Modal Test on an Existing Concrete Bridge: Experience Acquired

Modal tests are useful to study the structural health of an existing bridge. However, conducting a test on 'on existing bridge with heavy traffic conditions in a city such as Hong Kong is difficult and rare. This paper presents results from a modal test carried out on an existing prestressed concrete bridge. The results from the modal test were then used to update an analytical model for the bridge. The analytical model was constructed from a beam model with the best mas$ model investigated. Besides the modal parameters, the dynamic elastic modulus and creep factor of the test brIdge were also determined from the modal test. In addition, calibration factors for the bridge deck in the experimental model were obtained from a static system calibration. Bridges in Hong Kong are designed to BS5400 with certain parts replaced by the Structures Design Manual. Discrepancies of the elastic moduli between the experimental and Structures Design Manual values were 27.54% and 12.62% for the static and dynamic moduli respectively. When comparing with the values specified in BS5400, the corresponding differences were only 2.0% and 1.04%. It was shown that when the elastic modulus specified in BS5400 was consistently used, the experimental and the codes specified creep factors would have a difference of 4.53%