Load Rating of a Reinforced Concrete T-Beam Bridge Through Ambient Vibration Testing and Finite Element Model Updating

As the load demands on highway bridges increases, it is essential that the load rating procedures reliably assess the condition of existing structures. In addition, conventional design office load rating techniques cannot be used for bridges without structural plans, which indicates the need for a more advanced load rating procedure. This paper presents a methodology to compute the live load-carrying capacity of reinforced concrete T-beam bridges, which can be applied for bridges with structural plans or with missing or limited design information. The method involves modal identification of bridge using ambient vibrations and finite element model updating using vibration characteristics for capacity estimation. A simply supported T-beam bridge located in Virginia is selected for field-testing to verify the proposed method. The bridge is composed of five spans of the same length, 12.95 m for each, with a total length of 65.4 m and a width of 8.864 m. A total of nine accelerometers are installed to bridge to collect acceleration data for 15 min at a sampling rate of 500 Hz. The modal properties of the bridge are determined using enhanced frequency domain decomposition technique. The initial finite element model of the bridge is updated such that the modal properties of the bridge match the field measured parameters. The load effects and capacity of the bridge are determined and used to calculate the load rating factor. The rating factors obtained from the proposed method and traditional design office load rating procedures are compared. The results indicate that the proposed method can reveal the reserve capacity of bridges.