The “Next Generation of Ground-Motion Attenuation Models” (NGA) project is a multidisciplinary research program coordinated by the Lifelines Program of the Pacific Earthquake Engineering Research Center (PEER), in partnership with the U.S. Geological Survey and the Southern California Earthquake Center. The objective of the project is to develop new ground-motion prediction relations through a comprehensive and highly interactive research program. Five sets of ground-motion models were developed by teams working independently but interacting with one another throughout the development process. The development of ground-motion models was supported by other project components, which included (1) developing an updated and expanded PEER database of recorded ground motions, including supporting information on the strong-motion record processing, earthquake sources, travel path, and recording station site conditions; (2) conducting supporting research projects to provide guidance on the selected functional forms of the ground-motion models; and (3) conducting a program of interactions throughout the development process to provide input and reviews from both the scientific research and engineering user communities. An overview of the NGA project components, process, and products is presented in this paper.

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Field reconnaissance reports reveal the seismic vulnerability of bridge abutment foundations. To reduce the time and cost of postearthquake repair, modern seismic design specifications allow abutment backwalls to fracture before the supporting abutment foundations reach their maximum strength. This design strategy enables abutment backwalls to function as a fuse, thus protecting the abutment foundations from experiencing excessive forces and damage. This paper introduces a new abutment modeling scheme to capture the shear fracture mechanism of straight backwalls in seat abutments. To this end, a backwall connection spring is developed and incorporated into a spring system that simulates the behavior of various abutment components. The importance of considering the backwall fracture is examined by reviewing conventional modeling methodologies for abutments and building companion numerical models. Static pushover and incremental dynamic analyses (IDAs) were conducted for two bridges (single‐ and two‐span) modeled by both the proposed and conventional abutment modeling schemes. Moreover, component‐level fragility curves are developed using IDA results. The comparisons show that the conventional abutment modeling schemes significantly overestimate abutment foundation damage and underestimate the likelihood of deck unseating, column damage, and bearing displacement in the passive direction. Conversely, the proposed modeling scheme is able to capture the essential seismic responses of various components in seat abutment bridges. The consideration of backwall fracture in the modeling of abutment components enables a more rational seismic response assessment of bridges with backwalls, which are likely to be damaged during earthquakes, particularly for bridges which are seismically designed to protect abutment foundations.