Before workers began adjusting support cables at the north end of the Florida International University (FIU) bridge that collapsed and killed six people last week, they performed the same work at the opposite end of the bridge, the National Transportation Safety Board (NTSB) said in a statement Wednesday.
Adjusting the cables has come under scrutiny as investigators try to explain why the 950-ton span fell suddenly, just five days after it was lifted into place over Southwest Eighth Street near the campus.
Workers had begun adjusting the tension in two rods threaded through diagonal bridge trusses on the north side just before the collapse. The crew was beginning work on the second rod when the 174-ft-long span abruptly dropped.
The work may have been related to cracks in the span’s concrete, reported just two days before the collapse by the project’s lead technical engineer. While he said repairs would need to be made, he did not consider them to be a safety concern. The reason for the road remaining open during the work is part of the investigation.
Engineers not working on the project have speculated that the cracks may have led to adjusting the post-tensioning cables, which strengthen the concrete against the stress of being pulled, and caused the failure.
As part of its investigation, the NTSB is focusing on the span’s north end and is working to remove sections of the span’s floor, the canopy and at least one truss that includes vertical and diagonal members. Investigators also took more core samples from the concrete, adding to earlier samples collected.
Source: Miami Herald