Bridge Girder Buckling during Construction in Edmonton, AB 2

[BAretired]

This was the headline story in the Edmonton Journal this morning. Looks like inadequate lateral bracing but I guess we'll find out in time.

http://www.edmontonjournal.com/coul...ge+girders+found+engineer/10893892/story.html

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[Duwe6]

try "It was noted on Monday morning that the girders were buckled". It would've been a fairly quiet event, and wouldn't have raised a dust cloud. And most 'civilians' wouldn't have noticed the discrepancy.

 

[ajk1]

If there is only horizontal bracing that is not connected to any sturdy support at the ends of the horizontal bracing lines, and no "X" bracing (top to bottom of at least 2 adjacent girders) between the girders anywhere along the length of the horizontal bracing line, is it really braced at all? If all the girders buckle in the same direction, then the horizontal members are not really bracing the girder.

 

[Duwe6]

Lack of adequate bracing. The current plate-girder designs are flimsy & delicate, just like bar joists. Makes them VERY hard to ship from the fab shop to site. They are nice and stiff AFTER the concrete road deck is poured. Not all that stable with all the 'diaphragm' braces are bolted in, but w/o the road deck. LRFD at its 'best'; tall, thin, and wobbly until the last element - concrete deck - is installed. Not a hundredweight of extra steel.

 

[Mekanikles]

Could the thermal movement really have that much of an impact in this case? It doesn't look restraint.

"If you're not part of the solution, you're part of the problem" - John McClane,Die hard

 

[MJB315]

Looks like LTB to me.

"We shape our buildings, thereafter they shape us." -WSC

 

[DamsInc]

try "It was noted on Monday morning that the girders were buckled". It would've been a fairly quiet event, and wouldn't have raised a dust cloud. And most 'civilians' wouldn't have noticed the discrepancy.

That's not what happened. From the articles posted:

"Crews were working on the girders Monday morning when some of them buckled without warning, he said.
"All of a sudden four of them bent simultaneously."

and "It was around 2:15 a.m. Monday and crews were installing the sixth of seven girders at the 102nd Avenue Bridge when the steel beams spanning across Groat Road began to bend before their eyes. "

The first article has a pretty neat before/after shot. Click on the photos tab at the top.

 

[LittleInch]

Interesting photos. It really was 2.15 AM, I thought that was a misprint.

Is it me or in the photo before it bends when its all straight is the crane holding up the nearest spar not vertical? It wouldn't take much to induce a bit of twist in the girder and then when it relaxes a bit feeds into a bend which may not have been seen and then bang. If they were installing them one after the other and constantly moving position it wouldn't take much to get the lift non vertical and induce an ever so slight sideways force.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BAretired]

A 1200 Tonne crane has been installed and is starting to take some of the weight of the buckled girders. The steel is expected to bounce back to nearly straight but an evaluation will be made to see whether the girders need to be replaced or re-used. Should know more by tonight.

I'm betting the girders will not have to be replaced.

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[BAretired]

The following is by Mayes, Edmonton Journal cartoonist:

http://i.embed.ly/1/display/resize?...m/8748/16698633700_8dfc18cbeb_z.jpg&width=810

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[3DDave]

"It was around 2:15 a.m. Monday and crews were installing the sixth of seven girders at the 102nd Avenue Bridge when the steel beams spanning across Groat Road began to bend before their eyes. "

Those beams would have done their bending behind the crew's backs as well. I guess a watched beam still bends.

The real question - did the engineering firm do a stability analysis for each piece as it was placed to see that the constraints were sufficient or did the construction firm blow off required reinforcement as too time consuming? Or both?

In a former life it was often a question for me about the analysis of imperfect parts for stress concentrations, deviations to load paths, assembly loads, and the like. Stress analysis seemed to always be centered on nominal parts with no consideration for variations and a lot of reliance on safety factors.

 

[gwynn]

In reference to a few of the comments above, just to give my insight:

Thermal loads causing the buckling are unlikely IMO. Standard practice in Alberta is that the contractor is not allowed to pour the grout pad beneath the bearings prior to all of the steel being erected and free spanning. In that case the bearings would be resting on steel pintles and the only restraint would be through friction. As noted in the news articles, the girders were fine at 2:10am and buckled by 2:15am. First guess is one girder went as the tension was being let out of the crane lines and the others followed.

The "lean on bracing" installed does not look to be erection bracing. It is likely the top and bottom chord of the permanent diaphragms. As others have noted, it is common to only install the bare minimum amount of bracing required to provide adequate bracing to the girders for supporting their own self weight during erection. Once the girders are up the rest of the permanent diaphragms are installed.

It's close to a 99% probability that there was engineering done for the erection of the girders. This was not a small contractor and regulations in Alberta are strict. If Alberta Transport is responsible for the bridge, they would not allow erection of any of the steel without sealed erection plans that include everything up to how the load is to be relieved on the shoring towers after all of the steel is erected. If it is City of Edmonton responsibility, the requirements may be a bit less.

 

[gwynn]

An edit to the above:

In regards to the bearings, it is possible this bridge was designed with integral abutments, in which case the girders would have likely been bearing on elastomeric bearing pads with no longitudinal restraint.

 

[jayrod12]

I was talking with someone yesterday with some insider knowledge and it appears as though temporary shoring was provided near the splice locations to aid in construction. This shoring was apparently constructed on frozen soil and the warm weather that day (something like 10[sup]o[/sup]C) caused the shoring to settle putting the top chord of those girders in significantly more compression than designed.

This is all of course just an assumption at this point however it seems reasonable.

 

[Guest102023]

Maple syruping season in the Great White North means warm days and sub-zero nights.
I can only see this being caused by buckling caused by temperature effects, but what we can't guess is what was done to leave the structure vulnerable.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[Lomarandil]

Unfortunately vague follow up:

http://edmonton.ctvnews.ca/investigation-finds-cause-behind-bridge-construction-setback-1.2478985

On Monday, officials said a mistake made by the subcontractor hired to install the girders led to the twisted metal.

“The investigation indicated the buckling was a result of the subcontractor responsible for installing the girders misinterpreting the precise bracing details and requirements required,” Barry Belcourt with the City of Edmonton said.

At the time, there were concerns that high winds played a role in the incident – Belcourt confirmed the wind was not a factor.

Belcourt said the subcontractor, Supreme Steel, fabricated the girders and designed the plan on how to install them – but the plan wasn’t followed.