Girder Falls During Construction
Girder Falls During Construction
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RE: Girder Falls During Construction
This failure looks very much to me like a lateral buckling failure under self weight. This check is often overlooked for composite beams, particularly by those using software to design the beam. Enercalc in particular does not check stability under self-weight during erection. I do indeed hope I am incorrect, and that some freak accident occured. Though, why it would occur several days after it was erected is unclear.
RE: Girder Falls During Construction
You raise an interesting and important point that I don't believe I've seen discussed here. Could you elaborate on the stability during steel erection issue or provide a few links or references?
Is the reason some engineers don't reveiw this because they feel it is a steel erection issue or because they don't see the problem at all?
RE: Girder Falls During Construction
My personal feeling is that the SEOR has to play some part in erection stability. I would break it down into components and systems. I feel the SEOR should be responsible to ensure that individual components (beams, columns, etc..) are individually stable under typical construction loads. The erector should be responsible to ensure that the system (masonry or steel framework) is stable as a whole.
By this I mean that the EOR should make sure that a beam will not buckle under its self-weight, and some nominal construction load, say 20 psf, prior to bracing by other beams or deck. However, the erector should be responsible to ensure that the partially erected structure is stable by providing temporary erection bracing. I would not expect an erector to have to brace an individual beam prior to fastening of the deck.
However, in the case of the girder collapse, the divider line becomes a little less clear. I think the engineer should check the stability of the girder. If a stability problem does exist, either he should adjust the girder shape to preclude instability, or make it explicitly clear on the contract drawings that temporary bracing will be required during erection. If the EOR takes the latter route, I think he is responsible for dictating where to brace the girder, and what capacity the bracing requires.
Now, as for whether this sort of check is required, well, I have found that this problem is most prevalent for lightly loaded (LL=40-80 psf)longer span composite beams. During erection, the beam is initially unbraced over the entire length. As the erector installs the metal deck, or builds up formwork for a concrete slab, the beam could see significant loading while unbraced.
I don't know of any links or references which talk about this issue. I just know I would not want to be the EOR in a case like this girder collapse, if they should discover that the girder had a potential for buckling under self-weight, and the engineer did not alert them to that fact.
I would love to hear input from others on the topic, but maybe we should move the discussion to another thread.
RE: Girder Falls During Construction
Thanks for the thoughtful reply.
One last question. You mention the fact that the software you use does not check for this stability condition, should it? Or, should the software at least make note of the fact that it doesn't check for certain conditions of use? Afterall, the software developer can't know all the uses of the members their software may design.
RE: Girder Falls During Construction
1)For shored composite beam designs, we would have a note that states the contractor is required to provide the necessary shoring. Since we do not design shoring, it would be his responsibility to hire an engineer that does. I would specify a max shored length requirement.
2)I think beams definitely should be able to resist buckling under their own weight. How can any bracing be attached if the beam can't even sit there by itself?
3)For unshored beam construction, I think what needs to happen is they need to incrementally weld down the deck first. Then workers can start walking on it and bringing up additional materials. Instead of laying down deck across any beam and people walking on it without it being welded down. This is easier said than done though.
However, if I am safe and put in add'l cross bridging on an unshored composite or non composite floor system (to resist construction loads before deck is welded), I am going to get a call "why do we have to do this we've never done it before". The owner would be notified and I would get a call from him about the additional labor cost.
RE: Girder Falls During Construction
Like other failures and when the smoke is settled, we will find out that many things went wrong in this disaster.
Construction safety and stability is a huge matter. It is so complex, there is no way that we can pin the responsibly on one entity alone.
I am currently working on a project where I have to demolish an existing load bearing wall to allow for any expansion of a building. The situation is very tricky, the schedule is ambitions to say the least and the fees are not adequate for the SEOR to perform the design. We could not find as-built plans nor were we allowed to do extensive field investigation because it would have required some destructive effort to ceilings and work place.
We developed a logical sequence of construction, detailed the final configuration. We have delegated the shoring design to the contractor. We are asking for signed and sealed calculations and plans to be reviewed by our office before they can proceed.
No one said it would be easy.
RE: Girder Falls During Construction
To qualify my statement I've more than 20 years on construction and design of heavy highway infrastructure. I've worked on many projects just like this one.
This is not an error on the part of a designer who didn't check girder stresses before the concrete slab was placed.
Where, pray tell, is the lateral bracing?! AASHTO requires designers, like it or not, to place cross-frames on 25' centers, needed or not. When I was a construction inspector (many, many years ago), the contractor was either required to devise a bracing scheme to tie off a girder or use the final cross-frames to tie it off. Moreover, most contractors I've worked with would not unhook the crane even though the its the end of the day and the pick was completed. If the girder wasn't braced, no one was going home until it was.
In the photo that I have, the splice is visible and the different sizes in top flange are also noticible. I would expect the section with the larger top flange to be placed over some intermediate support, in which case, would have smaller cross-frame spacing due to bracing requirements. Many state DOTs do not allow for a full composite section in the area over the pier (negative moment region) thereby not allowing for a positive mechanical anchorage for stability calcs. Moreover, the compression flange is on the bottom where it is not braced by the slab.
In my opinion, this was the work of a unknowledgeble contractor and, if the specifications were written like many others, also the fault of the inspector.
I hope a valuable lesson was learned...it certainly cost someone dearly...
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Girder Falls During Construction
This is a terrible tragedy.
RE: Girder Falls During Construction
http://www.denverpost.com/Stories/0,1413,36~53~2151748,00.html
Excerpt:
" The girder was temporarily braced to the existing bridge with five metal bars spaced along the 100-foot length. The bracings, fastened to the bridge with 8- to 10-inch bolts, came loose as the girder collapsed. CDOT had no explanation for the girder failure, Stegman said.
Although engineers did not have an immediate explanation for what happened, it appears that the girder "flipped from the bottom out," ripping the bracings out of the concrete as the structure fell onto the freeway, Stegman said.Contractor respected for work"
It appears that the the beam was braced. I think the article is a little confusing when it states that "8 to 10 inch bolts" as the diameter and quantity is more important than the length. Whether or not the bracing was adequate is another question.
I also read in a AP report that some representative blamed vandalism, although the police seemed to dismiss that.
RE: Girder Falls During Construction
Most likely those were 8 or 10 1" diameter bolts. But again, that assumes the reporter quoted contractor/engineer/inspector properly. Recall that most reporters are under the delusion that architects are responsible for buildings and bridges!
Once again, my experience is that single girders are picked with cross-frames attached, unless of course its the last one in a row. Some times contractors will elect to pick two girders at a time with a spreader rig.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Girder Falls During Construction
This sort of thing really worries me. In my experience, the senior engineers don't spend enough time passing on learned lessons to the younger engineers. It is a shame to let them learn the hard way. But the young engineers are usually too worried about "having a life" to spend time reading trade journals and learning things not covered at school. So they must take some of the responsibility as well. I am one of the lucky ones to start my career under an exceptional senior engineer with almost 50 years of experience. I learned many things working for him.
RE: Girder Falls During Construction
"Construction safety and stability is a huge matter. It is so complex, there is no way we can pin the responsibility on one entity alone."
There are many cases where responsibility can be "pinned" on one idividual, let alone an "entity".
Everyone wants to cop out when an accident happens. But the plain facts are, that someone, somewhere is responsible for every construction accident since man first stacked one rock atop another. Sometimes more than one individual is guilty, but very often one lone man makes a decision that cost's the life or lives of others. This is a fact that must be faced daily, and cloaking construction accidents in such a vast, murky shroud as you attempt, is trying to duck the bullet.
There is someone responsible, maybe several, but blame for these deaths will come to rest somewhere.
This work should be taken very seriously.
JTMcC.
RE: Girder Falls During Construction
Lutfi - you used a key word for building engineers - "seqence". We as EOR on structures may not be required to control the erection process, but we do a very good service when we include a sequence of events that are required to maintain stability on a structure during erection. We are the best positioned to identify those elements that are required before other elements are installed.
Bridges are designed somewhat differently than buildings in that most DOT's have very standard requirements for design plans, calculations, and construction. The Colorado DOT, I'm sure, has "systems" in place for most steel bridge structures. In this case, with a long span, perhaps their standard bracing, or the contractor's standard bracing, didn't cut it.
AISC does have some language within the Code of Standard Practice that outlines something about identifying on plans when steel frames depend on other non-steel elements to provide bracing or stability.
RE: Girder Falls During Construction
Pictures at the bottom of the article don't show much in terms of lateral bracing for the temporary condition (if the artist's rendering is correct).
RE: Girder Falls During Construction
RE: Girder Falls During Construction
The lateral load capacity of the inclined braces, especially towards existing bridge, is almost zero (until the braces were designed as fixed at both or at list one end).
RE: Girder Falls During Construction
Second most rapid 1 hour temperature increase - 9 am to 10 am - May 15
Most rapid 2 hour temperature increase - 8 am to 10 am - May 15
Most rapid 3 hour temperature increase - 7 am to 10 am - May 15
Most rapid 4 hour temperature increase - 6 am to 10 am - May 15
Suggested Area for Investigation: Lateral torsional buckling caused by forces from thermal expansion.
RE: Girder Falls During Construction
Kenny
RE: Girder Falls During Construction
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Girder Falls During Construction
http://www.indystar.com/articles/7/146963-2627-010.html
RE: Girder Falls During Construction
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 (http://www.pubs.asce.org/WWWdisplay.cgi?9000548). That could be a significant restraint.
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
RE: Girder Falls During Construction
"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!
RE: Girder Falls During Construction
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?
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
From the newspaper article, it sounded like the problem was ongoing and not something that happened all of a sudden.
RE: Girder Falls During Construction
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?
RE: Girder Falls During Construction
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
www.police.sudbury.on.ca/news/may0704.php
RE: Girder Falls During Construction
www.thedenverchannel.com/news/3324715/detail.html
ckenny
RE: Girder Falls During Construction
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.
Just my $0.02
VOD
RE: Girder Falls During Construction
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?
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
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.
RE: Girder Falls During Construction
http://www.denverpost.com/Stories/0,1413,36~23827~2324530,00.html
RE: Girder Falls During Construction
RE: Girder Falls During Construction
As for adding additional bracing or doing other things that may add a small amount of money to the job, our primary responsibility as structural engineers is to design safe structures. Economy is definitley a consideration, but it has to take a back seat to safety. Too many owners (and architects)don't care about this as they apply the thumb screws to get designs from structural engineers quicker and for less money, with the resulting structure as cheap as possible. I am writing this at 7:10 a.m. on Saturday to try to get another job out to meet an aggressive schedule. Again.
RE: Girder Falls During Construction
RE: Girder Falls During Construction
The "beam" is actually two (or more) girders bolted together end to end. One of those components was lifted backwards, so they then had to take it back down, turn it around, lift it again. Then when they got it back up, they put in the wrong bolts, and had to waste more time taking those bolts out and putting the right ones in. The result was they only had time to get up the one girder line and not the second parallel one. That's why they had to rig something up.
http://www.insidedenver.com/drmn/local/article/0,1...
http://rockymountainnews.com/drmn/local/article/0,...
http://www.constructionequipmentguide.com/story.as...
(plus various links alerady posted in this thread)
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RE: Girder Falls During Construction
RE: Girder Falls During Construction
Hg
RE: Girder Falls During Construction
RE: Girder Falls During Construction
This probably belongs in its own thread but...I think it should be mandatory for designers to spend a certain amount of time at construction sites and fabrication shops, even if it's not their own projects (which might be built too far away), in order to understand how those lines on paper translate into physical objects that real human beings and real pieces of equipment must somehow create under real conditions. (Number one: everything is always a LOT bigger than young designers expect it to be.)
("First, assume a perfectly spherical horse in a vacuum...")
A designer once joked with me that it's much better to work in design than in fabrication because "we can create designs on paper that you couldn't possibly achieve in a fabrication shop." He was kidding, but yet there's a certain amount of sad truth to that.
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