Comparison of slab-bridge safety assessment strategies

When assessing the safety of existing structures it is often not economic to use the design codes, which may be rather conservative in nature. In this paper, safety is measured in terms of the factor of safety, defined as the ratio of available strength to total load effect. The paper examines the sensitivity of the safety factor of two example concrete slab bridges to: (1) the method of structural analysis and failure criterion; (2) the inclusion of updated strength information; and (3) the application of site-specific loading. It is shown that in certain cases plastic analysis methods can predict the ultimate load capacity more accurately than conventional elastic analysis. Methods are suggested for calculating the material strength values based on test results so as to better reflect the true in situ strength of the bridge. Finally, the use of a bridge-specific load model is suggested which may lead to an increase of the factor of safety.