Load rating of tied-arch bridge systems

Abstract

The National Bridge Inspection Standards require highway departments to inspect, evaluate, and determine load ratings for structures defined as bridges located on all public roads. Load rating of bridges is performed to determine the live load that structures can safely carry at a given structural condition. Bridges are rated for three types of loads, design loads, legal loads, and permit loads, which is a laborious and time-consuming task as it requires the analysis of the structure under different load cases. Several tools are currently available to assist bridge engineers to perform bridge rating in a consistent and timely manner. However, these tools support the rating of conventional bridge systems, such as slab, I-girder, box girder and truss bridges. Recently, several innovative bridge systems have been developed, such as tied-arch bridge systems used in the construction of Ravenna and Columbus bridges in the state of Nebraska, USA. The objective of this paper is to present the procedures and models developed for the load rating of tied-arch bridges. This includes developing analytical models and performing rating factor calculations in accordance to AASHTO Load and Resistance Factored Rating specifications. Three-dimensional finite element models were developed and rating calculations were performed for the primary structural components assuming various percentages of section loss and using the most common legal and permit loads in addition to AASHTO live loads. Analysis and rating were also conducted for an extreme event where one of the hangers is fully damaged.