A Precast Pier System for ABC in Seismic Regions

Abstract

In this study, a new type of connection is proposed between precast elements in a bridge substructure system. The connection uses structural steel pipes at the column-to-footing and column-to-cap beam connections. For the column-to-footing, the steel pipe is placed inside the column during precasting. During on-site assembly, the other end of the steel pipe slides inside a larger pipe that is placed inside the cast-in-place foundation. Steel plate fins are welded to the column pipe to serve as guides inside the footing pipe. The gap between the pipes are then secured using high strength grout. For better seismic performance, an unbonded length of the pipe is left inside the precast column just above the column-to-footing interface. The unbonded length aims to achieve a higher ductility of the pier system and prevent low-cycle fatigue and strain concentration near the interface. For the column-to-cap beam connection, a similar approach is used. However, in this scenario, both the cap beam and the columns are precast. The pipe connection aims to emulate the conventional cast-in-place behavior, such as the formation of plastic hinges in the columns during an earthquake. It offers good advantages compared to other types of emulative connections such as grouted ducts and splice sleeve connections. The advantages include better tolerance in construction, avoiding damage to the rebars protruding from the precast columns during transportation and assembly, and preventing cracking to the columns during a small earthquake. The experimental program in this study includes testing of large-scale pier systems under quasi-static cyclic loading. Two specimens represent a cantilever pier system and another two represent a bent system. One cantilever and one bent specimen incorporate cast-in-place construction and are intended as a benchmark to compare seismic performance. The other two specimens are constructed using the proposed pipe connection. The paper presents the concept, design, and construction considerations for the proposed pipe connection. Experimental results from testing of the cantilever and bent specimens so far are presented. Based on the outcome of testing, the Idaho Transportation Department (ITD) is planning to use the proposed pipe connection in the construction of an actual bridge on I-15 in southeast Idaho in 2020.