Improving the design and performance of concrete bridges in seismic regions
- Author(s): Tobolski, Matthew Joseph
- et al.
There are a large number of bridges throughout the United States in need of repair or replacement to resolve structural or operational deficiencies. In replacing these structures, and constructing new bridges, engineers should utilize these construction opportunities to improve the design, construction and performance of new structures. This dissertation focuses on three distinct means for improving bridge systems throughout the U.S. First, improve the seismic response of bridge systems using controlled rocking of bridge piers. Second, improve the constructability of bridges in high seismic regions by development of a validated superstructure system for accelerated construction. Third, improve seismic design through the implementation of a simplified displacement based design approach. Controlled rocking in bridge piers can provide a method of seismic resistance that results in significantly less damage following strong ground shaking. Simplified and detailed design and response prediction methods are presented in this dissertation. These methods were validated against three beam-column experiments. Results from experimental work and analytical prediction models were used to perform a series of nonlinear time history analyses. These results indicate the use of controlled rocking will result in similar ultimate displacement demands with appreciably less residual displacement as compared to conventional systems. Use of precast concrete systems in high seismic regions has been limited due to uncertainties in the performance of connections between elements. A conceptual bridge system was developed, designed and validated through experimental testing to determine the adequacy of the details for seismic applications. This experimental work included the consideration of potential superstructure inelasticity due to relative settlement or vertical motion. Results indicated the capacity of the connection could be adequately predicted using strain-compatibility approaches considering effects of construction staging. Experimental testing validated the system has adequate rotation capacity to accommodate potential demands from relative settlement and vertical motion from relative settlement and vertical motion. A displacement based design procedure is presented which is aimed at the efficient allocation of reinforcing steel in concrete columns for seismic design. This procedure uses established displacement modification factors in combination with mechanics based displacement capacities to derive minimum design resistance require for a column under seismic actions