Saad, Sander, and Buckle 2012
In this paper, the seismic performances of curved bridges with controlled rocking foundations are evaluated. Using documented analytical and experimental studies of buildings subjected to controlled rocking, the concept was applied to a three-span curved bridge which is supported on two single column bents and two end abutments. The purpose of the experiment was to compare distribution of the demands on a superstructure and the overall displacement to systems without rocking.
System Concept
Using SAP 2000, five bridges were modeled in the parametric study. Weight and length of each model was held constant, while the horizontal curvature varied. Each model consisted of three spans with two single column bents. Frame elements were used in modeling the bridge superstructure rather than a finite element model to reduce time-history analyses computation time. The effects of rocking were analyzed by varying the foot sizes.
A gap link element with zero gap was used to models the soil beneath and around the footing. This element contained a lumped stiffness of the soil in compression and free in tension, which allowed uplift of the footing. A nonlinear time-history analyses based on the Northbridge Earthquake record was used for experiment input motion.
Experimental Study, Results, and Discussion
Using the Northbridge Earthquake record, preliminary results suggested smaller footing sizes had increased footing uplift versus larger ones, with resulted in less damage to the columns. It was also found the amount of energy dissipation decreased with footing size, while overall bridge displacement increased. This indicated that both column and overall bridge performance are affected by the rocking behavior.
Reference
Saad, A., Sanders, D. H., and Buckle, I. (2012). “Impact of Rocking Foundations on Horizontally Curved Bridge Systems Subjected to Seismic Loading,” Proceedings of the Structures Congress 2012, Chicago, IL, March 29-31.