The Michigan Department of Transportation (MDOT) on Dec. 28 released the findings of an independent investigation into matters that led the department to halt work on the I-75 Zilwaukee Bridge in Saginaw County.
The report was prepared by an independent consultant hired to review the design, construction and course of action taken by MDOT in 2008 during the bearing replacement project. The report was finalized on Dec. 23.
Shortly after work to remove the existing bearings began, the contractor encountered steel reinforcement and post-tensioning tendons that were not anticipated, leading MDOT to a decision to stop work on the project and conduct a complete safety review. The review led to a decision to design and install a retrofit steel bracing system.
"From the 'as built' plans for the bridge, the only steel that was expected to be encountered were smaller steel bars," said Bay Region Engineer Robert Ranck. "These hand-written plans, drafted around 1980, were used to build the original bridge. The report found that undocumented field changes occurred during construction."
The report, drawn through investigation of consultant reports, renders a finding of no-fault for the April 2008 incident.
"Release of this report was delayed due to ongoing research of as-built plans and the thorough analysis conducted in design preparation for the next bearing replacement project MDOT set to release report findings as Z-bridge investigation nears end Page 2 scheduled for 2012," said Ranck. "We did not want to undermine this process by releasing the report before a full investigation was completed."
"MDOT's release of the independent investigation has been expedited to ensure full disclosure and transparency," said State Transportation Director Kirk T. Steudle. "MDOT field personnel stepped in and stopped work immediately in the interest of safety and the structural integrity of the bridge, which resulted in a complete review."
MDOT officials will use recommendations from the report to develop design, construction plans and oversight for future projects. The Zilwaukee bridge is a segmental bridge and one of the most unique structures in the Midwest. All future projects will have segmental expert consultants on-site during the construction process.