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RE: Masonry Lap Splices

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	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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