Abstract
This thesis reviews and compares the design, construction, testing , and data analysis of three test specimens from the National Cooperative Highway Research Program (NCHRP) project 12-74: Cast-in-place (CIP) control specimen, the Cap Pocket Full Ductility (CPFD) specimen, and the Cap Pocket Limited Ductility (CPLD) specimen. The purpose of this thesis was to develop an innovative alternative to CIP construction using precast concrete and determine if its response is emulative. The cap pocket connections were achieved by forming a large void into the bent cap using a steel corrugated pipe, also intended to supply reinforcement to the joint. The bent cap is lowered over the column with longitudinal column reinforcement extending into the cap pocket, and then concrete is placed into the cap pocket completing the connection. While the CPFD specimen utilized the same design as the CIP control specimen, the CPLD specimen had much of the joint shear reinforcement removed to study this connection’s use in lower seismic regions. Vertical stirrups within the joint, joint related stirrups adjacent to the joint, horizontal cross ties, and hoops at the ends of the cap pocket pipe were removed from the CPLD specimen and flexural bent cap reinforcement was reduced. All specimen responses showed similar load-displacement plots with large hysteresis loops. Each specimen reached 95% of its maximum load at approximately a displacement ductility of three (3) (1.62%-1.76% drift ratio) and sustained this load through 6 (3.20%-3.67% drift ratio). All specimens ultimately failed due to plastic hinging of the column eventually resulting in buckling of the longitudinal reinforcement. While strain values within the bent cap flexural reinforcement of the CPFD specimen were significantly larger than the CIP specimen, the CPLD specimen and CIP specimen were similar. Strain values within the cap pocket pipe were relatively low only reaching 48% and 63% of yield for the CPFD and CPLD specimens respectively. Additional analyses were performed, including: displacement decomposition, joint response, and crack pattern observations. Construction of cap pocket specimens revealed the need for construction templates, a flowable concrete mix, and a good system of quality control and quality assurance. The results found within this CE 500 report support the conclusion that the CPFD specimen joint produced emulative response and is recommended for use in high seismic regions. The results also show that the CPLD specimen achieved its performance goals and is an acceptable connection type for limited ductility applications.