Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
1 Accelerated bridge construction (ABC) utilizes rigorous planning, new technologies, and improved methods to expedite construction. Prefabricated columns and their connections to adjoining bridge members (cap beams, footings, pile caps, and pile shafts) are the most critical components of ABC in moderate- and high-seismic regions. Recent studies on the seismic performance of various types of ABC column connections have demonstrated the feasibility of ABC in such regions. Some gaps remain. To help expand the utilization of ABC in all seismic regions, seismic design specifications are needed. The main objective of NCHRP Project 12-105 was to develop proposed AASHTO displacement-based design and construction specifications for the implementation of ABC column connections in moderate- and high-seismic regions. The project was focused on three precast column connections: (1) mechanical bar coupler connections, (2) grouted duct connections, and (3) pocket/socket connections. Several tasks including experimental and analytical programs were undertaken in this project to achieve the aforementioned goal. A state-of-the-art literature review of recent experimental and analytical studies on the seismic response and constructability of the three types of ABC column connections was performed. A survey of state departments of transportation, federal agencies, and consulting engineers was conducted to obtain information about their experience, preferences, and past and future utilization of ABC connections. Subsequently, the results of the literature review and survey were synthesized and knowledge gaps were identified. Additional experimental and analytical studies of the highest priority, which were necessary before seismic design specifications could be developed for the three types of precast column connections, were identified. An experimental program that included the testing of 43 specimens was executed to fill some of the knowledge gaps identified for the three ABC column connections. The test program included tensile testing of 30 coupler specimens, pullout testing of 12 specimens with bars anchored in grouted ducts, and slow-cyclic lateral load testing of a half-scale bridge column incorporating grouted sleeve couplers. ASTM A706 No. 10 reinforcing steel bars were utilized in all 43 test specimens to generate data for a realistic bar size used in the field. An extensive analytical investigation was carried out to fill the remaining knowledge gaps identified for the selected types of ABC column connections. For each analytical model, test data obtained in this project or from the literature or both were used to validate the proposed model. For couplers, a set of new acceptance criteria for seismic mechanical bar splices in the plastic hinge of bridge columns was presented, and a material model was proposed for all types of tension-compression couplers. For mechanically spliced columns, a comprehensive parametric study was performed to quantify the effect S U M M A R Y Proposed AASHTO Seismic Specifications for ABC Column Connections
2 Proposed AASHTO Seismic Specifications for ABC Column Connections of couplers on the seismic performance of mechanically spliced bridge columns. Simple design equations were presented, including a modified equation for plastic hinge length to include the coupler effect in the design of bridge columns. For grouted duct connec- tions, all available test data were collected and then a design equation was proposed to determine the embedment length of deformed bars in grouted duct connections. Sub- sequently, detailed finite element analyses were carried out to determine the minimum size of column adjoining members incorporating grouted duct connections and pocket connections. On the basis of the findings of the experimental and analytical studies, design and con- struction specifications were proposed for mechanically spliced bridge columns, columns incorporating grouted ducts, and columns using pocket/socket connections. Instead of developing a stand-alone document for the design of each of the selected ABC column con- nections, the research team prepared new specifications in the form of an appendix to the AASHTO Guide Specifications for LRFD Seismic Bridge Design with reference to the relevant sections of that volume. Furthermore, a standard testing method including acceptance criteria and a material model was proposed for seismic mechanical bar splices. Finally, five design examples were developed to illustrate the implementation of the proposed speci- fications. One example was a conventional cast-in-place bridge to serve as a benchmark model. The same bridge was redesigned in the other examples, each of which implemented a different type of ABC column connection. This report includes six chapters and four appendices that summarize the findings of the individual tasks. Appendices B and C address the main objectives of the project, and Appendix D presents the design examples. Appendix A presents the survey and a sum- mary of its findings. The reportâs six chapters provide background, experimental and analytical findings, and supporting information used in the development of the proposed guidelines. Overall, NCHRP Research Report 935 aims to facilitate the field deployment of three types of connections for precast columns by providing introductory information, design and construction specifications, and examples.
