Evaluation and Rating of Masonry Arch Bridges

Historic masonry arch bridges were not designed to perform under the load levels typical of modern vehicles. Most of them still perform well due to their inherent strength; others experience various forms of distress. Load rating is the standard approach to assess the capacity of these structures; however, predicting the capacity of an arch bridge is difficult because of the complex behavior of the structure. Mathematical models are powerful tools to predict the actual performance of the structure, but they rely heavily on the accuracy of information provided by field investigations and engineering assumptions. Preservation and rehabilitation of these structures depend on both the success of in situ experimental investigations and numerical analysis. In this paper, a pragmatic approach to assess historic masonry arch bridges is described. The use of nondestructive evaluation (NDE) techniques to assess the existing condition of the structure is briefly discussed. The paper focuses on the load rating procedure provided by the AASHTO Manual for Bridge Evaluation (MBE) (AASHTO 2011). This method is reviewed based on results from a Finite Element Analysis (FEA) and diagnostic load test of a two-span masonry arch bridge over the Pascoag River in Burrillville, Rhode Island. The influence of the analysis assumptions on the bridge rating is evaluated with the aim of providing recommendations on how to improve the accuracy of the AASHTO load rating procedure for masonry arch bridges.