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RE: Allowable Out-of-Plane Lateral Deflections of Masonry Veneers

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Response from NCMA:

Based on your reference to the 2000 IBC, I presume that you are working
with the 1999 edition of the MSJC Code (ACI 530 Code).  In the 1999
MSJC, the only general deflection requirements are for beams and
lintels.  There are no out-of-plane deflection criterion in the 1999
MSJC for masonry, which instead defaults to the deflection limits (which
in turn are a function of the type of finish material) in the IBC.  When
designing for components and cladding wind loads, the 0.7 reduction
factor would apply - but only to the deflection limits in IBC Table
1604.3.   The L/600 and 0.3 inch deflection limit in the MSJC is for
dead and live loads only, not wind loads.  Typically for masonry
systems, the out-of-plane wall deflection limit is L/240 (brittle
finishes) per IBC Table 1604.3, which for wind loads is checked against
100% of the main force wind loads or 70% of the components and cladding
loads.

In addition to the general deflection limits above, if the masonry is
being designed to Section 2108 (strength design) of the IBC, there are
additional deflection checks in Section 2108.9.4.6 - but these
deflection requirements do not apply to masonry designed by allowable
stress design (Chapter 2 of the MSJC).  

The only other set of definitive deflection limits are for seismic
design, which limits the story drift to 0.007h or 0.01h - depending upon
the type of shear wall system used.  

I hope this helps.  Certainly let me know if there are any additional
questions.

Jason

Jason Thompson
Director of Engineering
National Concrete Masonry Association
13750 Sunrise Valley Drive
Herndon, VA 20171
P: 703-713-1900
F: 703-713-1910

Matthew Stuart 
Structural Department
Manalapan
Extension 1283


-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com] 
Sent: Friday, March 02, 2007 12:14 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Allowable Out-of-Plane Lateral Deflections of Masonry
Veneers

You have had many good responses already.  Additionally, you may
consider 
using a 10 year wind for servicability as opposed to the 50 year wind
used 
for strength.  Servicability should not use the same force level as is 
required for strength.  This will give you the accepted L/720 for the 10

year wind, and about L/600 for the 50 year wind.

Regards,
Harold Sprague

>From: "Stuart, Matthew" <mstuart(--nospam--at)schoordepalma.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>Subject: Allowable Out-of-Plane Lateral Deflections of Masonry Veneers
>Date: Wed, 28 Feb 2007 11:45:50 -0500
>
>Back in the early 1980's I believe, when Architect's started to go with
>gage metal stud back up walls in lieu of CMU, the resulting flexibility
>of the metal studs resulted in a number of problems with masonry
veneers
>primarily as a result of water infiltration through the mortar joints
as
>the brick flexed to a point in which there was actual separation
between
>the brick and the mortar at the joint interface. The metal stud
industry
>and brick industry began pointing fingers at one another with the BIA
>responding with an H/600 criterion. Most design engineers at the time
>had trouble accepting this criterion because after all L/360 had worked
>for stucco finishes for some time. Never the less the H/600 got
codified
>into ACI 530 which adopted the criteria for vertical deflection only.
>
>
>
>Does anyone have any insight into the current lack of connection
between
>ACI 530 vertical deflection limitations and the current BIA
>recommendations for H/600 out-of-plane lateral deflection limitations?
>This is an issue because the ACI is a Code and the BIA provides
>recommendations only.
>
>
>
>D. Matthew Stuart, P.E., S.E., F.ASCE, SECB
>
>Senior Project Manager
>
>Structural Department
>
>Associate
>
>Schoor DePalma Engineers and Consultants
>
>200 State Highway Nine
>
>Manalapan, NJ 07726
>
>732-577-9000 (Ext. 1283)
>
>908-309-8657 (Cell)
>
>732-298-9441 (Fax)
>
>mstuart(--nospam--at)schoordepalma.com
>
>
>

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