Development of Live Load Distribution Factor Equation for Concrete Multicell Box-Girder Bridges under Vehicle Loading

Won Choi,Junsuk Kang,Jongsup Park,Iman Mohseni

doi:10.1186/s40069-019-0336-1

Abstract

The evaluation and design of concrete bridges in large part depend on the transverse distribution characteristics of the live load carried and the service level. The live load distribution for continuous concrete multicell box-girder bridges varies according to bridge configuration, so when designing such bridges, it is important to determine the maximum negative stress at the piers, the midspan positive (tensile) stress and the deflection of the bridge when subjected to live loads. This paper reports an extensive parametric study to determine the maximum stress, deflection, and moment distribution factors for two span multicell box-girder bridges based on a finite element analysis of 120 representative numerical model bridges. Bridge parameters were selected to extend the parameters and ranges of current live load distribution factors defined by AASHTO LRFD specifications. The results indicate that the span length, number of boxes, and the number of lanes all significantly affect the positive (tensile) and the negative (compression) stress distribution factors. A set of equations proposed to describe the behavior of such bridges under AASHTO LRFD live loads yielded results that agreed closely with the numerically derived results for the stress and deflection distribution factors.

Highlights

Concrete multicell box-girder (MCB) bridges are commonly used for highway bridges in road networks all over the world
The load distribution factor (LDF) formulae presented in the latest edition of the AASHTO LRFD Bridge Design Specifications (2017) are based on extensive numerical and field tests performed on bridges with various geometries (Zokaie et al 1993), but their accuracy has not been reevaluated in the light of recent research in this area
As previous sensitivity studies revealed that changing the slab thickness has an insignificant effect on the live load distribution factors (Huo et al 2003; Huo and Zhang 2008), only the following parameters were investigated in this study: the span length, the number of lanes and the number of boxes

Summary

Introduction

Concrete multicell box-girder (MCB) bridges are commonly used for highway bridges in road networks all over the world. The LDF formulae presented in the latest edition of the AASHTO LRFD Bridge Design Specifications (2017) are based on extensive numerical and field tests performed on bridges with various geometries (Zokaie et al 1993), but their accuracy has not been reevaluated in the light of recent research in this area. These specifications do not provide sufficient details to justify and confirm the accuracy of the modification factor for continuity that has been proposed (Samaan 2004; Barr et al 2001; Higgins et al 2011; Hughs and Idriss 2006).

Objectives

Findings

Discussion

Conclusion