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Re: Roof Design Components and Cladding or MWFRS - ASCE7-02

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A quote from the commentary:
MWFRS - "Can consist of a structural fram or an assemblage of structural elements that work together to transfer wind loads acting on the entire structure to the ground.  Structural elements such as cross-bracing, shear walls, roof trusses, and roof diaphragms are part of the [MWFRS] when they assist in transferring overall loads."

C&C - Components receive wind loads directly or from cladding and transfer the load to the MWFRS.  Cladding receives wind loads directly.  Examples of components include fasteners, purlins,  ...  roof trusses.  Components can be part of the MWFRS when they act as shear walls and roof diaphragms, but they may also be loaded as individual components.  The engineer needs to use appropriate loadings for design of components, which may require certain componenets to be designed for more than on type of loading. (eg. long span roof trusses should be designed for loads associated with MWFRS, adn individual members of trusses should also be designed for C&C). ..."

To me, I interpret it that the roof truss, when it has cladding on it, will be designed for the MWFRS loading.  And when it is exposed, it will be designed for C&C.  But in the exposed case, there is only the tributary area of itself with the wind at C&C levels.

This is how I interpret.   Agree?

On 1/31/06, refugio rochin <fugeeo(--nospam--at)> wrote:
Oh, I've found it

On 1/31/06, refugio rochin <fugeeo(--nospam--at) > wrote:
But also the MWFRS is defined as " An assemblage of structural elements assigned to provide support and stability for the overall structure.  The system generally receives wind loading from more than one surface. "  These two definitions together seem to say, if the truss itself is taking the force for MWFRS, then it is not C&C.  I do agree that roof decking and connections need to be designed for the C&C.  But it is not clear otherwise.

Wesley, can you point out the page number or reference to the dual design?

On 1/31/06, Keith Pabst < kpabst(--nospam--at) > wrote:
I agree
Keith E. Pabst
-----Original Message-----
From: Wesley Werner [mailto:wwerner(--nospam--at)]
Sent: Tuesday, January 31, 2006 9:22 AM
To: seaint(--nospam--at)
Subject: RE: Roof Design Components and Cladding or MWFRS - ASCE7-02

    In the commentary where it gives definitions, roof trusses are listed under both C&C and MWFRS. My understanding of this dual listing is that trusses must be designed for C&C loading; and if they are acting as part of a frame or some other element in the MWFRS, they must be designed for those loads as well.

Wesley C. Werner

-----Original Message-----
From: refugio rochin [mailto:fugeeo(--nospam--at)]
Sent: Tuesday, January 31, 2006 9:03 AM
To: seaint(--nospam--at)
Subject: Roof Design Components and Cladding or MWFRS - ASCE7-02

I have a small fire to put out.

In design for wind on a roof, in the design of the trusses according to ASCE7-02, are these trusses to be based on Components and Cladding or on MWFRS?  We assume MWFRS because that is the main system for resisting wind.  However, Components and Cladding would indeed be used for connections and roof decks.  What are the engineers takes on these meanings?

Please reply ASAP.
Refugio Rochin, PE
Systems Engineering Ltd.