Live Load Distribution Factors for Moment in NEXT Beam Bridges

Abstract

In recent years, northeast extreme tee (NEXT) beam bridges have gained increased attention in the bridge industry for their ease of construction. When designing a NEXT beam bridge, the actual live load moment in a beam stem can exceed the design stem moment (i.e., half of the design beam moment) because of the uneven stem spacing. Current guidelines conservatively use the average stem spacing to compute the live load distribution factor (LLDFs) per lane for moment for each stem, which is doubled to calculate the LLDFs for the entire NEXT beam. In this regard, this study aimed to evaluate the applicability of the current LRFD method for LLDFs per lane for moment to the NEXT beam bridges by employing validated finite-element (FE) simulations. Parametric studies were carried out by both simplified and detailed FE modeling of various bridges with minimum- and maximum-width NEXT beams to compute the FE LLDFs. By using the beam spacing and the properties of an entire NEXT beam section, the LRFD LLDFs for NEXT beam bridges were computed as LRFD types i, k, and h sections. The results of FE and LRFD LLDFs were compared, and results showed that LRFD LLDFs governed the FE LLDFs by at least 12%. In addition, it was observed that the LRFD types i and k sections were more applicable for NEXT beam bridges compared with the LRFD type h section.