Laser-Based Instrumentation for Bridge Load Testing

This paper describes the developments and application of a laser-based instrument used to experimentally load test bridges. The instrument is used to quickly and unobtrusively measure bridge girder deflections under static loading. The system can be set up in the median or shoulder of the roadway under the bridge without altering traffic. Data can be collected on multiple girders from one measurement location without requiring access to the girders, and no special targets are required on the girders. As a result, this type of a system can greatly speedup the process of load testing a bridge. In fact, the system can allow bridges to be load tested that would be difficult or impossible under other circumstances. To help understand the way the instrument is used, a description of the basic system operation is given followed by a detailed explanation of the main instrument features. Details of the procedure used to measure vertical deflection of bridge girders are discussed. Finally, an overview of the experimental local tests performed with the NDEVC laser system is presented.