Assessment of bridges: use of dynamic testing: Reply

Abstract

The main thrust of the paper was the assessment, using dynamic response, of effects of repairs on the bridgeis condition. This assessment did not include determining the load-carrying capacity of the bridge. One is aware that assessment engineers would like the ability to determine load capacity. Unfortunately, there is at present (to my knowledge) no quantitative relationship between dynamic response and load capacity. One of the conclusions of the paper was that detailed studies of relationships between dynamic properties and load capacity need to be conducted. The author is of the same conviction that dynamic response of a structure is not directly related to load-carrying capacity. This opinion is expressed in the paper. The abstract specifically says that the procedures described are most useful for monitoring changes in structural condition with time. When using dynamic monitoring for integrity assessment, it is stiffness and not strength that is being assessed. Thus, defects causing loss of strength without reduction in stiffness or changes in mass might not be detected. The proposed definition for structural assessment, in the context of the paper, needs to be broadened to read as follows: evaluation of the structural condition, including the load distribution characteristics, of bridges on the basis of observed and (or) measured dynamic behaviour. It should be noted that results from dynamic testing for structural assessment are usually evaluated relative to previous tests or an analytical model. I think the definition proposed for integrity of a structural system is rather limited. Though the measured response is due to the applied dynamic test loads, characteristics of the response are more general to the state of the structure, since dynamic response is a sensitive indication of the physical integrity of any structure. In the context of the paper, integrity assessment of a structural system is the ability of the structure to remain intact, relative to a benchmark, as characterized by its dynamic properties.