Civil Engineering Association

SEISMIC VULNERABILITY OF OREGON STATE HIGHWAY BRIDGES

Hundreds of Oregon bridges remain vulnerable to earthquake damage. Although 15-20 earthquakes of magnitude M>3.0 are felt each year in the Pacific Northwest, modern Seismic Design Specifications were not available or used for bridge design until early 1990. With a majority of state owned bridges designed and built between 1950 and 1980, the state of Oregon would face a devastating post earthquake situation if a major event occurred in the state. The Oregon Department of Transportation (ODOT) has begun a study to define the magnitude of the problem by evaluating the vulnerability of state highway bridges in western Oregon. This report is intended to be a first step in a comprehensive look at seismic risk to transportation systems that could include slides, fill slopes,
local roads and bridges, and supply lines, such as fuel depots, electricity, water and sewer lines. This report marks the culmination of two years of study jointly conducted by ODOT and Portland State University. The study makes use of a computer program called REDARS2 that simulates damage to bridges within a transportation network. It can predict ground motions for a speci c location and magnitude of earthquake, resulting bridge damage and the cost of the
damage, as well as the cost to the public for traffic delays due to detours around damaged bridges. Estimated damage and delay costs are presented for major highways in Western Oregon, where most of the earthquake
damage is predicted to occur.