Design method for RC beam retrofitting using global energy balance

Abstract

Flexural retrofitting of RC beams using FRP plate is a common way to increase the flexural capacity. Retrofitted beams commonly fail by debonding of the FRP plate, which occurs well before the target flexural capacity. Debonding prevention has been accounted-for empirically in most design approaches so far. The Global Energy Balance Approach (GEBA) using fracture mechanics has been proposed to determine the debonding load of an FRP-RC beam that is affected by the plate curtailment location. The GEBA results for various FRP-RC beams can be summarised using debonding contours on plots of moment capacity against the safe plate curtailment locations, and the debonding contours constructed in this way for the beams with the same ratio of depth to fracture energy are virtually the same. This paper shows how GEBA can be incorporated into the design process to prevent premature debonding of the FRP plate. The method makes use of the debonding contours and derives from these simplified design charts that could be made available to designers. The retrofitting design consideration and the theoretical background of this unified design method are first explained, followed by the derivation of the conceptual design charts. Numerically correct design charts are then constructed for a wide range of design cases. Finally, a worked example is used to explain the way to apply the unified design method using design charts.