Seismic retrofit benefit considering statewide transportation assessment.
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2015-06-01
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Abstract:The purpose of this study was to identify and demonstrate a methodology to prioritize bridges for
retrofit in the State of Oregon. Given the limited resources available, retrofitting all vulnerable bridges in the foreseeable
future would not be impractical. Instead, a retrofit strategy needs to be developed to prioritize the inventory and enumerate
the retrofit cost. In this study, a prioritization methodology used a holistic assessment of overall roadway system to consider
highway route segments, rather than individual bridges. The overall assessment was based on a cost-benefit analysis
including retrofit cost, expected economic loss (with or without retrofit) and social loss caused by system wide travel time
delays.
A review of 2010 ODOT bridge inventory suggested that a continuous concrete girder bridge (CCGS) with three
spans could be utilized to represent a sizeable portion of vulnerable inventory for Oregon highways bridges. After reviewing
several potential retrofit measures, carbon fiber composite material was selected for retrofit of vulnerable columns
representing those built from the 1950s to mid-1970s. Four full-scale typical square columns were tested to failure. The
results showed that despite the intentionally selected square geometry of the reinforced concrete columns, the CFRP
composite material showed to be an effective retrofit measure and could be deployed for to address this deficiency.
The software package REDARS2 was used for seismic risk analysis (SRA) of the highway network in this study. This
platform was adopted to simulate the impact of scenario earthquakes in an effort to assess the expected benefit considering
direct bridge costs as well as social costs from traffic induced delays resulting from seismic retrofitting of a particular bridge
type. The assessment considered three scenario Cascadia Subsection Zone earthquakes of magnitudes 9.0, 8.5 North, and,
8.5 South. The study area included all highway routes west of the I-5 corridor, highway routes in the Portland area, the
entire length of US-101 and extending partially east on I-84 Columbia River Highway. Due to the considerations of a single
bridge type and other limitations identified in the seismic analysis software (REDARS2), the retrofit assessment outcomes
should be regarded as a first order estimate.
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