Strength design equations for FRP-strengthened concrete beams

Externally-bonded fibre-reinforced polymer (FRP) has been established as the technology of choice to strengthen reinforced concrete beams. Researchers and practicing engineers have recently developed design guidelines for FRP strengthening. However, the current state of the art flexural design procedure suggests an iterative process. No earlier efforts have been devoted to develop direct strength design equations on the failure modes of FRP rupture and delamination that can facilitate structural calculations. This study develops exact and approximate sets of closed form equations to design singly-and doubly-reinforced strengthened rectangular sections that fail by FRP rupture or cover delamination. Comparisons with reported experimental strength data indicate excellent agreement. A comprehensive parametric study, including flat and wrapped FRP sheets and laminates, has yielded a simple linear equation that has an almost perfect statistical correlation, and is equally applicable to analysis and design. The equation is found to be unique regardless of the height of the wrapped side of FRP flexural sheets.