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RE: Masonry lintel design

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Bill:

I have to admit that as soon as I read the specific information that you
offered to show Nels that it was not a deep girder (i.e. that it was an 8"
high lintel supporting a truss reaction), the situation screamed to me
"use a precast lintel" before I even got to the end of you message (and a
whisper of "use a steel lintel" was not far behind but but the end of your
message beat the whisper).  My experience has taught me that a single
course lintel does not take very much to be "over-whelmed".

As to d for a lintel, I suppose that you could also always use a knock-out
block shape installed upside down to get a deep d value.  This could
create some grouting issues as now the tapers of the face shell and webs
would be inverted, but should not be a big issue for a single course of
grouting (i.e. your single course lintle).  It also adds to the complexity
of the installation as the contractor would have to have some sort of a
form below the lintel to close off the bottom (i.e. something to support
the grout), but since the CMU lintel would likely need shoring to support
it until it was strong enough to be self-supporting, it is likely (again)
to not be a huge issue.

In the end, from your more detailed description that you provided to
address Nels comments, I would have to say that a steel beam or a precast
concrete lintel make the most sense to me.  If this is the only place
where a precast lintel would be required, then likely a steel beam would
be the logical choice (i.e. economies of scale and not having to
potentially introduce another trade onto the project).

Regards,

Scott
Adrian, MI


On Tue, 9 May 2006, Sherman, William wrote:

> 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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