Applications of Field Testing to Bridge Evaluation

Bridge testing is rapidly becoming a major tool in evaluation. Despite improved structural analysis there are numerous cases in which field testing may be the best way to help ensure future safe performance. The reasons for testing include uncertainties in material and structural modeling and concerns for serviceability limit states. Switzerland has long experience in testing new bridges before allowing them to go into service. The general testing plan, the responses that are modeled, and an example are described. The aim in this paper is to extend these bridge-testing methods to strength-evaluation activity. The Swiss approach in testing offers a compromise between a diagnostic performance test and a proof-loading check on capacity. The level of test loading is normally about 80-85% of the code-specified serviceability or unfactored load, which is still significantly above the expected lifetime maximum traffic loading. The paper describes in detail a risk model appropriate to modeling the risks during the testing as well as the benefits in higher safety indices gained after the testing. An example is described in the paper.