Aileen Cho

Aileen Cho Engineers discussed the collapse’s implications for the industry.

Highly technical sessions on topics like bridge aesthetics, seismic tests and cable analysis dominated the fourth annual New York City Bridge Conference on the first day, Aug. 2. But a special evening session on bridge collapses, spurred by the Aug. 1 collapse of the Interstate 35W bridge in Minneapolis, brought out a deeper sense of self-reflection and questions about the state of the industry.

In response to the tragedy, Khaled Mahmoud, president of Bridge Technology Consulting, New York City, and chairman of the Bridge Engineering Association, organized the evening forum on types of bridge failures. Experts discussed the history of bridge failures due to scour, earthquake, cable vibration and brittle fracture. But nobody wanted to speculate on the possible causes of the Minneapolis collapse. In response to an audience member’s query, Mahmoud said, "There are not enough facts at this point. I think it’s way too early to issue judgment." Bojidar Yanev, director of bridge inspection for the New York City Dept. of Transportation, expressing empathy for MinnDOT as a fellow owner, noted that "there has never been just one reason” for previous bridge collapses. He said wryly,"Let’s ‘enjoy’ the suspense by not talking about it."

Another audience member cited political failure, referring to the chronic underfunding of infrastructure. Arun Shirole, director of the National Steel Bridge Alliance, noted that engineers can and should close bridges that they know are unsafe, regardless of political pressure. Bala Sivakumar, chief engineer with Lichtenstein Consulting Engineers Inc., Paramus, N.J., noted that even 20 years ago, American engineers were not designing for extreme events like earthquakes, terrorism or barge impacts.“But there is not enough money to fix everything,” he added. “There are many missing elements in our process. This [Minneapolis bridge collapse] will make us rethink again.”

Frieder Seible, dean of engineering at the University of California, San Diego, noted that seismic retrofits have always followed lessons learned from each big earthquake. While the 1971 Sylmar quake spurred a $10-billion retrofit program to reinforce California freeway columns against shear failure, little has been done so far to retrofit abutments in the wake of the 1994 Northridge earthquake, he said.

Ties to Security

To an extent, the recent collapse also overshadowed some sessions at the conference, ranging from hardening bridges against terrorist attacks to academic proposals for new bridge-inspection methodology. For instance, Sivakumar said the American Association of State Highway and Transportation Officials might take a new look at standards for evaluating bridge connections. AASHTO’s revised manual on bridge load-rating evaluation standards, due out this fall, currently focuses on updates to timber bridges, and overall fatigue evaluation of steel, segmental and curved-girder bridges, plus considerations of new types of trucks and vehicles.

In another session, Marcus Knight, professor at Middle Tennessee State University, proposed a new scale for inspection of concrete bridge decks to encompass differences between partial-depth deterioration, full-depth deterioration and structural cracks. Mohammed Ettouney, principal with Weidlinger Associates, New York City, said a study is under way on the possibility of combining elements of structural health monitoring of bridges with plans for hardening them against terorrism.“Does it make sense to talk about health monitoring and bridge security in the same sentence?” he asked rhetorically. A published report is pending.

Malcolm Kerley, chief bridge engineer for the Virginia Dept. of Transportation, noted one direct effect of the Minneapolis bridge collapse on VDOT’s antiterrorism efforts: “We restricted individual inspection reports” on critical structures. Although VDOT put information about bridges and their federal ratings on its Website, it will not release structural drawings and plans or exact locations of fracture-critical bridges to the public.