Report No.: CCEER-06-2
Title: Large-Scale Experimental and Analytical Studies of a Two-Span Reinforced Concrete Bridge System
Authors: Nathan S. Johnson, M. "Saiid" Saiidi, and David H. Sanders
Date: March, 2005
Sponsoring Agency: National Science Foundation (NSF)
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557
A quarter-scale, 67 ft (20.5 m) long asymmetric reinforced concrete bridge model with two-spans supported on three, two-column piers was tested using the shake table system at the University of Nevada Reno. In addition, extensive analytical studies were conducted. The shake table testing was part of a multi-university research project utilizing the Network for Earthquake Engineering Simulation (NEES) to investigate the effects of soil foundation structure interaction. The shake table testing objective was to study the response of a reinforced concrete bridge model subjected to mostly transverse earthquake excitations. This included the effects of in-plane rotation irregularities on distribution of forces among different piers and the interaction of different components of the bridge.
Upon completion of testing, in depth analytical modeling was conducted to evaluate the accuracy of conventional methods in reproducing the bridge model response and to develop a model for further study. Three aspects of bridge system response were studied utilizing the analytical model. 1) Performance of the bridge compared to the design performance objectives. 2) The effect of differences between the target and achieved shake table motions on the progression of damage in the bridge. 3) Investigation of the system effect, comparing the system and response of individual bents as well as the response of several other bridge models.
Contemporary analytical methods were accurate in determining the response of the flexurally dominated system up to bent failure. The NCHRP 12-49 design methodology was shown to satisfy earthquake performance requirements. Incoherency of achieved table motions did not affect failure progression of the bridge; however, it was affected by acceleration inconsistencies.
The introduction of higher modes and interaction among the bents (system effect) changed the amount of damage the bents underwent compared to the damage they would have experienced had they been individually tested. A simple irregularity index was found to be a good indicator to identify whether the system will have an effect on the bents. The failure progression of the bridge model and the analytical comparisons suggested that the reserve capacity from varied column heights could provide a beneficial substructure redundancy.