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CMU lap splice

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Al wrote:

"Is there an equation to calculate the masonry bond stress for grout?  I
see the 160 psi listed as basis for the lap splice lengths in ACI 530
but can't find a specific reference for masonry."

ACI 530, p. C-19, C-20
They have development and lap splice equations.

Bond stress:

>From "Reinforced Masonry Design", 3rd Ed, Schneider & Dickey, pgs 206-207,
great discussion on the subject.

They quote "UBC Section 2409(c)5"
They say the ACI equations were developed from a bond stress of 125psi.

They list allowable bond stresses as:

100psi - No special inspection
200psi- Special insp.

I believe another way to calculate an EXACT lap splice which reflects the
actual flexural stress (fs) in your reinforcement is to calculate the stress
in the bars, then plug that into the lap splice equation. This will give you
a lap that develops that particular amount of stress in the bars.

HOWEVER, this may not be allowed by code, as you may HAVE to develop a
certain % of the bars allowable stress, usually the full Fs=24000psi for
Grade 60 bars. That is the way the formula is written anyway. In fact, requires at least 25% of bars in walls to develop Fs, but that is
for embedment I believe into the support, not lap splice.

I am sure Paul, Scott, Roger, etc., are more well versed in CMU and can
either add to or correct me on this.


Andrew Kester, EI
Longwood, FL

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