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RE: Lateral Deflection of Masonry Wall Building

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I usually use h/500 for PEMB with masonry walls.  The PEMB guys always cry.  What they really want is for you to verbally say a different criteria is ok without sending a formal addenda so that everyone bids it that way.  

I had a design build job where I spec'd that criteria.  The GC had already priced it for about h/240.  The extra stiffness caught him by surprise.  When I explained why I did it that way he totally understood.  He was able to bump it to h/360 but that was it.  The price difference between h/100 and h/500 was $0.25/sf.  It surprised me that the number was that low.  I have little sympathy for the PEMB guys now that I have seen that low of a number.

I always explain why I use the criteria I use and then given them the drift examples.  I further explain that the PEMB guy isn't the one who has to come back in 5 years  and deal with all the cracks.  The GC is able to say that the building is moving as spec'd and the PEMB guy is able to say that they meet their code.  That leaves it between the Arch, SE, and owner.  We just have to say that we told you so.  You didn't want the stiff building, we told you what it would do, and that's what it did.

John C. Jones, PE
Barnett Associates
Pell City, AL
205-884-5334
205-884-0099 (fax)


-----Original Message-----
From: Brian K. Smith [mailto:smithegr(--nospam--at)bellsouth.net]
Sent: Monday, December 01, 2003 9:03 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Lateral Deflection of Masonry Wall Building


Rich,

	H/400 is a good rule of thumb for a buildings with brick veneer, glass
curtainwall systems, or rigid interior partitions.  However, H/100 is
typically acceptable for a cmu structure used as a warehouse.  A good
reference on these items is AISC's Steel Design Guide Series 3,
"Serviceability Design Considerations for Low-Rise Buildings."

Brian K. Smith, P.E.

> -----Original Message-----
> From: rlewistx(--nospam--at)juno.com [mailto:rlewistx(--nospam--at)juno.com]
> Sent: Friday, November 28, 2003 8:11 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Lateral Deflection of Masonry Wall Building
>
>
>
> Several years ago I asked this question and got a good response.
> I was thumbing through my 2000 IBC the other day and came across
> Table 1617.3 - Allowable Story Drift.  For masonry cantilever
> shear wall the allowable story drift is 0.010*h which is equal to
> h/100.  For other masonry shear wall buildings the allowable
> story drift is 0.007*h which is equal to h/142.  Now I know this
> is in the seismic design section but Section 2108.5.1 refers to
> this table for story drifts in the general strength design
> section.  I don't have the text in front of me but I know there
> is an AISC manual on low-rise steel construction that would agree
> with these high sidesway values for masonry wall construction
> with steel framing.
>
> From my post several years ago I came away with the conclusion
> that most engineers design for wind sidesway of h/400 to h/500
> using the 10 year wind when masonry walls are present for the
> majority of the building.  As I wrote in other post I sent on
> slender wall design, I have a pre-engineered metal building with
> a 30 feet eave height.  The exterior walls will be masonry.
> H/100 for this condition is a 3.6" sidesway.  This seems too much
> for me.  H/400 would knock this down to 0.9".  I know this will
> increase the steel cost, but it seems to me that this is more
> appropriate for this conditions.
>
> What other opinions are out there regarding sidesway of
> pre-engineered metal building with masonry exterior walls?
>
> Thanks.
>
> Rich
>
>
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