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A prototype bridge was designed and used for this research project. The methods of design used were representative of existing inverted-tee cap beam bridges for Caltrans and followed current seismic design practice. The prototype structure was used for the finite element analysis and also, a portion of it was used to establish a large-scale test specimen for laboratory testing under simulated seismic loads. Before the design was undertaken, aspects of the bridge had to be decided, including bent style, number of girders and style of girders. A single-column was chosen and the section was used efficiently to create the maximum load at the column-to- cap-beam interface. A multi-column bent would require a much wider superstructure to develop the maximum demand at the column-cap interface when using the same size column. This would not be feasible for experimental research due to the lab space and cost limitations. A circular column was chosen since it is the preferred cross-section in seismic regions as the moment capacity of this column section is the same in any given earthquake loading direction. The superstructure was considered to have five girders to allow for the maximum width for this bridge. Four girders were considered, but the maximum demand on the column would have been less since the superstructure width is limited by the maximum girder spacing of 8 ft., as allowed by the AASHTO LRFD Bridge Design Specifications 3rd Edition for the live loads of the bridge (AASHTO, 2003). For girders, the California I-girder was chosen, as recommended by Caltrans to closely replicate the existing bridges with inverted-tee bent cap. It was decided that the deepest girder should be chosen to create the greatest demand on the girder-to-cap-beam connection. Successfully showing that the new connection has the capacity to withstand this setup, it would follow that the shallower sections would also have an adequate capacity.

The prototype bridge, presented in Appendix A, was designed in accordance to the AASHTO LRFD Bridge Design Specifications 3rd Edition with 2006 Interims and California Amendments (AASHTO) (AASHTO, 2003), as well as the Caltrans Bridge Design Aids (Caltrans, Bridge Design Aids, 1995) for the design of Inverted-T Cap, Caltrans Bridge Design Specifications (BDS) (Caltrans, Bridge Design Specifications, 2003) and Seismic Design Criteria v. 1.4 (SDC) (Caltrans, Seismic Design Criteria, v. 1.4, 2006). Computer software packages

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WinRECOL (TRC/Imbsen Software Systems), Xtract (TRC/Imbsen Software Systems) and Conspan (Bentley Systems, Inc., 2008) were used to aid in the design. A design of the column, cap beam, girder dapped end and slab for the prototype was performed and discussed below. The prototype bridge drawings are given in Appendix A, and the prototype bridge calculations are provided in Appendix B.

Figure 3.1 Prototype Bridge Elevation View 3.2 Model Concept

The test unit was developed based on a 50% dimensional scale of the prototype structure, which represented a typical inverted-T bridge. The specifics regarding the design of both the prototype and the test unit are outlined in Appendix B and in (Thiemann, 2009). Since the behavior of the connection between the girders and the inverted-T cap beam was the main focus of this study, only one column with half of a span on each side was constructed and tested. Therefore, the test unit consisted of a single column with an inverted-T cap beam and a superstructure of five I-girders overlaid with a deck on each side. In order to test both the “as- built connection” as well as the proposed “improved connection” without building two test units, one side of the inverted-T cap beam was constructed using the as-built details while the other was constructed using the improved connection details for the girder-to-cap region. This was possible as the majority of the negative moment contribution was provided through the deck (Hastak, Mirmiran, Miller, Shah, & Castrodale, 2003), which meant that regardless of the type of positive moment connection incorporated, both sides would behave identically when subjected to a negative moment. As a result, based on whether the superstructure of the test unit was pushed or pulled horizontally, it was possible to isolate the effects of the behavior of only one of the

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connection types. Given the orientation of the test unit within the lab at UCSD, the South side represented the as-built condition while the North represented the behavior of the improved connection, as shown in Figure 3.2.

Figure 3.2: Test Unit Orientation

It was decided that two phases of testing would be necessary in order to fully capture the behavior of each connection detail and their influence on the overall behavior of the test unit. The first phase of testing, referred to as Phase 1, was a horizontal cyclic testing of the superstructure. Using two horizontally mounted actuators on each end of the abutment, the superstructure was cyclically pushed and pulled through the following series of increasing system displacement ductility levels, μΔ, until the specimen reached a maximum displacement

ductility of 10. The nature of the test was quasi-static, which meant that the cycles were performed over a very long duration relative to that of a real earthquake. However, cycling the structure at various displacement levels ensured that the test unit was subjected to the same, if not greater, displacement demands than expected from an actual earthquake. The second phase of testing, referred to as Phase 2, isolated the local performance of each connection region. Vertical actuators were used to simultaneously cycle each span of the superstructure up and

As-built connection side Improved connection side

(North)

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down. This allowed the individual local response of each connection detail to be captured at various displacement levels until the ultimate condition was reached.