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32 66'-0" Four traffic lanes @ 12' and sidewalks on each side. 6' wide x 3' deep pc cap beam. WF74G pc girders @ 6' c/c 4'-0" dia. x 25' high pc column. 6'-0" 27'-0" 18'-0" x 18'-0" x 4'-9" CIP footing. Figure 22. Bridge bent considered for time savings evaluation. Most precast connection types have the potential to reduce at pier locations. Thus, pier or bent systems are a primary focus bridge bent construction time by 50% relative to CIP, for seismic use of ABC. although pocket connections only provided about a 25% time savings. Seismic Design The discussion at the workshop on time requirements A key point to understanding ABC in seismic regions is showed that the potential time savings were more closely that it is essential that the designer understand and control related to the characteristics of the bridge bent system as a the seismic design to ensure appropriate seismic behavior. whole rather than to any particular connection technology. This statement applies even more to ABC than it does to the In particular, the choice of precasting the cap beam rather more conventional construction types, because the seismic than casting it in place made the dominant contribution to bridge design codes for conventional construction are set up time savings. to ensure appropriate behavior, even if the designer does not fully understand how all the provisions actually work. Such is not the case with ABC, in part because the connection tech- Evaluation of ABC Bent and nologies vary widely and because specifications for design of Bridge Systems such systems have not progressed to the same point as for The connections summarized above each may be used to conventional bridges. construct a bridge system. Overall the bridge system includes As has been pointed out several times, energy-dissipating superstructure, deck, piers or bents, foundations, and abut- and deformation elements connections must be able to endure ments. Almost any of the bridge elements may be made up multiple inelastic or large deformation cycles without losing of precast or steel members connected with various forms their integrity. In contrast, capacity-protected connections only of connection technologies. These are called Prefabricated need to be capable of developing adequate elastic resistance, Bridge Elements and Systems (PBES). Not all the connections although such resistance is required under cyclic loading. This used to connect such elements require the same ability to classification tool then is useful for focusing the designer's tolerate inelastic deformations in moderate or high seismic attention on the elements and connections that require the zones, and accordingly connection types have been catego- most attention in seismic design. rized as energy-dissipating, capacity-protected, or deformation elements. The connections requiring the most rigorous seismic Bent Systems testing and the most thorough understanding of their behav- ior are the energy-dissipating and deformation elements con- The approach for considering ABC in seismic regions has nections. These connections typically occur in the substructure been one using "building blocks" of connection types. To a

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33 great extent, systems (for example, pier or bent systems) can be constructed using one or more of the connection types previously reviewed. Ultimately, different DOTs or regions of the country might prefer different connection technologies for any of a number of reasons. It is certainly clear that differ- ent bridge construction technologies have been adopted for reasons of regional preference, success with systems, or other reasons. For instance, precast, prestressed girder bridges are often preferred in the Pacific Northwest while other types, such as steel girder bridges or CIP concrete boxes, may dom- inate the market in other states, each being considered the most cost-effective in its own region. A typical prestressed girder bridge is shown in Figure 23. In this bridge, only the gird- ers are precast; however, research sponsored by the Highways for LIFE program is under way to produce a precast bent sys- tem for these bridges that can be used in high seismic regions. As ABC technologies develop, it would be expected that regional preferences might still prevail. This trend can be seen in the emergence of several ABC bent technologies that have been conceived or even deployed to date. For example, the Utah DOT has probably constructed more full ABC bridges in seismic zones than any other agency. An example of one of the bents used along the Interstate-15 corridor near Salt Lake Figure 24. Utah DOT bridge bent system (Culmo 2009). City is shown in Figure 24, where precast columns are con- nected to foundations and cap beams using grout-filled bar couplers (splice sleeves). Other types of PBES substructure and between the top of the column and cap beam (Culmo systems or elements are shown below. 2009). Such connections have been widely used in the non- Figure 24 illustrates a bent system constructed using grouted seismic applications of ABC, but as indicated in the bar coupler splice bar couplers between the base of the column and footing summaries, such connections may require special constraints for use in seismic regions. Figure 25 illustrates the construction of two column pile bents where steel pipe piles passed through sockets formed by corrugated metal pipe similar to that used for the "pocket connections" described previously. The pipes had steel rings Figure 23. Typical precast, prestressed girder bridge Figure 25. Steel pipe pile bent with socket in Washington State. connections (BergerABAM).

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34 welded to them to create roughness that would improve ver- CIP tical shear transfer, then the precast cap was lowered over the Diaphragm pipe piles and the annular space was grouted to form a full Grouted Duct socket connection. The tops of the piles extended into the Connections Precast upper stage cap. Only the lower stage, as shown in the photo, Cap Beam was precast. Pile or trestle bents are common construction types used in many parts of the United States, and this marine Precast application illustrates a viable configuration for use in seismic Segmental Column zones. The use of precast piling is also prevalent in pile bent (to demonstrate construction, and marine applications of grouted duct con- feasibility) Socket nections to cap beams can be adapted for ABC use in land- Connection based environments as well. Figure 26 illustrates another form of making the pier to CIP superstructure connection using a precast pier segment of Footing a spliced girder bridge. The bridge pictured used a CIP lower stage cap beam; however, a precast cap could have been made Figure 27. Highways for LIFE precast bent for to work in this application. The longitudinal force transfer is seismic regions. made via interface shear/torsion similar to connection IC-9 of Appendix F. benefit of such proposals is that, when a contractor chooses Figure 27 illustrates the concept under development in to use ABC technologies, the problems of tolerances and Washington State to develop PBES bent systems for ABC use complex erection procedures can largely disappear, because in high seismic regions. This project is supported by the the contractor "owns" the tight tolerances and can develop FHWA's Highways for LIFE Technology Transfer Program a casting and erection procedure that will work well. For and a demonstration project is currently under contract to low-bid work conditions, this may not be so positive. Much construct this system. Precast columns along with precast depends on the contractor's attitude and willingness to work lower-stage cap beams are used in this project, thus, making with unusual substructure configurations or connections, use of grouted duct, member socket, and integral connection and much depends on the spirit of collaboration between the types. The demonstration project also uses precast, prestressed contractor, engineer, and owner. decked-bulb tees as superstructure. These will be delivered to As described in the Time Savings section, the time savings the site with "ears" at the ends to form stay-in-place forms for expected for a bent system may not be directly attributable to the upper stage of the CIP diaphragm. The objective is to use a certain type of connection, but rather to the elements that are as many precast elements as is reasonable. The examples described above serve to illustrate the range used. For example, it has been demonstrated that more time is of ABC connections and PBES that have been used previously saved by precasting the cap beams than by precasting columns, in bridge bent construction. Much of the research work to even if the connections at the base and top of the columns are date has focused on this type of bent system. PBES elements the same. This illustrates a point that time savings are prima- have also been constructed in the field, and the experience rily a system attribute and not a connection attribute. This also serves to provide data on constructability, durability, and means that savings may be bridge- or job-dependent. time savings. Often the use of precast elements arises out of Other bent systems have been proposed that make use of value engineering or contractor-proposed alternatives. A side ABC technologies. For example, the hybrid systems, contain- ing either a basic combination of prestressed and deformed bar steel, or more elaborate systems that provide further enhanced performance, were discussed earlier in this chapter and in the appendices. Such systems have been developed to the same point as the bent systems using the individual con- nection technologies. The hybrid systems are just that, a sys- tem for the entire bent, rather than a single connection. Various versions of hybrid systems have the potential for pro- viding significantly enhanced seismic performance, as well as potentially providing benefits for ABC. However, the two attributes may not always go together. Some systems may be more complex and take longer to construct than ABC systems Figure 26. Spliced girder bridge with precast pier optimized just to save construction time. Additionally, the segment (BergerABAM). hybrid systems are more appropriate for high seismic zones