Dynamic Load Allowance Provisions for Box Culverts with Low Fill Depth

Abstract

It is well established that vehicular traffic traveling over bridge-like structures can impart a dynamic load effect that is greater than vehicles’ static weight alone. In order to account for this increased load, bridge design codes use a factor known as the dynamic load allowance (IM) to amplify static vehicular live loads. In the current version of the American Association of State Highway and Transportation Officials (AASHTO) Manual for Bridge Evaluation (MBE), reductions in IM are allowed for bridges having span lengths greater than 12.2 m with road surfaces in good condition. In addition, the current AASHTO LRFD Bridge Design Specifications allow for a reduced IM for culverts with higher fill depth. However, many culverts have neither span lengths greater than 12.2 m nor higher fill depths and thus are not eligible for such IM reductions. This paper investigated whether similar IM reductions can be considered for culverts with smaller span lengths and fill depths. The field experiments conducted suggest that culverts having span lengths less than 12.2 m and fill depths less than 0.5 m could be considered for similar IM reductions allowed by the MBE.