Abstract

     Of the 604,485 bridges in the United States, approximately 21% are culverts having a span of 6 m (20 ft) or greater. The load rating of typical bridges presents numerous challenges. Developing load ratings for non-typical structures, such as buried arch-shaped culverts is more complex because of the culverts’ unique geometric configuration and their interaction with soil media. This paper proposes an alternative analytical method for load rating in-service reinforced concrete (RC) arch culverts that overcomes the limitations of the widely used elastic frame concept while being straightforward to implement. The proposed analytical method uses two-dimensional finite element models of the arch structure and surrounding soil media. The finite element model was first validated against experimental tests on a full-scale RC arch culvert, subjected to simulated live loads. The validated FE model was used in load rating analysis of 21 RC arch culverts with large fills. It was found that for arch culverts with fills exceeding 2.43 m (8 ft.), the controlling actions are bending moments at the crown and haunch. For culverts with fills greater than 3.05 m (10 ft.), live load effects become negligible. A revised rating formula is proposed for culverts with this characteristic.

Introduction

     Bridge collapses in the United States (US) resulting in human loses and property damages (e.g. the I-35W Mississippi River bridge in 2007) have prompted executive and legislative authorities to enact more stringent measures to ensure that in-service bridges operate safely and reliably. As part of these efforts several bridge inspection and maintenance guides have been published, such as the National Bridge Inspection Standards (NBIS), the Federal Highway Administration’s (FHWA) Bridge Inspector’s Training Manual 70 (Manual 70), the American Association of State Highway Officials’ (AASHO) Manual for Maintenance Inspection of Bridges, and the Culvert Inspection Manual [Bridge Inspector’s Reference Manual, BIRM (2012)]. These guides provide valuable instructions on when and how to inspect and evaluate bridge structures. For example, NBIS requires load ratings for all highway bridges located on public roads; if the rating is insufficient, it should be posted, for all legal loads and un-restricted routine permit loads (NBIS 2014).

     As the population has grown over the past 50 years, traffic volumes and truck weights have increased in order to deliver more goods and services. At the same time, aging, environmental exposure, and other natural events deteriorate infrastructure. The combined effects of higher traffic volumes and infrastructure deterioration make the structural evaluation of bridges and culverts of paramount importance. However, the load rating of typical bridges is not simple, and that of non-typical structures, such as buried archshaped culverts, is even more complex because of their unique geometric configurations and their interactions with soil media (Seo, Wood, Javid, & Lawson, 2017; Wood, Lawson, Surles, Jayawickrama, & Seo, 2016; Wood et al., 2017).

Conclusions

     This study investigated the load rating of bridge-size RC arch culverts. It proposes an alternative analysis method that overcomes the limitations of the widely followed elastic frame concept. The method uses 2-D FE models that automatically and accurately calculate gravity loads for all parts and includes the soil’s passive pressure as result of discrete modeling of soil media in the vicinity of the arch. Furthermore, the proposed FE models include a method to accurately represent truck loads on the culverts. This is achieved by generating the entire truck (with respective axle weights and spaces) and moving it across the length of the model to determine maximum forces within the arch culvert. Several types of trucks (e.g. single, tandem, or multiple axles) can be input into the model. It can also handle the presence of several trucks.