Check of deflection and drift for steel hangar building

[h-badawy]

Greetings,
I am working on a project now as a design reviewer on the steel vendor, and we are clashing/fighting on two points in the serviceability checks as follow:

1-deflection
The vendor reference in the check of deflection is as per IBC2015 notes under table 1604.3 stating that "For secondary roof structural members supporting formed metal roofing, the live load deflection shall not exceed l/150" and I think the vendor reference is only for the purlin which can be secondary cold formed section but not for the main girder or rafter.
My reference regarding to deflection is table 1604.3 (roof Supporting non-plaster ceiling) L/240 LL and L/120 for DL+LL.

2-Drift (horizontal displacement)
The vendor guideline in the check of drift is as per AISC-2016-steel design guide#3 "Serviceability design considerations for steel buildings" table in page-30 the drift Serviceability considerations for cladding is(H/100) which is corresponding to the case that the cladding is supported by foundation.
but in the same table if we consider that cladding is supported by columns the value will be (H/500) which is matching with project case, moreover as per ASCE7-10 section#CC.1.2 "Drift of Walls and Frames" stating that: "Drifts (lateral deflections) of concern in serviceability checking arise primarily from the effects of wind. Drift limits in common usage for building design are on the order of 1/600 to 1/400 of the building"
I will appreciate your prompt advice and help on these two points

also see the attached of the screenshots from the codes references

Thank you

 

[dik]

I seem to recall 1:120 for deflections and 1:400 for lateral (several 747 hangars, been over 10 years since my last one)... with some PEMBs, I've seen deflections of 1:90 for deflections...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[h-badawy]

he tries to squeeze the size (material quantity) as much as he can two reduce the cost, even after sending him hundreds reference from many different codes, while his answer is I did many projects during last 25 years do you think I was wrong in all of these projects.

Thank you

 

[dik]

The deflection requirements that I posted are pretty much minimal... depends on the project. As I've noted PEMBs for some industrial buildings can be relaxed... on one, the horizontal lower girt was to provide lateral support for a 4' high masonry wall and L/90 wasn't acceptable.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[h-badawy]

Thanx dik

the PEMB-vendor informed me that MBMA standard described/elaborated the table of cladding drift in AISC-guideline as follow:

-For “pure” metal buildings without any partitions, brittle exterior walls, or frame-mounted equipment, story drift limits in the range of H/60 to H/120 might be adequate.
-For masonry or concrete exterior walls attached to metal frame, it is reasonable to use the story drift limits of conventional construction, such as H/200 for seismic loading and H/400 for wind.
-Where interior partitions are used or racking, bare-frame story drift is limited to H/500.

the thing is that what does he mean by racking and I don't if this case is matching with my building or not ,because he is using the first case above (H/60 to H/120).



Thank you

 

[jayrod12]

He literally means storage racking I'd bet. Like warehouse style racking tight up against the exterior walls/frames. They don't want the building sway to knock over the racks.

 

[dik]

So you attach the rack to the building and have stuff fall off the shelves...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[h-badawy]

thanks jayrod

but actually as per AISC-2016-steel design guide#3 , he defined the frame shape of deformation as a racking, moreover as per MBMA the definition of racking is the lateral movement parallel to the wall(cladding) but still not clear if that wall is attached from outside or inside the frame (most probably inside the frame).

Thank you

 

[jayrod12]

OP,

Racking has many meanings. When talking about building sway, it is racking. But in the context used in the bolded sentence (emphasis by me) I strongly believe they mean actual storage racking due to the fact that the rest of the sentence is talking about interior partitions, i.e. stuff inside of the frame.

-Where interior partitions are used or racking, bare-frame story drift is limited to H/500.