Dynamic Characterization of a Prestressed Concrete Bridge by Strain and Acceleration Measurements

Abstract

Structural health monitoring systems for bridges typically employ a mixture of different types of sensors to measure and track long-term structural performance under various environmental and service live loads. A significant challenge in designing such monitoring systems is to optimize the quantities and locations of the different sensor types to achieve the monitoring objectives while minimizing instrumentation costs. The final instrumentation design is usually a compromise between an ideal instrumentation plan and one that incorporates economic and practical considerations and constraints. It follows that there is merit in exploring the use of different types of sensors to accomplish more than one characterization objective. This paper presents a study to explore the limits of using both strain gage and accelerometer measurements from a prestressed concrete highway bridge for the dynamic characterization of the structure. The bridge specimen used for this study is primarily instrumented with strain gages to measure the stresses induced by heavy trucks. A smaller array of six accelerometers is also included specifically to measure characterize the vibration response of the bridge due to different truck loads, configurations and crossing speeds. The accelerometers are installed along the transverse and longitudinal centerlines of the bridge span. Strain gages are installed on each beam in the bridge cross section at 28%, 32% and 50% of the longitudinal span length locations. The monitoring system operates in a triggered acquisition mode in which the strain gages and accelerometers are both sampled at 200 Hz during truck crossing events. Strain and vibration measurements from truck crossing events are individually processed and evaluated to identify the dynamic characteristics, and the combination of the two types of measurements for dynamic characterization are evaluated and discussed.