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RE: Deep Masonry Beams

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Mike,

The code deflection limit of L/600 can result in an incompatibility with the
curtain wall system.  You might need to limit deflection to what the window
mulls and gaskets can accommodate.

You will also need to increase the amount of reinforcing steel for the
aspect ratio of the panel.  A 6' x 31' panel will require more than the code
minimum reinforcing.

Your assessment of the lack of information for deep flexural elements for
masonry is accurate.  But your reinforcing will probably be governed by out
of plane wind / seismic loads.  I presume that the top of the curtain wall
will have out of plane environmental loads resisted by the bottom of the
lintel which can cause rotation on the lintel.

I would urge you to use "A" block as opposed to standard CMU block.  You
will get much better interlock when grouted.

Chapter 8 of the Army TM 5-809-3, October 1992 is specifically on lintel
design, and answers some questions on bracing.

Good luck.

Harold Sprague, P.E.
The Neenan Company
harold.sprague(--nospam--at)neenan.com


-----Original Message-----
From: Michael D Zaitz [mailto:mzaitz(--nospam--at)surfsouth.com]
Sent: Monday, October 26, 1998 2:01 PM
To: seaint(--nospam--at)seaint.org
Subject: Deep Masonry Beams


Does anyone have any experience in using a masonry lintel to span 31' 
over a window?  We have a client who is building a convience store and 
wants a 31' foot opening in the masonry wall (split face load baering CMU 
8" or 12").  We have approximately 6 feet above the opening to joist 
bearing.  Is there any problems with a 6 foot deep masonry beam?  I know 
in concrete there are special checks for deep beams for both shear and 
flexure but the ACI 530 code does not address this that I have found.  
Any concerns or pitfalls?  We are planning on a control joint near the 
end of the opening.

Thanks,

Mike Zaitz