Proof load testing of reinforced concrete bridges: Experience from a program of testing in the Netherlands

For existing bridges with large uncertainties, analytical methods have limitations. Therefore, to reduce these uncertainties, field testing of a bridge can be used. A type of such a field test is a proof load test, in which a load equivalent to the factored live load is applied. If the bridge can carry this load without signs of distress, the proof load test is successful, and it has been shown experimentally that the bridge fulfils the code requirements. It should be understood that this method for assessment is different from the diagnostic load tests that are carried out in Ecuador prior to opening a bridge. The loads used for proof load tests are significantly larger. Therefore, it is important to instrument the bridge for a proof load test, and to evaluate during the test that the load does not result in permanent damage to the bridge. To research this topic, and to develop recommendations for proof load tests, a series of proof load tests and a collapse test were carried out in the Netherlands. Additional laboratory testing was carried out as well. Based on this information, recommendations for proof load tests of reinforced concrete slab bridges have been developed for the failure modes of flexure and shear. In the German and North American guidelines for load testing, load testing for shear is not permitted. However, many existing bridges do not fulfil the requirements for shear upon assessment according to the current live load models. Even though more experimental research is needed to develop proof load testing for shear in a guideline or code for the Netherlands, the currently available research results already lead to interesting conclusions with regard to the behaviour of bridges proof load tested in shear, and the required safety margin to avoid damage to the bridge.