Recent progress on seismic strengthening of concrete diaphragms with FRP ties

Abstract

Concrete floor diaphragms in existing buildings are often inadequate to resist tension forces developed as the diaphragm spans between the lateral load resisting elements. A common strengthening method to provide additional tension capacity is through Fibre Reinforced Polymer (FRP) ties. However existing research has been limited to thin and short FRP ties which are dissimilar to those typically required for diaphragm strengthening applications. This paper summarises the progress to date on an extensive research programme to develop a method for seismic strengthening of diaphragms with FRP, including experimental carried out to date. More specifically, the completed research has yielded three main outcomes, a) better understand of the behaviour of thick and long FRP ties, with and without anchors, b), the tension-rotation response of precast units with respect to support beams, and c) flexural and shear strengthening of diaphragms. A brief summary of the upcoming work is included, mainly focusing on more precast testing considering both rotational, collector behaviour and global behaviour at a diaphragm and building level.