Components & Cladding

[DCBII]

I've got an industrial steel building end-wall where cladding dumps the wind loads onto girts, which then dump the loads onto wind columns (pinned at both ends). These columns are about 130' high, and are spaced at about 25'-30' o.c. The tributary area to these columns ranges from about 3,250 s.f. to 3,900 s.f. The reaction from the top end of the column goes into the roof bracing system, which dumps it into vertical braced frames. Are the wind columns components and cladding? Or are they part of the MWFRS?

 

[jittles]

See ASCE 7-05 6.5.12.1.3. Any component and cladding element over 700 ft^2 tributary area is designed per MWFRS provisions.

 

[DCBII]

I just found that same paragraph in ASCE 7. Problem solved. Thanks.

 

[DCBII]

You know what's really confusing. ASCE allows you to use MWFRS for anything 700 ft^2 or more... but all there tables in the C&C section go up to 1000 ft^2. Smooth ASCE... Smooth.

 

[MiketheEngineer]

Thank god they don't build rockets

 

[ToadJones]

Those are some monster wind columns.

Big ole Crane building?

 

[TXStructural]

They may actually be building rockets in a building that big. Or at least airplanes.
I would be hesitant to build something that big (and housing the likely very expensive materials and equipment within) at minimum code. Buyers seldom understand the options to build stringer than minimum, nor do they understand that the code is intended only to protect life safety, not ensure ongoing usefulness if a maximum code-level event happens.

 

[SteelPE]

FYI, effective wind area can be calculated as (length^2)/3. So in this instance your effective wind area for figuring which wind equations govern (MWFRS vs C&C)your effective wind area is actually 5,633 ft^2.

 

[MrHershey]

Steel-

I've seen approaches like this thrown around, but have never seen where they come from. Is this in a code or textbook somewhere that you could point to as a reference? Reason I ask is we'll often be looking at one way concrete roof slabs or topping slabs for components and cladding and it seems overkill to consider the effective area of the whole thing. Would make more sense to do it based on span as you say, but I haven't been able to get a reference for that to justify it.

 

[OldPaperMaker]

MarkHirschi,
The process that SteelPE referred to is found in ASCE 7-05 in the Definations section 6.2 of Chapter 6 Wind Loads under "Effective Wind Area, A". In ASCE 7-10 it is found in Chapter 26, Section 26.2 Definations.

 

[ron9876]

However the criteria that jittles referred to is for tributary area not effective area. Also may want to read the commentary discussion on internal pressures for buildings with--I assume--large doors.

 

[JAE]

DCBII - I think what ron9876 just wrote explains the anomaly between the 700 s.f. tributary limit described in 6.5.12.1.3 and the charts that indicate effective ranges up to 1000 s.f.

You might have a roof truss that has a long span and a narrow spacing.

Example
Roof truss span = 50 feet.
Truss spacing = 8 feet.

Effective area = 50 x 50 /3 = 833 s.f.
Tributary area = 50 x 8 = 400 s.f.

The effective area is used ONLY to determine GCp values from the charts (which go to 1000 s.f.)
The tributary area is less than 700 s.f. limit so you would use C&C wind provisions vs. MWFRS provisions.