Live Load Distribution Factors for Steel Press-Brake-Formed Tub Girder Bridges

Abstract

Accelerated bridge construction (ABC) has been widely used in the United States since the late 1990s following a national ABC initiative by the Transportation Research Board (TRB) in 1996. The press-brake-formed tub girder (PBFTG) system is one of the innovative bridge systems that has been developed recently for the accelerated construction of simple and short span bridges. The PBFTG shape is optimized to achieve the maximum structural capacity and torsional stiffness due to the distribution of the steel around the centroid of the shape, a major limitation in conventional W-shape and plate I-girders. Despite the promising advantages of PBFTG systems, it received less attention than conventional superstructure systems, especially when dealing with their live load distribution factors (LLDFs). Stemmed from these limitations, LLDFs for moment and shear of one and multiple design-loaded lanes for exterior and interior beams in PBFTG bridges are computationally investigated. More than 190 bridges are modeled using a validated finite-element (FE) approach to cover a wide range of geometric parameters of PBFTG bridges, including spacing between beams (S), bridge span (L), skew angle (θ), and number of lanes (NL). Detailed FE models show that LLDFs of PBFTG bridges are highly dependent on the selected geometric parameters. A regression analysis is performed leading to a new proposed set of equations for studies showing that the LLDFs of PBFTG bridges are highly dependent on the selected geometric different types of LLDFs for fascia and interior beams in PBFTG bridges. The results of the parametric study suggest that the current AASHTO equations are unconservative for both single lane and multilane moment and shear LLDFs for fascia and interior PBFTGs compared with proposed equations (except for single lane moment LLDFs of interior beams).