried out. The average ratio of experimental to theoretical ultimate moment of both plated and unplated slabs was of the order of 1.00, with a minimum of 0.64 and a maximum of 1.15. Generally, a reasonably close agreement between the calculated and measured data was noted. The applicability of the plate bonding technique to strengthen structurally damaged reinforced concrete slabs was also examined. The structural behaviour of precracked slabs, loaded up to 45 percent of their flexural capacity, were reported. The results showed that strengthening, by epoxy-bonded steel plates, of cracked slabs is structurally efficient and that these plated slabs can carry higher ultimate load from 72 to 98 percent of the original unplated slabs. The restraining effect of the steel plates on the existing cracks was, however, more pronounced when the load was increased beyond the original preloading value. To explore the effectiveness of the epoxy give in preserving composite action, slippage at the interface was measured. The results revealed that provided epoxy with a wide range of strengths and ductilities are used and adequate precautions are observed in the gluing technique, both slab action and full composite behaviour can be maintained until failure. Slip measurements for the set of test slabs varied from 0.018 to 1.930 mm.