Experimental and Analytical Seismic Studies of Bridge Piers with Innovative Pipe Pin Column-Footing Connections and Precast Cap Beams
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The use of prefabricated structural elements is an integral part of many accelerated bridge construction (ABC) efforts. Connections of these prefabricated elements to the rest of the structural system is critical to the performance of the structure under service loads and extreme events such as earthquakes. Two types of novel joints were developed in this study: 1) base pipe pin connections to substantially reduce the moment transfer between the column and footing, and 2) pocket connections to provide structural continuity at column-cap beam joints. The pipe pin consists of two steel pipes to transfer shear and a tension member to transfer uplift forces. Pocket connection is formed by extending the column into a pre-fabricated pocket in a precast cap beam and grouting the space between the column segment and the pocket. The primary objective of this research was to investigate the seismic performance, response, and behavior of base pipe pins for both cast-in-place (CIP) and precast construction, to study the performance of column-cap beam pocket connections to be utilized in ABC, and to develop a reliable design guideline for base pipe pins. This research was comprised of comprehensive experimental and analytical studies. The experimental portion of the study was conducted at the University of Nevada, Reno Large Scale Structural Laboratory including three sets of tests: 1) cyclic loading test of a large-scale two-column bent model, and 2) two direct pull tests of CIP and precast pipe pin connections. The bent model was composed of a precast engineered cementitious composite (ECC)-concrete column, a conventional CIP reinforced concrete column, a precast cap beam, and two single footings. The columns were connected to the footing and cap beam utilizing pipe pin and pocket connections, respectively. Direct pull tests were carried out to investigate the failure mode of the pipe pins under direct tension and determine the ultimate tensile capacity of the pins. The proposed pipe pin connections were found to be successful even under high drift ratios. Test results revealed that pipe pins needs to be designed for shear forces that exceed the column design shear due to reversed friction under large base rotations. Direct pull tests of the pipe pins showed that the dominant failure mode of the connection under pure tension was rupture of the tension member and all the other connection elements remained damage free. The pocket connection using corrugated steel pipes with a column embedment length of 1.2 times the column diameter performed well in forming the plastic hinge when conventional concrete was used in the embedded region. However, longitudinal bars in the precast column with embedded ECC debonded at 4% drift ratio. The analytical study consisted of 1) elaborate finite element (FE) modeling of the pipe pin connections and footings under direct tension, 2) FE study of the two-column bent, and 3) analytical modeling of pipe embedded in the footing (pipe shear key). ABAQUS and OpenSees were used in the analyses. The analytical models were evaluated based on correlation with experimental data, and were then used to investigate the effects of different parameters on the seismic performance of pipe pins.Results of the parametric studies along with the experimental observations led to an iterative procedure to determine seismic demands and methods for designing pipe pins. This was followed by development of design and detailing methods and illustrative examples.