The United Services Automobile Association (USAA) in San Antonio, Texas, was renovating and adding new batteries on one of its battery back-up rooms, requiring additional load capacity for the floor.  VSL was engaged by JD Hunt Construction to design an external post-tensioning system to be installed below the room floor.

The area involved was approximately 150 feet by 250 feet. Installation was performed in confined space beneath the floor, utilizing fans for air circulation and oxygen monitors to ensure safety of the crews.

VSL cored through two forty inch wide beams using extensions on the core rig. Deviators were bolted to the bottom of joists and welded together using a flat plate. Ducts were then installed through the holes in the beams (six ducts, in total), and unbonded monostrands were pulled through using a centralizer to keep the strand centered in the ducts as they were grouted. Although it is unusual to utilize monostrand in grouted ducts, VSL proposed this alternate solution to the galvanized strand initially shown in the plans to improve durability and fire resistance. Using the centralizer ensured the strands would stay centered in the duct during grouting, providing the additional fire resistance.

Stressing was performed in two stages in order to avoid overstressing the joists.  The Engineer required half of the new batteries to be placed before the initial stressing operation.  After half of the batteries were placed, the top four strands were stressed. Then, the remaining batteries were placed and the balance of the strands stressed.