Expanding the Applicability of Press-Brake-Formed Tub Girders Through the Extension of the Maximum Span Length and the Evaluation of Pier Continuity

Abstract

The Short Span Steel Bridge Alliance (SSSBA) is a group of bridge and buried soil steel structure industry leaders who provide educational information on the design and construction of short-span steel bridges in installations up to 140 feet in length. Within the SSSBA technical working group, a modular, shallow press-brake-formed tub girder (PBFTG) was developed to address the demand in the short-span steel bridge market for rapid infrastructure replacement solutions. PBFTGs consist of modular, shallow, trapezoidal boxes fabricated from cold-bent structural steel plate. A concrete deck, or other deck option, may be placed on the girder, and the modular unit can be shipped by truck to the bridge site. PBFTGs perform exceptionally well in simply supported, right, straight bridges utilizing current American Association of State and Highway Transportation Officials Load Resistance and Factor Design Bridge Design Specifications’ (AASHTO LRFD BDS) Live Load Distribution Factors (LLDFs). The specifications limit the use of PBFTGs outside of these scenarios, despite the expectation they would perform well in a variety of other situations. More research and data are necessary to validate the current limitations in the AASHTO LRFD BDS and increase the applicability of PBFTGs into continuous spans and skewed bridges. The scope of this project was to expand the applicability and usability of the PBFTG system. This was performed in several stages. First, a complete understanding and background of PBFTGs, LLDFs, box-girder capacity determinations, link slabs, and the AASHTO LRFD BDS was provided. This understanding and background of the restrictions placed on PBFTGs provided insight when developing the methodologies to overcome these restrictions. Next, analytical modeling techniques were developed and refined utilizing complicated geometry and nonlinear finite element methods. These modeling techniques were benchmarked against numerous historical laboratory tests and live load field tests of in-service PBFTG bridges. Then, the analytical tools were employed in sensitivity and parametric studies on PBFTG bridge models, resulting in proposed simplified empirical LLDFs, which better predict live load distribution than those equations present in the AASHTO LRFD BDS. These tools were also used to assess the effect of bearing line skew on the capacity of PBFTGs. Finally, life cycle laboratory fatigue testing was performed on two PBFTGs joined by a full-scale link slab to assess the applicability of the joint in continuous PBFTG bridges. Results of this project demonstrate the use of PBFTGs can be expanded into continuous spans using link slabs and more accurate LLDFs may