Use of unstressed strands for connections of precast concrete members

Precast concrete members need to be connected effectively to form an integral structural system. Use of unstressed strands provides a cost-effective and practical solution to reinforce the connection regions of precast concrete members, especially for precast concrete bridge girder applications. With the limited understanding of bonding characteristics for unstressed strands, a combination of experimental and analytical programs, which focused on unstressed strands as a connection between precast concrete girders and cap beams for seismic applications, was designed to investigate the fundamental load-transfer characteristics of unstressed strands anchored in grout and concrete based on pullout tests. The relationship between strand stress and loaded-end displacement was developed, and the bond stress of unstressed strands embedded in concrete and grouted duct was examined. The average bond stress of unstressed strands anchored in concrete and grouted duct is recommended to be five and seven times the square root of concrete compressive strength, respectively. The results of this research provide qualitative embedment length requirements to design connections between precast concrete members using unstressed strands.