I heard on the news yesterday that workers were trying to get the snow off of the roof. Thankfully, they were called off when conditions became dangerous.
But I don't understand why a roof in Minnesota needs to have snow removed in order to avoid collapse.
Daveatkins - Sure that doesn't make sense from our point (engineers) til you look at from an architect/builders/owners perspective: build it cheaper, faster. So then the engineer's have to come up with a manual that states what maintenance is required. Everyone at the meeting solemnly nods their head in agreeing to clean the snow. Then when it really counts they act like it never occured to them that maintenance would be necessary and certainly not due to their faster/cheaper mantra.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
Since the State, County and City, and the Met. Stadium Commission, spent the money and had the stadium built, they weren’t looking to gold plate it too. But, at the time it was built, it was state-of-the-art. I think it has deflated three different times, not all do to the fact that they didn’t shovel snow off of it, but I think two of them were do to snow.
We got about 16-20" of snow in about 18 hours, approx. 11:00p FRI. through 6-7:00p SAT. and had very strong winds from the north, thus lots of serious drifting. Certainly one of the top ten snow fall depths and blizzards in recorded weather keeping. I had 2 or 3' deep drifts in the driveway this morning. Several of the neighboring houses have approx. 4' deep drifts up on the south planes of the roofs. I weighed several blocks of it and it came in at about 9#/cf.
Now, look at Azcats’ video, at the underside of the roof, you see what is almost a quilted effect in the fabric, from the tension strands. There is an inner layer of fabric which you see, and a second outer layer of fabric, but they both show some form of this quilting effect. Thus, you get a fabric panel which is supported on three or four sides by cables, which can deflect down from snow load. Obviously, you will get drifting on the leeward side of the roof, and drift depth can increase as the fabric and cables settle, almost a ponding effect, but likely worse than would occur on a stiffer roof structure. Furthermore, the roof is warm enough so they do melt snow up there, adding to the ponding effect, and I think the video shows both snow and the water. They would have been warming the building for the game today, adding to this melting action.
The bigger question for most of us, structural engineers or not, but tax payers all, is why should we be financing these stadiums for a for profit business like the Vikings.
I wonder if "inexpensive" structures like pneumatic domes (e.g., the Metrodome) or tension fabric structures (e.g., the Dallas Cowboys practice facility)should be made illegal. I believe they meet the letter of the code, but they just don't seem to have the same redundancy and toughness of more conventional, rigid structures.
Generally the justification is that the facility provides large events that attract tourism, out-of-town visitors, etc. and that brings in money that benefits the citizens and businesses in the city.
Whether the numbers crunch out to prove this is the question. The numbers are difficult to pin down as there are all sorts of secondary effects from a stadium.
dhengr - I agree entirely with your rhetoric on the public building a facility for private business. However, as much as public outcry is had, the politicians always seem to know better what we need and don't need.
Usually the politicians will stand on the soapbox for the revenue it generates for businesses close by or for the city. But for NFL that's only what 8 weeks out of a year? Maybe 24 days if tourist spending Fri/Sat/Sun in town. And those are just the folks who actually want to see the sports team. There are typically many more taxpayers than those who actually attend the games. Also, the cities will typically provide a tax abatement to appease the owners.
Perhaps we should look back to Rome where the government built the stadiums. The team owners could then lease them or build their own (with their own money). I bet you fewer owners would building stadiums.
So many things here..
And this brings me to another issue - player salaries.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
Looks like the collapse occured after a leak developed in the synthetic material. Once the leak occured the roof deflated--so it seems.
Somewhat remeniscent of the Hartford collesium roof collapse. Space frame structure with no redundancy brought down by snow.
Grandiose ideas (space frame roof, inflatable) in the northen latitude with dire consequences (no lives lost though) to ultimately the taxpayers.
That storm was really a combination of two weather situations.
The first portion was an "Alberta clipper" (usually 2-4" of a quick dendritic snow followed by cold weather) that really had one wind direction. Later, a southern air mass with more humidity invaded the north and created most of the snow depth with different wind directions. The timing and sequencing of the snow and drifting were obviously a big factor.
The roof can be patched, but the stadium is old and is not needed to be a multipurpose sports stadium now because of other major stadiums built in the last year, but the other events and capacity are a big part of the financing and justification.
The site is in a prime location with infrastructure and access and sits on an almost perfectly level foundation of solid limestone about 15' below the surrounding level. During the initial construction, the underlying rock looked like a level concrete floor. With a lease on the pro football team (no other sports now)expiring within a year, there will be a lot of emotions, creative financing and design concepts on the horizon.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
Is there a provision in the building code for reduction of design slow load as long as the owner vows to keep the buildup of snow to a certain maximum? If so it seems patently absurd. Especially in a high-occupancy public facility. If this happens 8 hours later - what a disaster.
I completely agree with Dave Adkins above when he says that these structures lack the redundancy and toughness we expect, count on, and DEMAND in other structures. Either that or we plain don't understand how they work.
I wonder if they will consider replacing the roof with a more traditional "hard top" structure. They replaced the pressure-supported fabric roof at the University of Florida's basketball arena about ten years ago with a truss system. I realize the dead load would be a huge concern, perhaps they could replace it with some type of retractable roof that would have its own support structure.
The Florida Marlins new home is being built now in Miami and the roof structure sits on what looks similar to a viaduct (scroll down to see the gallery):
I agree with dhengr's prelim analysis, pretty much what I was thinking watching it. Also what tends to happen in other roof failures from snow and rain water ponding, a snowball effect
Slickdeals- SWEEEETTT! I almost killed my wife and I driving by it my last time down there. At first glance from the distance I was wondering what kind of weird highway bridge scheme Miami had come up with now. I am not much of a baseball fan and had no idea they were building a new stadium. Great project for your company, especially in "this economy".
You guys get the idea for those bridge-like roof girders from Figg's box girders that are all over Florida? Probably in some ways made the structural design a little simpler to make them a whole separate structure and build the stadium around it. Those cantilevered steel tree-column-screen-wall structures looked like no fun to design for 150mph...
Can you hook me up with a tour of the site? Beers that night on me? I'll be down there Christmas day
The Vikings have been kvetching about their "out of date" stadium for years now. They've threatened to move several times. It's not so much the roof as the revenue generators, like luxury suites and parking that they want.
I suspect this will be the straw that either gets them a new stadium or allows them to move. In my area we've built four major stadiums in the past 20 years. There's no money for schools or rest stops on the highways, but if a sports owner threatens to move, money flows from the skies. And each stadium will pay for itself.
I'll get off my soapbox.
Just a point about chicopee's post of 12 Dec 2037. The Hartford Coliseum was a space frame roof, but space frames should not be put in the same category as air supported structures. There was redundancy in that roof...what went wrong was eccentricity in the node design.
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