Determination of optimum bond thickness of reinforced concrete beam strengthened externally by bonded steel plates

Abstract

Epoxy bonded steel plate (EBP) had been shown to be an effective structural strengthening method for degraded and old civil structures.  A good number of research have been geared to study strengthening technique over the last two decades. However, the optimum bond  thickness that would be structurally acceptable remains a gap in the literature. The intention of this study is to determine experimentally  the optimum bond thickness of reinforced concrete (RC) beam strengthened externally by bonded steel plates. To achieve the aim, thirty- Nine (39) beams were tested. Each beam sample had 100 x 150 mm cross section and 1100mm length with a shear span to depth ratio  (av/d) of 2.5 and were reinforced with 2ϕ10 mm and 2Φ8 mm reinforcements in the zone presumed to go into tension and compression  respectively. The shear reinforcements were provided with Φ6mm links at 220mm centre to centre. Four bond layer thicknesses, 2 mm,  4mm 6 and 8mm, were chosen. For each bond layer thickness, three (3) levels of plate thickness were chosen-l.0 mm, 1.5 mm, and 2mm,  all with constant breadth and length of 80mm and 1000mm respectively. The tension surfaces of the beams were prepared to remove all  cement paste and were thoroughly cleaned of loose particles. Both side of the steel plates were totally cleaned and then kept  safeguarded from contamination. The two-part structural epoxy resin was mixed thoroughly and bonded to the tension surfaces of the  beams to the required thickness-2mm, 4mm, 6mm, and 8mm. the steel plate was placed at the right location, and kept in position for  proper boding. At least 7-day was allowed between strengthening and loading of the beams. The beams were strengthened with 1, 1.5  and 2mm thick plates of four different levels of bond thickness-2mm, 4mm, 6mm, and 8mm respectively at the tension face. All the  beams were instrumented as simply supported. According to the findings, there is a maximum bond thickness that would be structurally  acceptable for RC beams strengthened or upgraded with structural steel plate. Results also confirmed that as the bond thickness  increases, the ductility index reduces. Strengthening reinforced concrete beam with steel plate increases the stiffness of the beam. In  order to maintain composite behavior up to the point of failure, steel plate thickness to bond thickness ratio should be kept within the  range of 0.3 to 0.4 for beams strengthened while the thickness-to-width ratio of steel plates shall not be more than 0.015