Metrodome Roof Collapses?

[SunBat]

Much more.

She goes to Texas A&M. A school known for it's engineering. It is also one of the top 3 in the nation for Meteorology.

Broad generalities are misleading.  What kind of engineering?  What specialty in meteorology?  These questions must be answered to know for sure.  I can see meteorology requiring a good amount of math though.  I think it would be a really cool field to get into. 

[Masherbrum]

Until Mother Nature throws a curveball.

[SunBat]

Until Mother Nature throws a curveball.

I don't have the time to get into the specifics but the codes that specify the environmental loads and the material design codes are specifically written to address when mother nature throws a "curveball". Having said that, in every design there is always a small probability of failure and as long as the engineer has properly designed according to all applicable codes, then they have a chance of being exonerated. I would be willing to bet though that this was not the case with this failure for the main and simple reason that many others roofing structures would have failed in the area.

[Dichotomy]

When designing a building what codes do you use or are the most prevalent? Also how do you determine the amount of wind / ice / etc loading to consider in your design?

[Masherbrum]

Clearing a domed roof off with 7 fires in temperatures around 20 degrees with heavy snowfall is asinine.  This was obviously "recommended care" passed along to the site of the HHH Metrodome.

[SunBat]

When designing a building what codes do you use or are the most prevalent? Also how do you determine the amount of wind / ice / etc loading to consider in your design?

The short answer is that most states and cities have their own building codes.  However, most of these building codes refer to “the latest version” of ASCE-7 – “Minimum Design Loads for Buildings and Other Structures” for the derivation of environmental loadings such as wind, snow and seismic.   The various materials of construction such as Steel, Concrete, Wood, Aluminum, Masonry, etc, etc each have their own codes that provide methods to determine strengths of the various structural components that compose the structure.  The engineer has to analyze the structure under the imposed loads to determine the stresses in the structure and then make sure that each component meets the material code requirements.

[SunBat]

Clearing a domed roof off with 7 fires in temperatures around 20 degrees with heavy snowfall is asinine.  This was obviously "recommended care" passed along to the site of the HHH Metrodome.

If the owners agreed to maintain the roof in that way, they should have done it or had the roof modified to accomodate their maintenance requirements - of course that would have cost money because they would need to hire engineers to revise the design and then pay to have the modifications installed.  Instead they probably had someone like Dred advise them that the engineers were "uptight and incompetent and the entire structure is way over designed" and since they were accountants and business men, they were way smarter than the engineers and they agreed with Dred that the engineers were idiots - right up until the moment the roof fell down.  Now it's really going to be expensive.   

[Dichotomy]

Thanks

As I said previously, I do find discussions of structural engineering and techniques fascinating. There's none of it, in my opinion, that isn't worth having at least a passing knowledge about.   

[grizz441]

When designing a building what codes do you use or are the most prevalent? Also how do you determine the amount of wind / ice / etc loading to consider in your design?

Clearing a domed roof off with 7 fires in temperatures around 20 degrees with heavy snowfall is asinine.  This was obviously "recommended care" passed along to the site of the HHH Metrodome.

ASCE Chapter 7 gives design procedure and values for snow loads based on U.S. location.

Where do these values come from?  This is a complex issue and you creep into the concept of Structural reliability/probability.  The core concept of reliability is minimizing the probability of failure while maximizing safety.  The more "safe" you make a structure the more costly it becomes and economically unfeasible.  The acceptable level of safety in structural components such as the metrodome is probably in the realm of Beta Value between 3.5-4.0  This is basically just a statistical Z value.  Such values would give a PF between .000233 & .0000317.  You basically back calculate what your design loads need to be based on the statistical probabilities.  Snow fall can be idealized as an Extreme Type 1 Gumbel Distribution: http://www.itl.nist.gov/div898/handbook/eda/section3/eda366g.htm

Based on what your load resistance model is, you can do testing to see what kind of distribution it will also have.  Then you run Monte Carlo Simulations, ala, hundreds of thousands of runs with random variables to see what the probability of failure is, and then back calculate your design snow loads to make sure this probability of failure is an acceptable value.  

So yes, engineering is a science and these design values have incredible merit.  As long as everything is designed, constructed, and maintained as design specifies, then the probability of failure should be slim to none and would require a "perfect storm" of events to take place for it to fail.  A perfect storm combination would include: A slight human error in calculations, a very large load, a slightly damage component.  Or something to that effect.  Or, the storm of the century.  Was this the most epic storm Minneapolis has ever seen?  Did it set some century old record?  Not that I'm aware of.  


Ground snow values for United States.
Desisn is based on 50 year extreme's.

[Dichotomy]

Thanks Grizz.

Do you consider a reduced wind based on snow / ice accumulation?

I just checked Minneapolis in the ANSI/TIA/EIA-222-G and it's showing a 90 mph maximum wind. 

[grizz441]

Thanks Grizz.

Do you consider a reduced wind based on snow / ice accumulation?

I just checked Minneapolis in the ANSI/TIA/EIA-222-G and it's showing a 90 mph maximum wind.  

Yes minneapolis has a design wind of 90mph.

Sort of, that's where load combinations come into play.  For all practical purpose, while there may be some correlation with the storm of the century, the max wind load will not occur at the same time the max snow load occurs, and also at that same time, an earthquake hits minneapolis.  

These would be the appropriate LRFD load combinations if Wind and Snow were both acting on a component:
Take the worst case of these:

3. 1.2D + 1.6(L_r or S or R) + (L or 0.8W)
4. 1.2D + 1.6W + L + 0.5(L_r or S or R)

ASD would be:

D + H + F + 0.75(W or 0.7E) + 0.75L
+ 0.75(Lr or S or R)

[grizz441]

Much more.

She goes to Texas A&M. A school known for it's engineering. It is also one of the top 3 in the nation for Meteorology.

I don't doubt it requires a lot of math but idk about that.  I have taken calc1-3,diff eq, matrix theory, statics&dynamics courses, structural analysis, structural statistics...  Only math class I haven't taken is numerical methods.

I'm pretty sure all of those, aside from matrix theory are required.

[Dichotomy]

Thanks again Grizz.  I probably won't ever be a full blown engineer but I can be somewhat useful if my knowledge base is broadened 

[Shuffler]

I did not delve into it. I am going on what their Calc professor told them all in class.

When told what she had to take the engineering students were very surprised.

I'm figuring like anything else. You learn it the hard way in school then when in the job arena you have computers do most of the calcs. You must be able to understand what is being done though.

[Dichotomy]

You hit the nail on the head for me Shuffler.  I got roped into running a program that designs structures 4 years or so ago.  Fortunately I've had the guidance of a PE I've worked with for almost 15 years and he's helped a LOT.  As I'll never actually be a full blown structural engineer I try to learn as much as I possibly can about it.  Not only in my area but as many other areas as I can.  Which is why I'm bugging Grizz and Sunbat as much as I can (sorry guys).