Date of Graduation

2001

Document Type

Thesis

Degree Type

MS

Committee Chair

Karl E. Barth

Abstract

In the early 90’s a collaborative effort between the American Iron & Steel Institute, the US Navy, and the Federal Highway Administration began the development of high performance steel (HPS). HPS70W is the product of this effort and is currently being employed in bridge design. The benefits of this steel are higher fracture toughness, improved welding characteristics, and enhanced weathering characteristics. However, HPS70W has an increased material relative to traditional bridge steels. Because of the increased cost, there is a need to investigate the economical use of HPS70W in design. A few studies have been performed to explore this issue and the benefits realized by weight savings and reduced fabrication costs, which may offset the increased material costs. In spite of the previous studies, there is still a need for more work on the issue of where HPS70W is most economical in steel bridges. The primary objective of this study was to investigate the economy of HPS70W in steel bridge design using various span lengths, girder spacings and yield strength combinations. Three extensive parametric studies were performed and examined for weight, performance, deflection, and cost. These studies include: (1) a parametric study focused on using HPS 70W in conjunction with the Load Factor Design Specifications, (2) a study focused on investigating the use of HPS 70W in simply-supported short span bridges using the Load and Resistance Factor Design [LRFD] specification, and (3) a cost study focused on using LRFD for a given 3 span configuration. Results from this work indicate that the most economical use of HPS70W is a hybrid girder configuration with all 70-ksi bottom flanges and 70-ksi steel in the top flange of the negative moment region. Additionally, studies with variable girder spacings indicated that as a girder line is removed, all yield strength configurations realized weight and cost savings. Finally, the use of the current AASHTO live-load deflection limits required increased the section requirements of the girder, specifically at higher span-to depth-ratios and for sections incorporating HPS 70W.

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