The SH-75 SB Bridge over McKinney, Texas was observed to have excessive vibration, cracking and the pothole on the concrete deck. It was very unusual to have such vibration for a newly built (built-in 2011) prestressed concrete girder bridge. The objective of the research was: (1) to evaluate the vibration problem using a combined Non-Destructive Evaluation (NDE) and diagnostic load test, ambient vibration test and dynamic load test; and then (2) to propose a proper retrofitting method using a calibrated Finite Element Model.

A diagnostic load test combined with NDE (Ground Penetrating Radar and Impact Echo) confirmed a loss of composite action between the superstructure elements and delaminations of the concrete deck. To evaluate the rate of deterioration, a follow-up load test was conducted after a year which demonstrated identical results. An ambient vibration test under regular traffic was conducted on the SB Bridge as well as on two other bridges with similar geometry and girder properties but no significant vibration problem for comparison. A dynamic load test was also conducted on the SB Bridge to calculate the mode shapes and natural frequency.

After the testing phase was completed, the SB Bridge was modelled in a Finite Element Software Package (ABAQUS CAE) and then calibrated based on the experimental load test and vibration test results. Finally, feasible retrofitting methods was studied on the calibrated model and the most effective one will be suggested to the bridge area office to improve the serviceability and durability of the bridge.

IE system was used to determine the delamination condition and thickness of concrete structural members when voids, honeycombs, and/or cracks are suspected. The device created an impact at a spot on the surface, and then recorded and analyzed the echo.

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