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Julie Brown
New member
Username: jkbrown

Post Number: 1
Registered: 06-2004
Posted on Wednesday, June 23, 2004 - 02:18 pm:   Edit PostDelete PostPrint Post

BACKGROUND - For limiting framing member stresses and deflections of the curtain wall assembly I specified the following: Normal to the plane of the wall, deflection of framing members, including cantilevers, shall not exceed 1/175 of span length, but in no case more than 3/4 in., whichever is less.
The design was based on a 7-1/2 inch mullions, and this was in compliance with the specified manufacture's requirements (Arcadia).
Although the contractor wants to change the deflection requirements to L/240 +1/4 inch, if they are to go to a 7-1/2 in. mullion, because they sent in shop drawings for a different manufacturer and 10 inch mullions.

QUESTION - What thoughts does anyone have about this deflection change to the framing for the curtain wall?

There is no need to point out that the contractor is not complying with the specified manufacturer, because that beaten horse has died and the architect must live with their decision!!!
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues

Post Number: 276
Registered: 10-2002
Posted on Wednesday, June 23, 2004 - 02:27 pm:   Edit PostDelete PostPrint Post

Julie,

I think the L/175 is fine for non-glass supporting members, but I have always required that glass supporting members are additionally limited to L/300 of the glass length for the distance the glass is supported. And, deflections parallel to the wall not to exceed 75 percent of the glass edge clearances and other clearances between component parts.

From what it looks like, your deflection is changed from L/175 specified to L/240. I am not sure why you would be concerned about getting less deflection - other than that if its supporting glass it is still not adequate.

William
Curt Norton, CSI, CCS
Senior Member
Username: curtn

Post Number: 47
Registered: 06-2002
Posted on Wednesday, June 23, 2004 - 02:56 pm:   Edit PostDelete PostPrint Post

Masterspec lists L/175 up to 13'-6" and L/240 +1/4" over 13'-6" unsupported span, normal to wall plane.

It also limits deflection parallel to wall plane to 75% of glass bite.

If your dealing with the IBC you will want to have calculations to verify compliance with ASCE 7-98.
Julie Brown
Junior Member
Username: jkbrown

Post Number: 2
Registered: 06-2004
Posted on Wednesday, June 23, 2004 - 03:39 pm:   Edit PostDelete PostPrint Post

William,
Yes it is glazed, so it would be glass supported.
This project is in No. Calif.

Curt,
I will check on the size of this area. I do not have current drawings.
Yes, I have included the 75% for the deflection limit parallel to wall plane for glass bite.
This project is based on CBC.

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