Application of Large-Scale Experimental Facilities to the Advancement of Seismic Design and Retrofit of Transportation Facilities

Over the past 30 years, significant research has been devoted to improving the seismic performance of new and existing bridges. The results of this effort can be seen in the ongoing evolution of design specifications for bridges, not only in the U.S., Japan, and Taiwan, but also in other seismically active regions of the world such as China, New Zealand, and Europe. Many of these specifications are now performance-based, driven by the public demand for transportation systems that continue to provide basic levels of service regardless of earthquake size. As a consequence these specifications now set performance criteria for small and large earthquakes (such as minimum levels of functionality, acceptable damage states, and maximum repair times) and imply that, if these provisions are followed, these criteria will be satisfied. However the current state-of-the-art of seismic design is insufficient to make these assurances with confidence for all but the simplest of bridge types, such as a single span bridge on competent soil. Consequently the demand for such performance (for little or no extra cost) has increased the demand for advanced knowledge about the seismic performance of bridges, and is now setting the research agenda. Sophisticated computational tools are widely available for three-dimensional dynamic analysis of nonlinear structural systems, and applications to bridge design are relatively common. However these tools are based on existing notions of structural performance and are consequently limited by existing knowledge and our past experience. But rigorous performance-based design (PBD) requires an understanding of bridge response that is outside the bounds of current knowledge. It also requires that ground motions are known with confidence, including their three-dimensional characteristics and spatial variability. Numerical modeling is a powerful but limited tool and fundamental models are lacking that have the sophistication to satisfy the requirements of PBD. It is believed that the development and calibration of these models requires an experimental effort at a scale that can only now be considered, now that the NEES, NIED and NCREE facilities are on line. In many instances collaborative research using these distributed facilities will accelerate progress, elevate the sophistication of the experiments, and improve confidence in the findings and conclusions.