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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
