CIVIL ENGINEERING 365 ALL ABOUT CIVIL ENGINEERING



AbstractVibration of highway bridges, although often ignored, is a serviceability issue that may contribute to concrete deck cracking and delamination. A recently constructed prestressed concrete bridge in the Dallas–Fort metroplex experienced extensive transverse deck cracks, potholes, and excessive vibration. The bridge was load-rated employing a novel and combined Nondestructive Evaluation (NDE) and load test method. Ground Penetrating Radar scans showed satisfactory concrete cover for the top reinforcement in the deck, indicating negligible surface wearing and construction error. Impact Echo scans of the top of the deck revealed severe concrete delamination at the top of the girders with fully cast-in-place (CIP) concrete and also at the interface of the precast deck panels and the CIP topping. The calculated neutral axis depths of the composite girders using an initial and follow-up load test after about a year were found to be in the web, indicating only 59% partially composite action. It was concluded that the excessive vibration was due to the deck delamination and the partial-composite action that reduced the stiffness of the superstructure. Both the deck and the composite girders can safely carry HS-20 live loading as required by the Texas Department of Transportation. However, the long-term bridge serviceability and durability could be compromised due to the concrete degradation and loss of stiffness.



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