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RE: Masonry lintel design

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I appreciate the various responses on this question - however, they tend
to reinforce my comment that there is no consistency in the industry.  

For side cover at CMU block, I assume 1-1/4" shell thickness and 3/4"
grout for 2" of cover.  But as Scott noted below, some sources indicate
that lintel block can be considerably thicker than 1-1/4" at the bottom.
The USACE design guide that Matthew referenced appears to use 3.38" from
the bottom of lintel to the center of bar; another source used 3.5" in
their design examples, which is what I have been leaning towards using.


John - if the NCMA design software defaults to 1-3/4" cover, that seems
rather unconservative.  I find it disturbing that the people who should
know CMU best would default to an unrealistic design value. 

Nels - I don't have a deep girder in this case - I have a 10-ft high CMU
wall and a 9'-4" high door with transom, and a roof truss supported over
the centerline of a 6-ft wide access door.  

I'm not sure I can even use the "nominal" course height of 8" since they
will likely fill the lintel block just to the top of the 7.625" block.
But I've initially used d = 8" - 3.5" = 4.5", which doesn't provide much
strength.  I have concluded that a single course masonry lintel will not
work due to excessive masonry stresses, but I wanted to find out what
others are assuming for "d".  

I likely will now try either a precast concrete lintel or a steel lintel
- I will also need to check deflection of this shallow beam. 


William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu] 
> Sent: Tuesday, May 09, 2006 3:08 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Masonry lintel design
> 
> Bill:
> 
> I also found an NCMA publication ("Architectural & 
> Engineering Concrete Masonry Detail for Building 
> Construction") in my library of books that shows CMU lintel 
> shapes as having a depth of 5 1/4" from top of CMU block to 
> top of bottom "shell".  This would leave the bottom "shell" as 2.375"
> thick.  Add 1/2" minimum for grout clearance and 5/16" for 
> half the diameter of a #5 and you end up with 3.1875" cover 
> from bottom of lintel unit to center of bar.  If you use the 
> full nominal depth of 8", then your d would be 4.8125".
> 
> Now, there is nothing to indicate in the publication that 
> this is a standard, minimum, or otherwise dimension.  But, it 
> is somewhat consistant with my previous suggestion of about 
> 3" of cover.
> 
> HTH,
> 
> Scott
> Adrian, MI
> 
> 
> On Mon, 8 May 2006, Scott Maxwell wrote:
> 
> > 
> ----------------------------------------------------------------------
> > ---- Your following message has been delivered to the list
> >   seaint(--nospam--at)seaint.org at 17:11:59 on 8 May 2006.
> > 
> ----------------------------------------------------------------------
> > ----
> >
> >
> > Bill:
> >
> > If you are planning on using an actual lintel shape block 
> (i.e. the "U"
> > cross section shape), then I would use a cover of no less 
> than around 3".
> > Considering your typical 8" block has a face shell of 1 
> 1/4" and a 12"
> > block as a face shell of 1 1/2", it makes sense to me that 
> the bottom 
> > "shell" of a lintel block will be about 1 1/2" or so.  At 
> is at least 1/2"
> > clear space for grout plus thickness of the bar, you end up 
> with 2.5 
> > to 3 inches of cover to center of bar.
> >
> > HTH,
> >
> > Scott
> > Adrian, MI
> >
> >
> > On Mon, 8 May 2006, Sherman, William wrote:
> >
> > > I am designing a single course masonry lintel using two 
> #5 bars near 
> > > the bottom of a masonry lintel block - what is a practical "d" 
> > > distance to use for vertical bending?  I have consulted numerous 
> > > references on masonry design but none of them give any guidance.  
> > > The lintel design examples show an assumed "d" distance - 
> with each 
> > > reference using different assumptions.  I need to get as much 
> > > capacity out of the lintel that I can, but I also need to make 
> > > reasonably conservative assumptions about the constructed 
> condition.
> > >
> > > (FYI: The masonry supplier has not been selected yet, so I do not 
> > > have accurate information on the dimensions of the lintel block.)
> > >
> > > (RANT: This is the most frustrating aspect of masonry 
> design to me - 
> > > the design formulas are well defined but the construction details 
> > > are not well defined.  It is very difficult to apply engineered 
> > > design to masonry, when the industry does not define such simple 
> > > "details".)
> > >
> > >
> > > William C. Sherman, PE
> > > (Bill Sherman)
> > > CDM, Denver, CO
> > > Phone: 303-298-1311
> > > Fax: 303-293-8236
> > > email: shermanwc(--nospam--at)cdm.com
>

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