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9 region and girders without web stiffeners. Two conditions for The first of the three systems was not selected in order not to the cap beam were also considered--a conventional reinforced duplicate the work started at UCSD (see Section 2.1.2 above). concrete cap beam and a post-tensioned cap beam. Four com- The second system was excluded because multi-column piers ponent tests were conducted under longitudinal seismic load- have not been used in the past and also because the results of ing to investigate several possible combinations of the above- studying the connection of a single-column pier to the super- mentioned parameters. Based on the test results, an integral structure can be applied to the design of the connection of the bridge system composed of stiffened steel girders and a post- columns of a multi-column pier. The third system was selected tensioned cap beam was selected for system level investigation. for further study. The system test was conducted at 40-percent scale and The details of the selection process are presented in showed that the proposed integral bridge system with stiff- Appendix C (provided on the accompanying CD-ROM). ened girders and post-tensioned cap beams would provide ductile seismic response. In the test unit, the plastic hinge 2.3 PROTOTYPE BRIDGE CONFIGURATION was fully developed in the column while the superstructure AND DESIGN exhibited essentially elastic response. Concrete box-girder bridges and precast concrete and steel Following is a summary of the description of the prototype girder bridges designed generally with post-tensioned pier bridge and its design. More details on the prototype bridge caps were the subjects of these articles, most of which dis- are provided in Appendix D (provided on the accompanying cuss the application of integral pier bridges in non-seismic CD-ROM). regions. Review of these articles made it apparent that inte- gral pier concrete bridges have gained increasing popularity both in the United States and overseas since the mid-1970s. 2.3.1 Configuration At present, several state DOTs use the integral pier concept for new bridges. Given the benefits of steel girder integral A continuous, two-span bridge with a single-column pier bridges in seismic regions, an investigation of this bridge reinforced-concrete intermediate pier, steel box-beam pier concept with emphasis on seismic issues was needed. cap, and steel girders as shown in Figure 2 was selected as the prototype bridge. The prototype contains an integral con- nection between the column and the pier cap and integral con- 2.2 FEASIBLE INTEGRAL PIER CONCEPTS nections between the girders and pier cap and is simply sup- ported at the abutments. Each span of the prototype bridge To identify integral connection concepts for this study, the was 30.5 m (100 ft.). The column height measured from the research team studied the connection concepts used in the past bottom of the pier cap to the top of the footing was taken as and developed several other systems. In total, 14 different pier 12.2 m (40 ft.). The bridge was assumed to have four girders cap systems were examined. The attributes of each pier cap spaced at 3.050 m (10 ft.). system were determined, and the systems were grouped based A compartment centered above the column and bounded on the number of columns per pier, type of girders, the need by the two box-beam webs and internal diaphragms aligned for shoring during construction, and the pier cap material. In with the interior girder was assumed to be filled with con- addition, two main types, concrete and steel, of the integral crete. The column longitudinal bars were assumed to pass connections were examined. A detailed description of all sys- through holes in the bottom flange of the pier cap and to be tems examined and their attributes is provided in Appendix C anchored in the concrete inside the cap. Shear studs welded (provided on the accompanying CD-ROM). to the inside of the pier cap were assumed to transfer the col- Criteria were developed to assist in selecting a system for umn forces from the concrete inside the cap to the cap itself. further detailed studies. These selection criteria were based on listing several desirable features and giving each of the 14 systems considered a score for each feature. Some of the 2.3.2 Design features considered were related to construction and others were related to the long-term performance and economy of The bridge superstructure and substructure components the system. Several practicing engineers participated in the were designed in accordance with the 1998 AASHTO LRFD selection process and the scores were averaged. Bridge Design Specifications (1). In addition to traffic loads, The systems with highest score were as follows: the bridge was designed for seismic loads as a bridge in Seis- mic Zone 4, assuming a ground acceleration of 0.4 g. Steel I-girders on single-column piers and post-tensioned The seismic design of the prototype structure was based on concrete pier cap, two criteria: (1) the 1998 AASHTO-LRFD provisions as rep- Steel I-girders on multi-column piers with columns resentative of typical design procedure and (2) the ATC-32 located under each girder, and recommendations in consideration of current seismic design Steel I-girders on single-column piers and steel box-beam philosophy. In addition, it was decided that a minimum rein- pier cap. forcement ratio of 2 percent would be considered in order to