All ETDs from UAB

Advisory Committee Chair

Chrostopher Waldron

Advisory Committee Members

Jason Kirby

Talat Salama

Document Type

Thesis

Date of Award

2012

Degree Name by School

Master of Science in Civil Engineering (MSCE) School of Engineering

Abstract

The issue of increasing the gross vehicle weight limit on the interstate highway system has been debated on the local and federal levels. The driving forces for and against this topic cover a broad spectra ranging from economic benefits to public safety. The University Transportation Center of Alabama is sponsoring this study assessing the force effect that bridges experience when travelled by vehicles with a 97,000-lb gross vehicle weight (GVW). The maximum internal shear and moment caused by two proposed trucks (97-S and 97-TRB) are compared to effects from three base models: design live loadings from the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications and AASHTO Load and Resistance Factor Design (LRFD) Specifications, and the envelope from five potentially critical Alabama legal loads. Hypothetical simple span bridges and two-span continuous bridges with a 1:1 span ratio are analyzed with each load model, providing data that correlates to the impact that increased truck weight has on bridges. Results show that the shorter 97-S causes greater shear and moment compared to the 97-TRB on all simple spans and a large percentage of the continuous span bridges investigated. The design live loading issued in the AASHTO Standard Specifications does not generate adequate force effects that fully envelope the effects from 97-kip vehicles. Depending on span length and bridge type, both proposed models will exhibit force effects above those from the envelope of five Alabama legal loads. However, effects initiated by the LRFD model envelope all shear and moment effects of both 97-kip trucks on each of the two bridge types. It is concluded that LRFD methods represent significant benefits to bridge design practices concerning the implementation of heavier trucks on the interstate highway system. Additionally, the deck reinforcement specified by the Alabama Department of Transportation (ALDOT) Bridge Bureau's standard slab detail is checked using the LRFD Specifications and the 51-kip tri-axle load of the 97-kip vehicles. For several girder spacings, it is determined that the primary reinforcement utilized in ALDOT's standard slab design does not meet the strength requirements of AASHTO LRFD.

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