Drift or Horizontal deflection limits of rigid frames

[Qwikone]

Folks-
Hopefully you all can settle a disagreement. The subject is a steel rigid frame--roof only, and the discussion is whether the drift limit is H/60, or as the Designer quotes from the UFC-3-301-01 Structural Engineering Chapter 2 Modifications to IBC, 2-1.2.1 1604.3 Serviceability (Supplement)"in the wind design of a building or a non-building structure, the lateral drift shall not exceed H/480......."

Need this settled kind of quickly as the costs to provide for the H/480 are significantly higher than H/60, and may not be necessary at all for this situation.

I Appreciate any and all help with this one.......
Respectfully,
Qwikone

 

[rowingengineer]

I am very confused, but H/250 sounds like mid way.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[SteelPE]

I don't have this document "FC-3-301-01 Structural Engineering Chapter 2 Modifications to IBC, 2-1.2.1 1604.3 Serviceability (Supplement)" but I can tell you that usually H/480 would be for serviceability under wind loads for a multi-story building and is usually tied to the limit a person can perceive. H/60 would be a limit used by a metal building manufacturer on a single story building (don't know if I would use the limit but they probably would).

 

[patswfc]

It depends. H/480 sounds far too onerous and H/60 too much drift. If there is no client requirement to limit drift (e.g. cranes inside, etc.) then the main item controlling the allowable drift would be the cladding to the building and what it can accommodate. Attached is info from an old SCI publication (UK) with recommended drift limits for portal frames with different types of cladding. The limits range from h/100 (for metal sheeting) to h/300 (for brick). Hope this helps.

 

[structSU10]

The UFC are typically for structures designed for military use. If the structure is for military use, you must use the UFC criteria. In general, for deflection under at least 10 year MRI wind load, H/500 is what I use. It is a serviceability issue, so if partitions can handle it, if gravity members are designed for the P-delta effects, and so on then use what you feel is appropriate.

In ASCE they have inter-story drift limits for seismic, which allows for inelastic behavior (something that you don't have for wind, and probably wouldn't want) which are all around the H/50 and up.

Another point is that the P-Delta effects with H/60 would be very significant, both for the rigid frame and the gravity only system.

 

[TLHS]

The non-mandatory appendix to the steel code in Canada recommends h/400 or h/500 for most buildings and h/400 to h/200 for industrial building depending on the building construction, cladding, etc. That's assuming no crane.

 

[Qwikone]

Thanks guys for all the great input.
Some additional details I left out. StructSU10 is close--this will be a military structure. It is actually an open "sun-shield" with no siding. Basically a steel frame 24' high open sides and a 4/12 pitch standing seamless metal roof.
We are submitting a proposal for a less stringent drift requirement than H/480 as the serviceability doesn't warrant stricter requirements in this case. We have proposed H/250 to the Base as a compromise solution.
I'll let you guys know what happens....................
Qwik

 

[Qwikone]

Just noticed....its standing seam, not seamless.....

 

[rowingengineer]

sounds good to me

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[Qwikone]

Update--
The Base accepted the H/250 for this case.
Thank you for all your help and suggestions!!
Qwik

 

[Agent666]

Are you sure the h/60 isn't the ultimate limit state drift limit. Close to a 1.5% drift limit which is used in some codes for ultimate drifts vs serviceability drifts. I am not familiar with the code referenced.