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OCR for page 46
46 longitudinal load at a pier. The girders may be steel or concrete, This project has identified and prioritized these needs, and and the cap beam may be completely or partially precast. Such those that will provide the quickest and most widespread value connections are likely to be designed as capacity-protected, so are suggested for near-term efforts. that any inelastic deformations are forced to occur in the top In the spirit of addressing the most urgent next steps first, of the column, below the connection. Their expected capacity- the suggested work for immediate research should provide protected behavior renders them different from most of the substantiation of seismic performance and further develop other connections described here. Many configurations are design and construction guidance for the following: possible, and they tend to follow the dictates of the local bridge-building culture. The internal forces must be trans- Bar coupler systems that have already been deployed in ferred from bending in the girders to torsion in the cap beam high seismic regions (i.e., grouted sleeves) and back to bending and shear in the columns. That load path Connections for a complete pier or bent system, inclusive is complex and its integrity can only be investigated with a of top, bottom, and splice column connections using either large-scale test set-up. Consequently, very few such tests have grouted ducts or pocket-type connections at the top and been completed and those that have were on specialized sys- socket-type connections for the bottom. tems. Integral connections have been used in many bridges, with the connection details determined using conventional By addressing the infill effort judged to be remaining for principles of structural design. However, such principles are grouted duct, pocket, and socket connections, the suggested least reliable when load is transferred between many elements work will enable a complete pier system to be deployed with and the geometry of those elements is complex. The system confidence in moderate-to-high seismic areas. Of these, the performance must be understood clearly to ensure that such grouted duct and pocket connections are particularly well connections really can behave as capacity-protected elements. suited for the column to cap beam connection, and the The shortage of system information, combined with extensive grouted duct and socket connection types are suited to the field deployment, place the connection type in the "catch-up" foundation connection. Bar couplers, once verified, could be category. applied anywhere in the structure. Emerging Technologies are a number of technologies that Quasi-static, statically determinate tests are preferred for offer promise of excellent seismic performance, but most are most of the testing because these permit, without ambiguity, not particularly suited to ABC. Examples include specialized the relationships of internal force and displacement to be materials, such as SMAs and engineered cementitious compos- quantified. Such data is necessary to support the development ites (ECCs) to improve toughness and or damping, elastomeric bearings to increase deformability, and so forth. Most of the of design procedures compatible with the AASHTO Guide technologies have not yet been sufficiently developed to permit Specifications, which use displacement-based methodologies. evaluation of their promise for ABC, and only a few prelimi- Beyond such simple testing, eventual proof-of-concept tests nary tests have been conducted to investigate their inelastic should be performed on large-scale subassemblages using response to cyclic loading. Therefore, they are classified here in shake tables. This provides additional confidence in the tech- the "advancement" category. The emerging technologies show nologies under near-actual dynamic conditions. Because we considerable promise for excellent seismic performance, but cannot control the occurrence of large damaging earthquakes, the concepts will require significant additional effort to bring which would provide actual field proof-of-concept, such them to a high TRL and to deployment in the field. This cate- dynamic testing is the next best thing to boost confidence in gory of technology will likely affect bridge seismic design prac- TRL toward the highest level. tice some years in the future. Such systems should be nurtured The next phase of work that is suggested, potentially sev- by continued development effort, but immediate SABC eral years in the future, is comprehensive evaluation and deployment will come from the other technologies that have development of integral connections that form part of the been developed more completely and, in many cases, already load path for longitudinal seismic loading in common with tried in the field either in non-seismic regions or in specialized prestressed girder bridges including the following: innovative projects. Two-stage cap beams with a precast lower drop cap with- out prestress in the connection region Suggested Research Flush-soffit cap beam types where longitudinal post- The objectives of future research for SABC are first, to tensioning may or may not be used address immediate needs for use of ABC in moderate-to-high Innovative connecting approaches beyond those currently seismic regions, then second, to address more promising areas. in use for cap beams

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47 Overall, testing and development of such integral systems There is a higher likelihood of achieving the highest readi- is no less important than development of pier systems. Pier ness level in the shortest time for conventional bridges with system development was prioritized ahead of integral con- the catch-up and infill work that has been recommended. nection development, in part, because such systems have been deployed, they are common throughout the country, Accordingly, an underlying assumption to the recommen- and testing is somewhat less expensive due to specimen size. dations made herein is that the best approach in the near term However, ultimately, both pier and integral testing should be is to focus on bringing the technology with the highest poten- undertaken. tial to benefit the most users to a deployment-ready stage as It is apparent that there is other infill work and much remain- fast as possible. This, in the research team's judgment, is to ing advancement work that falls beyond the scope of the near- bring a bent system to market that can be used with widely term suggestions. The reasons for not suggesting any of that used precast girder conventional bridges. work for immediate priority are as follows: Beyond these near-term goals and to the extent possible, development should continue on technologies that will pro- Adequate development work for even one emerging sys- vide enhanced seismic performance, in addition to enhanc- tem would consume the entire likely budgets available in ing ABC, and that will benefit more specialized bridge types the near term. that are used in smaller numbers.