Bond studies of FRP confined hooked bar anchorages in high strength concrete structures

ABSTRACT

The objective of the research reported in this paper was to evaluate the effect of fiber reinforced polymer (FRP) sheets, externally confining high strength concrete beamcolumn joints, on the bond strength and ductility of the mode of failure of hooked bars anchored in the joints. Twelve beam-column specimens with a nominal concrete strength of 60 MPa, were tested. The specimen simulated the rigid connection of a cantilever beam to a column. It consisted of a vertical beam element anchored in a column base. The tensile reinforcement of the beam consisted of two bars anchored in the base using hooked bar anchorages. The variables were the beam bar size (16, 25, or 32 mm), the confinement mode of the beam bars in the beamcolumn joint (whether the bars were confined within or outside the column reinforcement cage), and whether or not the joints were externally wrapped with FRP sheets. Specimens where the beam bars were anchored within the column reinforcement cage were referred to as “confined specimens”, and specimens where the beam bars were anchored outside the column reinforcement cage were referred to as “unconfined specimens”. All anchorages were designed to ensure bond splitting failure before the beam bars yielded. The effect of FRP was assessed by comparing the performance of specimens with no FRP with companion specimens that had FRP sheets externally wrapping the beam-column anchorage zones but identical otherwise. Comparison was based on the mode of failure, load-deflection behavior, and the bond strength. FRP sheets were found effective in increasing the anchorage capacity and the ductility of the loaddeflection behaviour. The improvement was more significant for the “unconfined specimens”than the “confined specimens”. The conclusions are valid for all bar sizes tested.