Results of In-Service Monitoring of a Sample of Typical Highway Bridges

The typical biennial bridge inspection is more qualitative than quantitative in nature, and as a result, sufficiency ratings will vary depending on the inspector. It is clear that to better manage our bridges, more quantitative data about the bridge behavior under site specific traffic needs to be gathered as part of the inspection process. A project is currently underway at the University of Delaware Center for Innovative Bridge Engineering (CIBrE) to gather in-service strain data from a sample of twelve typical slab-on-steel girder bridges, in conjunction with the bridge's biennial inspection. The bridges to be monitored have been selected from those in the state that are due for inspection, and where access is relatively easy. On the day of the inspection, a single strain transducer and battery powered monitoring system are installed on a key location on the bridge (typically at mid-span of a girder). Strains are then continuously monitored for a period of two weeks. After that time the data and monitoring system are retrieved. The data recorded includes just peak strain recordings that exceeded a specified threshold, as well as the date and time at which they occur (the quantity of actual data is limited). The collected data is to become part of the permanent inspection record of the bridge. Future records can be compared to the original records to see if there is any difference in the response, which might suggest possible damage or deterioration, or changes in the traffic. The data is also used to estimate a two-year load rating factor for the bridge that should be more reflective of the actual condition of the bridge. Presented in the paper is a description of the sample of twelve bridges that have been monitored. Sample data from two bridges is presented and the updated load rating factors are presented.