I am interested to know what masonry cover you use for bond beam corner
bars or vertical filled cells with 2 bars (1EF). It seems like the K
value would be quite low say 2" and hence the lap length very long
(since our value it is divided by K.) Or am I missing something?
Donna
Adam wrote:
The ACI530-99 code had only ASD included with the ld = 0.002*db*fs
equation. However, the 2000 IBC over-ruled this equation and used the
more cumbersome equation ld = 0.16*db^2*fy*gamma/(K*fm'^1/2). In
addition, the 2000 IBC included a procedure for strength design that had
a similar equation for ld. According to one ACI530-99 committee member
it was a mistake to use the latter equation for ASD, it was only
applicable to strength design. I agree with Bill Sherman that this does
not make sense.
The ACI530-05 uses the equation ld = 0.13*db^2*fy*gamma/(K*fm'^1/2) for
both ASD and strength design. Now, the 2006 IBC overrules this equation
for ASD and reverts to ld = 0.002*db*fs with the important exception
that when the calculated stress in the bar is greater than 80% of the
allowable stress then ld shall be increased by 50%. I don't know about
you, but almost all of my masonry designs result in steel controlled
sections when using ASD, thus ld must be increases by 50%.
The IBC uses the equation ld = 0.13*db^2*fy*gamma/(K*fm'^1/2)for
strength design. This results in shorter lap lengths (most of the
time). Therefore, I have now begun using strength design for masonry.
This has resulted in much more economical designs in overall rebar use
as well as lap lengths.
--
Adam Vakiener, P.E.
Structural Engineer
Southern A&E, LLC
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