Some reports stated a "stress" test was being conducted on the structure when it failed. Perhaps that was post-tensioning? One has to wonder the wisdom of conducting such as test on the structure over live traffic. Did work on a project that involved post-tensioning, but it was a segmental design, with all segments in place between piers. Likely some BSCE's here can more accurately comment, did take determinate and indeterminate structural design, but did not finish the degree, and found indeterminate to be a bear.