Efficiency of repair of HSC beams subjected to combined forces by GFRP sheets

摘要

The introduction of fiber reinforced composite materials in civil engineering has progressed at a very rapid rate in the recent years. The high-performance materials, which consist of high strength fibers, embedded in the plastic matrix, possess unique properties, which make them extremely attractive for a wide range of structural applications. An area where the use of fiber reinforced composites has attracted considerable interest is the repair and retrofitting of R.C. structural elements, but what about elements cast using high strength concrete. The global aim for this study was finding the structural efficiency restored after increasing lateral confinement of the high strength concrete box - section beams. In this study, glass fiber plastic sheets were used in retrofitting of structurally deficient R.C. beams due to combined shear and torsion, e.g. spandrel beams - curved beams -spiral staircases. Such beams failed in a brittle manner. The experimental program contained seven damaged beams wrapped by two layers of unidirectional GFRP sheets. Parameters investigated were reinforcement percentage (whether under or over reinforcement according to the (ACI 318-95) and the accompanied applied shearing force level. Beams dimension were 25 X 40cm with a box-section wall thickness of 6.5cm and tested zone of 100cm. The efficiency of repairing such beams by this wrapping system using GFRP sheets was investigated and the percentages of restored characteristics were calculated after being tested. Behavioral characteristics were recorded under monotonically increasing torque until failure. Load - strain relationships were illustrated and conclusions are presented. Comparison between beams cast using normal and high strength concrete are presented also, the experimental work was held in the reinforced concrete lab through a scheme for "Application of Modern Composites in Repair and strengthening of Structural Elements" sponsored by the Housing and Building Research Center (HBRC).