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RE: Masonry Lap Splices

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Roland,

You are correct.  I must have had a brain cramp last night...I used the
area of the bar rather than the diameter.   That's what I get for
responding late at night.

HTH,

Scott
Ypsilanti, MI


On Sat, 13 Jul 2002, Roland Bokma wrote:

> 
> 	Thanks Scott for the reply (and others as well).  Just a couple of
> things, for the lap splices that you listed are they right?  Using the
> formula that you listed ld = 0.002dbFs (ACI 530-99 2.1.8.6.1.1, eqn 2-9).
> Using #6, Grade 60, bars wouldn't it be 0.002 * 0.75 in * 24000 psi = 36 in?
> This would give me a lap spacing of 7.2 inches which means I could use the
> adjacent core.
> 	The second thing is with the epoxy anchors, I've done this before
> but question it.  Sure, with the epoxy anchors, the strength of the new bar
> can be developed but how can the strength of the existing bar be developed?
> 
> 	As I look at the wall I'm analyzing, I have a regular footing and a
> tieback and the wall extends 24" above the tieback.  So I consider the wall
> pin (at the footing) - pin (at the tieback) with a cantilevered end (24"
> above the bond beam).  If I add a new portion on top of the existing using
> the epoxy anchors the analysis of the existing wall does not change does it?
> The new wall can be looked at as fixed on top of the existing wall, but the
> existing wall is still pin-pin with a cantilevered end with an applied point
> load/moment.  Does that make sense?
> 	What I would like to do is consider the wall pin-pin and extend the
> cantilever.  For this I would need to lap the existing #6 bars, correct?
> This led to the original question of does (2) #6 bars lapped alongside the
> original #6 bars (at 24" oc) equal (1) #6 bar lapped at 36"?
> 
> 	Thanks again,
> 	Roland Bokma
> 	Structural E.I.T.
> 	ProgressiveAE
> 	www.progressiveae.com
> 
> 	P.S.  I've contacted the MIM (Michigan Institute of Masonry) who
> contacted NCMA.  They suggested using (2) #4 bars alongside the #6 bar.  The
> #4 bar has a lap length of 0.002 * 0.5 * 24000 = 24 in.  So I could fulfill
> the 24" lap length in the 3 block course I  have over the bond beam.  The
> only problem with that is that I run into problems with the lap spacing (s =
> 24/5 = 4.8 in max), great.
> 
> > -----Original Message-----
> > From:	Scott Maxwell [SMTP:smaxwell(--nospam--at)engin.umich.edu]
> > Sent:	Saturday, July 13, 2002 1:55 AM
> > To:	seaint(--nospam--at)seaint.org
> > Subject:	Re: Masonry Lap Splices
> > 
> > Rick,
> > 
> > You are partly correct.  Section 2.1.8.6.1.2 of the MSJC (a.k.a. ACI 530)
> > states:
> > 
> > Bars spliced by noncontact lap splices shall not be spaced transversely
> > farther apart than one-fifth the required length of lap nor more than 8
> > in.
> > 
> > Thus, for grade 60 bars, the development lengths and permissible
> > transverse spacings for noncontact lap splices would be:
> > 
> > bar size	lap		transverse spacing
> > #4		12"		2.4"
> > #5		14.7"		2.9"
> > #6		21.2"		4.2"
> > #7		28.9"		5.8"
> > #8		37.7"		7.5"
> > #9		47.7"		8" (this is the first bar size that
> > 				    "trips" the 8" limit)
> > 
> > This is all assuming that you use the minimum required lap splice length
> > (0.002dbFs but not less than 12").  You could use larger lap splices,
> > which would allow larger transverse spacing.
> > 
> > You are also correct that the code is silent on whether or not you could
> > use a smaller lap splice if it was known that the actual stresses in the
> > bar were lower than yield/allowable.  The intent behind the current lap
> > splice provisions is the the lap splice should be able to fully develop
> > the strength of the bars, not just the actual load in the bar.
> > 
> > Jake's suggestion, however, is still a potentially valid one.  In theory,
> > you should be able to reduce the lap splice length if it was known that
> > the stresses in a bar would never exceed some value smaller than the
> > allowable stress, which would certainly be the case for bars at the top of
> > a cantilevered retaining wall.  It does seem, however, that the MSJC code
> > would not permit this.
> > 
> > I will second the suggestion that someone else made.  You should take a
> > look at epoxying in the new bars near the existing bars.  You could remove
> > the top two course to get back down the bond beam level.  Then drill near
> > the existing bars (use the permissible transverse spacing for lap splices
> > to determine how far you can be away from the existing bar) and epoxy the
> > new bar in the drill hole.  Take a look as some of the chemical (epoxy)
> > anchors such as Hilti or Rawl or others.  Embed the new bars in a hole
> > deep enough to fully develop the bars (see the manufacturer's
> > recommendations).  Then install the new course of block.
> > 
> > HTH,
> > 
> > Scott
> > Ypsilanti, MI
> 
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