United States Department of Transportation
i
Assessment and Evaluations of I-80 Truck Loads and Their Load Effects: Phase 2: Service
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2020-04-01
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[PDF-797.89 KB]
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Edition:Final Report, March 2018 to May 2020
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Abstract:The research objective is to assess the performance (in terms of AASHTO design expectations for serviceability) of bridges along the Interstate 80 (I-80) corridor for Wyoming’s truck traffic. Wyoming’s I-80 carries a large volume of cross-continental and large energy industry trucks compared to many states. Moreover, frequent weather closures position trucks side-by-side and end-to-end for miles. These vehicles then travel as a convoy once the road opens. Wyoming’s unique truck traffic and traffic patterns potentially create larger demands on bridges than those considered in the development of the AASHTO LRFD Bridge Design Specifications. These characteristics may also be true for other states that contain unique traffic features. Reliability studies and live load factor calibration were performed in this study using a database of in-service Wyoming bridges. This database, consisting of 112 steel bridges and 60 prestressed concrete bridges, was used to determine modified Service II and Service III live load factors to maintain adequate reliability against exceeding serviceability limit states. The results confirm that the current live load factor of γL = 1.30 does not meet the serviceability expectations in the AASHTO Service II limit state (structural steel yielding) for Wyoming traffic on I-80. The results also confirm that the current live load factor of γL = 0.80 does not meet the serviceability expectations in the AASHTO Service III limit state (prestressed concrete cracking) for Wyoming traffic on I-80. Based on the I-80 weigh-in-motion (WIM) vehicle load characteristics that create load effects for Service II and Service III limit states, the reliability indices do not meet the target reliability in the AASHTO LRFD Specifications. Raising the design live load factors, γL, directly and fairly uniformly increases reliability indices. An increase in γL for Service II to 1.45 (from 1.30) and an increase in γL for Service III to 1.00 (from 0.80) increases all of the reliability indices to more closely match the reliability indices expected with the AASHTO LRFD Specifications.
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