Pacific Earthquake Engineering Research Center (PEER) - Lifeline Partnership Phase 3

Earthquakes produce strong ground motions (shaking, fault offsets) that can cause bridge collapse or other unacceptable loss of function. It is estimated that nearly $1 billion annually of Caltrans' bridge designs are governed by seismic loading criteria. Uncertainties in ground motions used for engineering design can lead to either over-conservative and overly-expensive structures or under-conservative facilities that may perform poorly in the next major earthquake. The Pacific Earthquake Engineering Research Center (PEER) Lifelines program has already made tremendous advances in the fundamental understanding of the strength, distribution, likelihood, and location of damaging ground motions. This task allows for continuation of that effort and partnership of experts. It has forged consensus among widely varied scientific opinions, and has produced a suite of "Next Generation Attenuation (NGA) attenuation relations that are now being adopted nationally at the highest organizational levels. The current NGA models yield predictions for median ground motions with respect to azimuthal orientation. It is well recognized that near-source ground motions applicable to most California Department of Transportation (Caltrans) bridges include effects such as "directivity" that vary predictably with bridge orientation. The partnered organizational framework now existing within the PEER-Lifelines program is very well positioned to allow rapid progress toward developing refined NGA models that incorporate directivity and other new knowledge.