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Re: Masonry Lap Splices

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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

On Fri, 12 Jul 2002, Rick Burch wrote:

> Jake, 
> I've seen people reduce the lap splice as you mentioned, but I don't
> recall specifically seeing this in the ACI 530 code. Is it in there
> somewhere?
> 
> Also, I think ACI 530 permits bars at lap splices to be separated by up
> to 8 inches, so, surprisingly, the bars can actually be in adjacent
> cells. I don't have my code at home so I can't quote the section, but I
> feel sure it's in there.
> 
> Rick Burch
> Columbia, SC
> 
> 
> 
> Jake Watson wrote:
> > 
> > Do you need a full lap splice?  You can shorten the required splice by the
> > ratio of the actual stress in the steel vs. the maximum allowed stress.  For
> > example, if you only have 12ksi in your bar, the required lap length would
> > be 1/2 that required at 24ksi.  
> 
> 
> > Some other thoughts, it is only a lap splice when the bars are relatively
> > close to each other.  The number of 5 bar diameters comes to mind, but you
> > should look it up.
> 
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