Double-Tee Repairs: Three Case Studies

Precast concrete double-tee (DT) beams are used extensively in parking garages due to their relatively ease of construction and low cost. Three case studies will be presented of different projects in which the stems in DT beams were damaged. The processes for evaluating and repairing those stems will be discussed. In the first two case studies, a stem was damaged by impact from vehicular traffic. A full-depth repair of the impacted stem was chosen as the repair method for both case studies, but considerations to ensure a sound repair, such as shoring, preloading, and venting, will be discussed. In addition, the two case studies will be contrasted to identify why one was more successful than the other. In the third case study, investigation and repair of DT stems that were cracking and spalling in a precast yard and during transportation to the project jobsite will be discussed. Field load tests were conducted to confirm the mechanism of the distress as well as develop an appropriate repair strategy. The use of a mild reinforcing bar that did not extend the full length of the beam was concluded to be the culprit: unintended compressive stresses developed near the ends of the mild reinforcement as a result of the prestress eccentricity. The repair strategy to address the cracking concerns will be presented.