Comparative Study of Unbonded Carbon Fiber and Steel Strands in Posttensioned Pier Caps

Carbon fiber strands offer a viable alternative to corrosion-prone steel strands in posttensioning applications. This study focused on a side-by-side comparison of two types of carbon fiber strands with different elastic moduli against steel strands in a 51/2:1 scaled model of a typical interior hammerhead pier of the San Antonio DowntownY project with two identical cantilever overhangs. Two different strand arrangements were used for posttensioning, with eight and six strands, respectively representing an overdesign and a slight underdesign relative to the factored demand. The model was tested under service and factored flexure and shear loads. The study confirmed the feasibility of using carbon fiber strands in unbonded posttensioning of pier caps. Given the strength-based design of the pier cap, the elastic moduli of different carbon fiber strands did not seem to have affected the serviceability performance with respect to either cracking or deflection. Considering both serviceability and overload conditions, the general performance of the pier cap model under both flexure and shear loading was deemed acceptable using either type of carbon fiber strands, and quite comparable to that of steel strands. (C) 2015 American Society of Civil Engineers.