Keeping records and schedule: Cyclic load tests on PT beams
The University of Texas at Austin expanded its campus to include facilities for the Dell Medical School. A 10-story Medical Office Building completed in 2016 was part of this expansion. The building includes six levels of parking, professional office space, outpatient clinics, and a surgery center. Upper levels of the concrete frame structure included elevated pan formed beams supported by post-tensioned (PT) concrete beams
During construction, records of post-tensioning were lost. As such, the amount of prestressing force in the PT beams, and thus their ability to resist the design loads, was uncertain.
In the absence of a reliable method to measure the strand stress directly, Pivot performed load tests on four of the beams in question. Pivot used results of a field investigation, nondestructive testing, finite element analyses, and coordination with the Structural Engineer of Record to design the load tests and predict structural response to applied load.
At Pivot's recommendation the University accepted the cyclic load test method described in ACI 437.2. This method allowed Pivot to test each beam within a period of 6 hours as opposed to 24-30 hours required of traditional test methods. As the method is performed with multiple load steps and cycles, Pivot showed the University and the Structural Engineer of Record precise comparisons of beam behavior following the tests. Using sophisticated data acquisition equipment and techniques, Pivot monitored beams in real time and determined the beams passed their respective load tests as soon as the testing wrapped.
Finite Element Analysis
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