Shear capacity evaluation of unbonded precast prestressed concrete beam-column joints caused volume loss by sheath tubes

Openings in joint panel were formed by sheath tubes in unbonded precast prestressed concrete (called as PCaP/C) structure. It was expected that beam-column joint shear strength was decreased by volume loss caused by openings within joint panel. The purpose of this study is to reveal the influence of volume loss caused by sheath tubes in joint panel for PCaP/C structure and to propose the simple method to calculate reduction coefficient (called as c_r). The specimens were previously tested in references. The volume loss rate (called as R_vl) caused by openings within joint panel was the percentage of a volume of sheath tubes in joint-panel divided by an effective joint-panel volume. As the R_vl increased, beam-column joint shear strength decreased gradually. When R_vl was smaller than 8.0%, the joint-panel area expanded both to the lateral and vertical direction after the peak. Particularly when the R_vl was greater than 8.0%, the joint-panel area expanded only to the lateral direction after the peak. This meant that joint panel was failed in a shear force not to horizontal direction but rather to vertical direction. Proposed reduction coefficient was multiplied by design strength of R/C beam-column joints calculated according to seismic design provisions by Architectural Institute of Japan (called as AIJ). Due to this coefficient, the reduction of joint shear strength could be taken into consideration.