My explanation for the failure of the bridge beams in Edmonton is supported by “new” information. (Ref. 1)
I said in late March that the beams buckled sideways because the cables from the booms of the construction cranes – moving a little in the wind, tugged on the top of the beam pulling it sideways. The bracing was inadequate and could not resist this tugging. (Refs 2 and 3)
(A wind and gust forecast for the site would be useful data. A site specific forecast meteorologist could give this)
My reasoning was based on what I saw in pictures on the Internet of the bridge failure. It was an example of how an idea can be given for the cause of something based on limited information. How a hypothesis – an explanation, for an engineering failure can be based on limited data, a picture in this case, and revised or supported with new data.
This is the process followed in forensic engineering investigation: Hypothesize, investigate, revise. Hypothesize, investigate, revise. Etc. This process was reflected in remarks by another engineer, Yasser Korany, P.Eng., Ontario during a CBC interview. (Ref. 4)
My “new’ data is the manner in which a steel bridge beam supports itself initially and the bridge deck later. The data is not really “new” because bridge beams have always supported themselves in this way. The significance of this dawned on me when I discussed the bridge failure again with a structural engineer in Halifax.
In supporting itself, the steel beam compresses at the top a tiny bit – squeezes together, and pulls apart at the bottom. In the process, the steel beam gets a tiny bit shorter at the top and a tiny bit longer at the bottom.
The shortened beam tries to spring back to its original length – that’s what steel beams do. It tries to do this the easy way by moving sideways.
If something is also tugging the top of the beam sideways, for example, the cable from the boom of a construction crane, then the beam just might do that – move sideways and buckle. The beam trying to spring back to its original length and the crane cable tugging on the beam aid and abet one another in causing the beam to do this.
The buckled beams in the pictures on the Internet do look a little like the curved sections of a water-filled balloon that has been squeezed.
References
- http://news.nationalpost.com/news/canada/traffic-headache-major-edmonton-arterial-road-closed-indefinitely-after-girder-collapse-during-bridge-expansion
- http://www.ericjorden.com/blog/2015/03/27/wind-construction-crane-and-inadequate-cross-bracing-caused-edmonton-bridge-failure-an-initial-hypothesis/
- http://www.ericjorden.com/blog/2015/04/03/why-in-a-recent-blog-didnt-i-seem-to-consider-foundation-failure-as-a-possible-cause-of-the-edmonton-bridge-failure/
- http://www.cbc.ca/1.2999331