In recent years, the Accelerated Bridge Construction (ABC) method has received attention in regions of moderate-to-high seismicity. Prefabrication of bridge structural components is a highly effective method in this process and one of the ABC methods for Prefabricated Bridge Elements and Systems (PBES) advanced by the Federal Highway Administration. Joints between such precast concrete components play an important role in the overall seismic performance of bridges constructed with the ABC method. Research has been carried out at the University of Utah to investigate potential ABC joint details for bridges located in high-seismic regions. A connector type, referred to as a Grouted Splice Sleeve (GSS), is studied for column-to-footing and column-to-cap beam joints. Two GSS connectors commonly used in buildings were utilized in this study, as shown in Fig. 1. The column-to-cap beam joints used a GSS connector where one bar was threaded into one end and the other bar was grouted into the opposite end (denoted as FGSS), as shown in Fig. 1(a) and Fig. 1(c). The column-to-footing joints incorporated another type of GSS where the bars were grouted at both ends (denoted as GGSS), as shown in Fig. 1(b) and Fig. 1(d).
Three precast alternatives in addition to one conventional cast-in-place half-scale model were constructed for each category, as shown in Fig. 2; the column-to-cap beam joints were tested upside down. The GSS connectors were placed in the column base (GGSS-1) or column top (FGSS-1) in the first alternative. The location of the GSS connectors changed to the top of the footing (GGSS-2) and bottom of the cap beam (FGSS-2) to study the performance of the joints when the GSS connectors were outside the plastic hinge zone of the column in the second alternative. The dowel bars in the footing and the cap beam were debonded over a length equal to eight times the rebar diameter (8db) for the third alternative in both categories, while the GSS connectors were embedded in the column base (GGSS-3) or column top (FGSS-3). The last specimen type was the cast-in-place joint, in which continuous bars from the footing and cap beam were used to build the columns with-out bar splices (GGSS-CIP and FGSS-CIP).
Experimental results under cyclic quasi-static loading showed that the performance of all joints was satisfactory in terms of strength and stiffness characteristics. However, the hysteretic performance and displacement ductility capacity of the specimens were distinct. Improved seismic response was observed when the GSS connectors were located inside the footing (GGSS-2) and the cap beam (FGSS-2) rather than the corresponding column end. The debonded rebar zone enhanced the ductility level and the hysteretic performance of the joints. This technique was found to be highly effective for the column-to-footing joint (GGSS-3), as shown in Fig. 3. As expected, the cast-in-place joints performed the best.
Even though AASHTO Specifications currently do not allow the use of connectors in the plastic hinge region, all joints tested in this research demonstrated acceptable ductility for moderate-seismic regions and some joints demonstrated acceptable ductility for high-seismic regions. The GSS connectors studied in this research were promising, especially when considering the time-saving potential of joints constructed using ABC methods; however, the different hysteretic performance and reduced displacement ductility of various alternatives com-pared to the cast-in-place joints must be accounted for in design.
Acknowledgments: This study is described further, including recent reports, on the TPF-5(257) website. The authors acknowledge the financial support of the Utah, New York State and Texas Departments of Transportation, and the Mountain Plains Consortium. The authors also acknowledge the assistance of Joel Parks, Dylan Brown, and Mark Bryant of the University of Utah.
This guest post was written by Chris P. Pantelides, Ph.D., University of Utah, M.J. Ameli, University of Utah, and Jason Richins, S.E., Research Engineering Manager and was originally published in the Research Newsletter.