Analyzing Existing Metal Building 1

[StructTaco]

Anyone know of a software that easily models a preengineered metal building frame? I have to analyze an existing frame for additional loads and I can't find a tapered girder or column option in ETABS or Enercalc.

Thanks in advance

 

[mijowe]

I beleive RISA allows you to add custom tapered members.

 

[JAE]

Yes it does.

 

[MiketheEngineer]

Most PMBs use some very trying and almost exotic methods to show their buildings are good. Not sure I agree with many of them.

That said - I have also found there is usually little or no fat in these buildings. So adding ANY loads often blows them out.

Good Luck!!

 

[ToadJones]

STAAD allows for this as well

 

[JedClampett]

I entirely agree with Mike.
The PEMB designs go as far as to taper the members in a way that all of the sections just meet allowable. It's usually difficult to show that they work without adding any load to them.
Anytime we add any load greater than to hang a shirt on to an existing PEMB, we add an independent frame to carry the new load. If you're worried about the cost, think of the money that was saved initially by the design.

 

[ToadJones]

MiketheEngineer is right.
the PEMB and MBMA have their own standards.

 

[SteelPE]

I have a great method to analyzing metal buildings. I refer all metal building questions to another engineer who I have made acquaintances with. He was the chief engineer at a major company metal building company some years ago. This way I don’t have to figure out their wacky methods.

 

[StructTaco]

I was afraid of that. There are Z-purlins as well, I'm analyzing the addition of a fall protection anchor and none of the members are typical sections I'm used to dealing with in normal building design.

I hate these buildings as much as tilt-ups.

 

[StructTaco]

SteelPE, do you have the contact info for your acquaintance who knows metal buildings?

 

[mijowe]

We have had success in going back to the original (or another local) metal building designer and having them give us both help and good information to work with.

 

[MiketheEngineer]

Good luck w/ the fall protection anchor. If you have an "engineered" system -- shock absorbing lanyard, tested D-ring, etc., etc, you need to design for at least a 2,000 lb load. At least that is the best I have found. Our system tests at just less than a 1,000 lb load. OSHA says you can design for twice the anticipated load. Don't forget - that is for one guy ONLY. It is additive!!

Without that, OSHA states that you must design for a 5,000 lb load. Good Luck!!

Just tell them they can only fall when there is no snow or wind or rain or earthquakes around.

 

[OHIOMatt]

PEMB are a pain. I know that it is common (but typically not published) to set there unity stress checks at a minimum of 1.03 and even stretch that to 1.05 or 1.10 in certain circumstances. By a strict analysis, it would be likely that you could not justify the loads without adding anything.

On another note, I have seen PEMB were the collateral uniform dead load added is 0. They only use the self weight of the building and anythning that they supply such as insulation.

They have done a heck of a job in convincing people that their buildings are cost effective, but you get what you pay for.

 

[SteelPE]

StructTaco

I do have his contact information however; he only works in the New England area so depending on where you are he may not be of any help to you (he usually requires some sort of site visit). Most of my work is in New England so it is very convenient.

 

[dik]

Careful when you drill a hole in one of the members <G>...

I didn't catch the age of the building, but modification of it will void any warrantee you may have had. Some are so 'tightly' designed that modification may have an impact a couple of bays away... (Removal of an exterior 'leg'.)

Dik

 

[271828]

"Most PMBs use some very trying and almost exotic methods to show their buildings are good. Not sure I agree with many of them."

MBMA companies use the AISI and AISC Specifications as required by the building code. What exotic method from these specifications are you referring to? Or, are you claiming that they do not design per these specifications?

 

[StructTaco]

The client gave me the original drawings and calculations for the building...after I spent 8 hours yesterday pulling the rest of my hair out...

 

[mijowe]

I agree that they are really "efficiently" designed, but has anybody observed any major structural problems in PEMBs?

 

[StructTaco]

no I've never heard of a major structural problem with them. They just aren't user friendly for any modifications, and clients/owners always want to change things a bit...

 

[271828]

There have been some collapses in heavy snow. However, in every case I've seen, the snow exceeded the code prescribed load, so is that the fault of the MB manufacturer?

To be constructive and actually answer the OP's question: Several programs have tapered member capabilities. SAP2000 and RISA-3D are a couple of examples. These members are so easy to program that surely others have them also. However, beware that the programs most likely do NOT correctly do the strength calculations for tapered members. They also almost certainly do not correctly handle members with slender compression elements requiring Pn to be computed using E4 and E7 of the Spec. and Mn to be computed using F4 or F5 of the Spec. They also probably do not do Kx calculations correctly nor do they correctly do the Direct Analysis Method for such a building. Finally, there are other buckling modes such as constrained axis torsional buckling that are common in MBs and relatively uncommon (not as much as most people think, though) in conventional buildings and this mode is certainly not in typical commercial programs. Use the program to do the analysis and use manual calcs or spreadsheets to do the strength calcs.

Let me guess what's next. 3 or 4 guys will blame the programs' inadequacies on MBMA? Sounds like a bunch of gossiping women getting together to bash someone who's out of the room. Conduct that's beneath a group of licensed professioonals, IMO.