On Dec. 13, 2000, a motorist was traversing the northbound section of Milwaukee’s Hoan Bridge when he discovered a slump in the pavement on the bridge’s surface. He immediately called 911 to report the obvious defect to the proper authorities.
Opened in 1977, it was designed to carry traffic to and from downtown Milwaukee to the south side of the city. The average daily traffic (ADT) at the time of the reported problem was 36,590.
That telephone call resulted in a series of very rapid and dramatic steps taken by the Wisconsin DOT.
First, the entire bridge, which is composed of two structures, northbound and southbound, was shut down to all vehicular traffic. An inspection was conducted, and it was determined that portions of the northbound section would need to be removed.
Second, Controlled Demolition Inc., Phoenix, Md., on Dec. 28, 2000, imploded the failed section of the northbound structure.
The immediate short-term goal of the DOT was to reopen the Hoan Bridge to two lanes of car traffic as soon as possible, while utilizing safe construction methods to do so.
A number of consultants and universities were involved in accomplishing that goal, including Lichtenstein Consulting Engineers, New York, N.Y., which was retained to conduct an in-depth inspection including the failure analysis.
First, platforms needed to be placed and secured from which inspection procedures could be implemented. Next, all the paint was removed at connection areas down to bare metal in order for the inspections to be made. It was determined that the cracks were occurring at the shelf plates in the webs of the three-girder-system sections of the bridge.
Lichtenstein developed a retrofit procedure, which involved drilling four "mouse holes" at joint locations where stress could create the cracks that had been discovered.
Lichtenstein conducted the in-depth inspection in conjunction with STS Consultants, Milwaukee, who was certified to conduct magnetic particle testing. All "mouse holes," including existing cracks, were documented by pictures and drawings indicating their locations.
Weight problems
Due to the weight and space limitations on Hoan Bridge, it was decided after consultations with Traffic Signing & Marking Co., Madison, Wis., the traffic control contractor for the project, that reboundable, spring-loaded, vertical panels, as manufactured by Impact Recovery Systems Inc. (IRS), San Antonio, would be used to separate traffic upon reopening of the bridge.
Weight issues eliminated the possibility of using a concrete barrier wall. Representatives of the Wisconsin DOT felt that the visibility afforded by tubular markers was not adequate and space requirements would not allow the use of drums, making the IRS product an ideal candidate.
According to Bob Hubing, construction services field engineer for the Wisconsin DOT, it took 50 people and 15 consultants working six days a week to expedite the reopening of the southbound roadway to two-way car traffic. That high profile reopening, televised on all of the Milwaukee television stations and attended by the governor of Wisconsin, the secretary of transportation and the mayor of Milwaukee, occurred on Feb. 17, 2001. Since the goal of reopening the bridge to two-way car traffic was accomplished on that date, the ADT has returned to 24,100.
Lichtenstein continues its evaluation of the cause for the failure and is working to develop their recommendations for the possible reconstruction of the bridge’s northbound section.
Meanwhile, biweekly inspections of the bridge will continue. Tests and lab analysis, future maintenance cost and life-cycle cost analysis all will be considered in determining the long-term fix for the Hoan Bridge.
