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Development of Earthquake-resistant Precast Pier Systems for Accelerated Bridge Construction in Nevada
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The Nevada Department of Transportation (NDOT) has used to a limited extent prefabricated bridge elements for accelerated construction of single-span bridges. For NDOT to expand its accelerated bridge construction (ABC) program, reliable and practical earthquake-resistant elements and connections need to be developed for bridges with two or more spans. The main objective of the present study was to address this need utilizing a comprehensive literature search on different types of ABC connections, a rating system for evaluation of available connections, and experimental and analytical studies. Various types of bridge column moment and pin connections and superstructurecap beam-column connections suitable for use in ABC were identified and reviewed in detail. To evaluate the ABC bridge column connections suiting the needs of NDOT, a rating system was developed taking into account the level of development, seismic performance, and non-seismic parameters associated with each connection type. All the connections were rated compared to reference cast-in-place connections. The seismic performance of the top-rated connections was investigated in shake table testing of a one-third scale, two-column pier model. Columns were connected to the footing using moment pocket connections and to the cap beam using a combination of the rebar hinge and pocket detail for one column, and a new generation of pipe pins (labeled as one-piece pipe pin) and pocket detail for the other. The one-piece pipe pin connection is composed of an in-filled steel pipe with welded studs on the surface embedded in the column and the adjoining member. The pier model was tested to failure under increasing amplitudes of the Sylmar convertor station ground motion record simulated on a shake table. The proposed pocket connections, pipe pin, and rebar hinge were found to be successful even under high drift ratios. Moreover, the precast cap beam remained elastic and damage free during the entire testing. To investigate the effects of important variables on the response and behavior of pipe pins, a comprehensive parametric study was conducted analytically on a reference subsystem using OpenSees. The reference subsystem was a fixed-fixed single-column pier in which the column was connected to the cap beam using a one-piece pipe pin. The parameters included in the study were: the axial load index, debonded length of the pipe in the column and adjoining member, pipe diameter, embedment length of the pipe in the column and the adjoining member, and the compressive strength of the material around the pipe. It was found that limiting the minimum plastic moment capacity of the infilled-pipe and debonding of the pipe in the column can reduce the strain demand in the pipe. The analytical results were utilized to develop a simple and practical analytical method for modeling pipe pins. Results of the parametric studies together with the experimental observations led to a method for seismic design of pipe pins followed by several detailing recommendations and an illustrative example.
Report No. CCEER-17-03