Bridge Collapse

[tw]

Originally Posted by xoxoxoBruce

They have finished with the bird shit and are moving to the deicing system next.

I am still waiting for analysis that includes significant terms such as 'fatigue'. Also troubling is that redundancy did not exist on this bridge. Redundancy is even found in Roebling 1880 bridge - the Brooklyn Bridge.

Rusting is a common problem in so many bridges such as NY's Williamsburg Bridge that was not painted for 30 years. It took a falling structural member to finally get maintenance restarted.

One need only visit Philadelphia to view Interstate 95 some 40 feet above those neighborhoods. Rust is rampant everywhere. Is that 6 or 8 lanes highway ready for collapse?

The Golden Gate Bridge gets repainted constantly. A painting crew is constantly repainting that bridge. With landfall on Marin County, then the painting starts all over again in San Francisco. How many other bridges get that kind of maintenance?

But rust alone typically does not cause fatigue; would be unacceptable long before rust could create fatigue. However this MN bridge had no redundancy. This then begs the question why routine electronic monitoring is not installed on bridges without redundancy.

Questions that we should expect an engineering analysis to answer.

[xoxoxoBruce]

Originally Posted by tw

One need only visit Philadelphia to view Interstate 95 some 40 feet above those neighborhoods. Rust is rampant everywhere. Is that 6 or 8 lanes highway ready for collapse?

I've been hearing "experts" grumbling, for several years, that the whole elevated section of I-95 through Philly should be completely rebuilt. What a clusterfuck that would be.

[tw]

Originally Posted by xoxoxoBruce

I've been hearing "experts" grumbling, for several years, that the whole elevated section of I-95 through Philly should be completely rebuilt.

A point made (if I remember) in The Economist. There is no political reward for doing maintenance. Political reward is in building something new. Mayor Lindsay in NY had two choices. Maintain the bridges (ie Williamsburg) or rebuild Yankee Stadium - corporate welfare for the Yankees. Lindsay rebuilt Yankee Stadium.

Don't paint I-95 and don't do any maintenance on Veteran's Stadium - and the city will get everyone in PA to rebuild them. Phillies were given a new stadium for free paid for by all PA taxpayers. Clearly that was cheaper than standard maintenance.

[xoxoxoBruce]

Monday morning quarterbacking on the net.

At http://taxa.epi.umn.edu/bridge/ an Epidemiologist (it's about diseases, nothing to do with bridges or engineering) weighs in with his theory.

He's blaming the construction/repair work.... with 8 x 10 glossies and a paragraph on the back.

[warch]

Trying to share some pics of one of the sorting sites. Lots of scrap has gone through the site- metal, rebar and concrete. Barges bring it down, it is sorted and categorized then barged or trucked to another place for study.

not sure how to post a pic. If youre interested. you can send me a message and give me some posting tips...I give up!

[glatt]

Originally Posted by tw

Questions that we should expect an engineering analysis to answer.

A story in this morning's paper contains information leaked by someone on the investigation. Apparently it was a design flaw, not rust or poor maintenance, that caused the failure of the Minnesota bridge. The gusset plates were not thick enough.

The National Transportation Safety Board is expected to announce today that investigators have traced the failure to steel structures known as gusset plates that held together beams on the Minneapolis bridge, according to sources who spoke on condition of anonymity because they were not authorized to discuss the board's findings.

Some gusset plates on the bridge, which carried eight-lane Interstate 35W across the Mississippi River, snapped during evening rush hour on Aug. 1, leading the bridge to crumple, according to the sources.

Gusset plates are common on steel bridges across the nation, including in the Washington area. They hold together angled beams on the bridge's frame.

The sources said the fault in the Minneapolis span stemmed from the bridge's design and would not have been discovered during detailed state inspections.

When the bridge was built in the 1960s, its gusset plates were not thick nor strong enough to meet safety margins of the era, the sources said. Over decades, renovations added weight to the span. It was undergoing a construction project with heavy equipment and material at the time of the collapse.

The sources said investigators were not sure what role those projects played in the incident. But investigators have speculated that the weight from equipment and materials may have triggered the plates' failure, two of the sources said.

During the construction projects, the sources said, state officials and contractors did not recalculate how extra weight might affect the gusset plates. They said it was not standard procedure to do such studies.

The NTSB has not uncovered similar flaws in other bridges, the sources said.

The safety board is expected to recommend at a news conference today that federal and state authorities conduct more rigorous engineering studies of gusset plates before beginning renovation projects on bridges in the future, the sources said.

[tw]

The first gusset plates suspected to have failed was U10. But which one is U10? Graphics observed so far say nothing.

The cascading failure resulted in failure of (was it?) 6 (or 8?) other plates. Still under study is why this plate failed at this time. What was the unique event that finally triggered the failure?

Gusset plates were one half the required thickness. Plates should be thicker (stronger) than connecting beams. Were they literally same or lesser thickness than the beams? In which case, why was this weakness not physically obvious to experienced construction workers?

[xoxoxoBruce]

Years of making the bridge heavier, then piling on a bunch of construction equipment plus rush hour traffic, eventually became the straw that broke the camel's back.