Weather Condition at 9:56 am on morning of May 15 (Denver Airport)
Wind: 3 MPH from the NE
Temperature: 59 Deg. F.
Dew Point: 43 Deg. F.
Humidity: 55%
Sky Conditions: Partly to Mostly Cloudy, Visibility Unlimited
The newspaper sketches indicate that the girder was sitting on the concrete cap. Coefficient of friction for steel on concrete: 0.47, reference ASCE (
unclesyd,
The splice is to connect the sections together. You can only ship about 120' section of girder and this being a continuous bridge, the entire girder is probably 200' or more.
The splice is also a convenient point to change the section for a more economical girder. Most likely to the left is the negative moment region, which has a higher moment, which would require a larger section, thus the heavier flanges.
Thanks for the note on the environmental conditions.
I suspect that the conditions at the site were much different since DIA is out in the plains well east of Denver (say 45 minutes east). Golden Colorado which is where my papers noted this project is at least that much west of Denver and in a completely different terrain.
In fact, Denver is a nice place to get into to some cool computational wind modelling as its terrain defies hard and fast regulations of the codes.
Another point about the bearing. I would believe that the girder bears on more than the concrete beam cap of the intermediate bent. Most applications involve a significant sole plate (1.5" of steel) sitting on a very durable neoprene pad, laminated if necessary. The pad helps the girder to sustain temperature movement by shear deformation and rotations. This rotation capability probably didn't help keep the girder upright at all.
Ckenny,
My heart goes out to your community. This is a very tragic accident.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
Qshake - Thanks for bringing me back to reality about both Colorado geography and the fact that the girder had to be on a bearing plate. Guess "I did not see the forest for the trees."
I have a copy of a poem from Rudyard Kipling on my wall to remind me of my responsibility as a structural engineer:
"Hymn of Breaking Strain"
The careful text-books measure
(Let all who build beware!)
The Load, the shock, the pressure
Material can bear.
So when the buckling girder
Lets down the grinding span,
The blame of loss, or murder,
Is laid upon the Man.
Not the stuff - the Man!
A standard note for Colorado Department of Transportation (CDOT) bridge plans reads "THE CONTRACTOR SHALL BE RESPONSIBLE FOR THE STABILITY OF THE STRUCTURE DURING CONSTRUCTION". I assume it was on the plans for this bridge. Does this relieve the engineer of legal responsibility? How about moral responsibility?
It is common to add stiffeners to the exterior face of the existing exterior girder so that cross frames can be attached when a bridge is widened. Does anyone have any idea why this was not done in this case?
For the case of the existing structural steel I can't imagine welding but certainly they would use bolted angles as a means of providing the necessary connection plates for the crossframes. And why would you not wish to attach the cross frames to the erected girder since this is the fastest pick of several frames at once. Otherwise you'll need to pick, swing, boom, line out, set, swing back, boom back, pick, swing, boom, line out, set, swing back, boom back...well you get the idea very laborious.
Isntbard, I suspect that ignorance is the reason. I know many companies with certain names are doing a lot of things these days, but when I see a company whose name suggest expertise somewhere else...well I begin to wonder if they're biting off more than they can chew.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
MSNBC had a short report on the fallen girder tonight. A little more information but some different pictures that appear to be taken from under the existing overpass. Someone had reported something wrong with the girder about one hour prior to the failure. The report was taken by the authorities to be sign post causing a problem. The DOT spokeswoman said a sign post problem was found and corrected.
The pictures were taken from a different angle and shows what appears to be a kink in an otherwise smooth catenary bend. It also shows one of the braces which was quite long and as stated still attached to the girder. They also showed a picture of the girder just prior to the failure, but it was a such a long range and not very clear one could see nothing.
The May 18th Plain Dealer Newspaper from Cleveland OH had an article that said someone had called 911 before the accident happened. I don't have the article here but I thought it was like a day before the acident. The person calling had worked on bridge construction and said something was wrong. Somehow the dispatcher got the idea that a sign was out of place and nothing more was said about it.
From the newspaper article, it sounded like the problem was ongoing and not something that happened all of a sudden.
Good point about the contractor's experience or lack of experience Qshake. I read that contractor has done bridge work before, but it's hard to know how much was done by subs. They did have a sub for the steel erection on this project. CDOT uses a lot of prestressed bulb tee girders. The bracing required for a bulb tee during erection is much less than for a steel girder. If the contractor is comfortable with the minimal bracing for prestressed concrete girders it could have contributed to a mistake. This is just speculation but it's some thing to consider.
The big problem here is our legal system and engineers response to it. Everybody wants to pass responsibility and liability on to the next guy. In this case, CDOT passed responsibility for stability during erection on to the contractor. Was the contractor qualified to evaluate stability during erection?
Seeing this remonded me of another collapse- this one in Sudbury. Ontario - it happened May 7/04-
No-one was hurt but I understand a truck driver narrowly escaped as he was passing underneath
I haven't heard of any cause- only one picture at the bottom
Aren't bridge contractors required by the state DOT to have engineers or at least consultant engineers design the erection so as not to affect the bridge? A contractor shouldn't claim ignorance here.
This should also be reviewed by DOT engineers prior to any stage of erection.
I just checked the CDOT "Standard Specifications for Road and Bridge Construction" (aka the Barney book). There is no requirement to have an erection plan developed by a professional engineer and no requirement to submit an erection plan. A special provisions may have been included in the contract but I have no way of knowing that for sure.
CDOT probably does not want the liability of checking the erection plan. Many items that once required shop drawings now require working drawings. Working drawings are submitted "for information only" and will not be formally reviewed by the Engineer". One example is falsework. Falsework requires working drawings with a P.E. seal. These drawings are not reviewed by CDOT.
My purpose here is not to bash CDOT, but to point our a trend. I am sure other states are backing away from checking shop drawings and others design calculations. Consultants are trained by their insurance companies to avoid high risk areas. Everyone is trying to avoid liability. If nobody wants to be responsible how will things like girder stability be checked and future tragedies be prevented?
Isntbard,
My last position at my former job was in the working drawing review group of a state DOT. I imagine my experience is fairly representative of most DOT's:
All submittals required a PE seal and supporting calcs.
We were understaffed and very busy.
We had a prescribed maximum turn-around time on all reviews that we were measured on.
The contractors were constantly screaming to have their drawings expedited because the project was behind.
It was impossible to perform a detailed review of all submittals given these constraints.
Now, I don't necessarily think this alleviates the State from culpability because the State has an obligation to protect the traveling public, but the designer must bear responsibility as well.
In this case, somewhere in the chain an engineer needed to make a very tough and unpopular decision. Such as making the contractor take the girder back down because it was unstable without the second one, or keeping the road closed at rush hour until the second girder is placed, or the designer of the temporary bracing coming up with an extremely costly or complicated, but adequate, bracing system. Looking back, all of these are better options than the actual outcome. However, we've all been there in one form or another, with a tough decision to make, with financial and schedule implications looming, asking ourselves: "will that girder really rotate out and fail, or will it be OK for a couple of days?" We can't succumb to the easy out, our profession depends on it.
It is responsibility of the contractor/erector to assure that the structure is safely installed. The designer, or client (CDOT) could not predict which method of the erection the contractor would choose, and which (if any) braces be installed.
As I stated earlier, the accident occurred due to the improper bracing of a single girder, and according to the latest articles, it was never the intention of the erector to have single girder installed, so kind of temporary braces were used, as they run out of time and had to reopen the highway. Should they have a structural engineer on the site to oversee the erection? As hindsight the answer is yes, they should.
Commenting on the review of the erection plans/procedures by the State officials - state is contracting a completed bridge, and the only role for their engineers is to assure that the quality product is delivered. Checking/reviewing/approving of the erection plans will definitely make them liable, in case of failure, and they are not qualified steel erectors (or bridge builders). That's the reason why they are contracting this work out to a pre-qualified bridge company. And it's solely the erector's responsibility to assure safe erection.
I agree with wiktor and can understand the point made by ghghghgh....
I think there is common ground for what each of the aforementioned authors are saying.
In essence: While the State DOT will review certain drawings, the specifications if not specific special provisions state "...review by the engineer does not relieve the contractor of providing satisfactory results..."
Sure there is going to be some culpability on the part of the owner. That is just the way the legal system is...sue them all, those without much liability will usually pay a nusience fee and drop out.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
From what I understand, the CDOT representative on site gave at least verbal approval for the bracing system that was utilized. My guess is that they will not find his/her signature anywhere saying the bracing system was approved.
As I understand it, the bracing system was put in last minute because they didn't get the other girder up in time. The highway had to be reopened. Bad weather occurred the next day, then the weekend, then the collapse.
Terribly unfortunate accident. My prayers go out to the family of those killed and also to those who made the decisions in the field that day (if indeed that is determined to be the cause). I can't imagine what they must be going through as well.
I read the exact same story regarding the bracing/time frame. In my opinion, time should not have been a factor. Sure, we place restraints like that on contractors because we want lane drops for paving up before rush hour and the like, but this is something else all-together. If you're not finished with the erection as planned you have to continue until it is complete. I'm sure that in hindsight we'll all agree that a few more hours of delay during rushhour would be nice if we could bring back the unfortunate family.
Further, it obvious that the person approving the bracing at the job site really shouldn't have and has no business make such decisions.
A terrible tragedy.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
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