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Masonry/Rebar bond stress for lap splice

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I started looking at this yesterday.

Referring to ACI 530-02, it appears that Eqn 2-8 would give the best 
indication as to what bond stress was being considered in developing the 
equation.  (Excuse the following arithmetic.)

(Eqn. 2-8)     l(d) = 0.0015*d(b)*F(s)

If the bond stress is to develop the stress in the reinforcing, then,

      l(d)*pi*d(b)*F(b) = F(s)*pi*d(b)^2/4

where, F(b) is the allowable bond stress.

Rewriting, we have,

      l(d) = [F(s)*d(b)]/[4*F(b)] = 0.0015*d(b)*F(s)

Solving for F(b), 

      F(b) = 1/0.006 = 167 psi

So, it appears that ACI 530-02 says that bond stress is independent of 
masonry strength and is equal to 167 psi, regardless of masonry strength.

As far as splice length goes, Eqn. 2.9 indicates that the splice length must 
be 1.33 times greater than the development length, probably to account for 
the entire perimeter of the bars in the splice is not bonded to the grout.

Don't know if this answers anyone's questions, but the exercise was 
interesting!

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Al McPeters 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.  The references in ACI
. > 530 are from the 1920's and 40's.  Is it an empirical limit?   My
. > problem is a low grout strength (1810 psi). I am concerned with the lap
. > splice length in the wall and want to calculate an actual splice length
. > required for the applied load in the bar. I can't find a lap splice
. > length equation, other than for concrete, that includes the grout
. > compressive strength.  Building is 1996 BOCA so I have 48 bar diameter
. > splices.  I don't like the IBC splices as they are too long.  Thanks in
. > advance.

. > Al McPeters, P.E.
. > Senior Associate
. > amcpeters(--nospam--at)rlrpc.com

. > Robertson Loia Roof
. > Architects & Engineers
. > 3460 Preston Ridge Road
. > Suite 275
. > Alpharetta, Georgia  30005

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