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7 To perform this task, a significant review and survey of Lateral Response state departments of transportation (DOTs) and engineers was conducted to identify prior uses of precast bent caps Conventional Rocking throughout the world. During this survey, more than 60 proj- ects that used precast bent caps for all levels of seismicity Jointed Hybrid were identified in 23 U.S. states, Puerto Rico, New Zealand, Europe, and Saudi Arabia. However, the majority of these previous applications were in regions subjected to minimal seismic actions, and almost all details were for nonintegral applications. In addition to gathering information regarding prior implementation, the survey was aimed at obtaining insight into why these details have not been widely used. Engineers and agencies expressed reservations about using precast bent caps in seismic regions because of the lack of prior research and performance data for these systems. Many state DOT officials indicated that they would not allow the use of precast bent caps for higher seismic regions without validated design methodologies. Various other concerns were voiced regarding potential fabrication complexities as seismic demand increased Figure 1.4. An overview of idealized lateral response due to heavy congestion at connection regions. Many fabri- for various column systems (5). cators did indicate that the use of post-tensioning would be a potentially advantageous way to reduce this congestion and reduced structural damage when designed using a rationally provide a more constructible system. From a construction founded approach (5). The combination of unbonded post- standpoint, many contractors indicated that they have reser- tensioning and mild reinforcement is termed "hybrid systems" vations due to the potentially small tolerances that would be throughout this report and is depicted in Figure 1.4. Tobolski required to erect these precast systems. Many persons indi- (5) provides detailed information regarding the design and cated that the required tolerances are achievable, but require performance of hybrid systems for bridge applications. increased care during construction that would in turn result in construction cost increases. 1.2 Implications for Bridge Based on the review of previous details and seismic research Design and Construction along with the input from industry, a variety of connection concepts were developed and evaluated for expected seismic The results published in this report summarize a com- performance, constructability, durability, advantages, and prehensive research program that was aimed at the ultimate disadvantages. During this effort, the following nonintegral implementation of precast bent cap systems throughout U.S. connection types were developed, as described in Tobolski seismic regions. The analytical and experimental program et al. (10): conducted served to validate the expected performance of a variety of precast bent cap details when subjected to seismic Grouted duct connection loadings. The results presented herein facilitate an under- Bolted connection standing of the design and construction efforts required for Grouted sleeve coupler connection safe and economical implementation of precast bent cap sys- Cap pocket connection tems throughout the United States. Symbols and variables Welded connection used throughout this document follow standard AASHTO Partially precast shell connection convention. Conventional hybrid connection Concrete filled pipe hybrid connection Hollow dual shell hybrid connection 1.3 Key Results from Initial Report The first step in the research program was to develop Additionally, a variety of precast, integral bent cap systems promising precast bent cap connection and system details were presented. However, based on significant interaction with for use throughout the United State's seismic regions (10). the NCHRP Project 12-74 panel, a future integral connection