Nondestructive Radiographic Evaluation and Repairs to a Prestressed Concrete Parking Structure Following Partial Collapse

Abstract

This paper presents use of radiographic imaging (X-ray) in evaluation of existing reinforcing steel and tendon configuration of a structure following a collapse and development of steel retrofit and carbon-fiber-reinforced polymer (CFRP) repairs. A collapsed section in the driving surface in a precast concrete parking deck prompted an engineering evaluation and survey of the entire deck for assessment and repairs to distressed members. Distress was identified in decking members and perimeter spandrel beams in varying forms and degrees. Repairs to the decking members involved supporting the distressed decking using supplemental steel retrofit brackets installed through the double-Tee stems containing prestressing tendons. The precise location of the tendons in the stems needed to be identified to implement this repair in order not to damage the tendons during drilling for through-stem anchors. Radiographic X-ray imaging in this application enabled locating and avoiding the tendons in the stems to support and strengthen the decking member. The supplemental steel brackets also enabled continued and improved operation of an existing expansion joint in the area of repair. Radiographic evaluation technique was also used in identification of steel reinforcement configuration in the perimeter spandrel beams exhibiting cracking at bearing locations with maximum shear. Radiographic exposures were used for evaluation of existing steel configuration and development of CFRP repairs. CFRP repairs were implemented in perimeter spandrel beams while decking surfaces were retrofitted with steel brackets to support the driving surfaces and enable continued expansion and contraction in the existing expansion joints.