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# RE: Masonry lap length

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Masonry lap length
• From: "Scott Maxwell" <smaxwell(--nospam--at)umich.edu>
• Date: Thu, 19 Jul 2007 09:25:42 -0400

```2" cover would be about the bare minimum allowable cover...considering
typical 1 1/4" face shell thickness and a minimum of 1/4" clear for fine
grout and 1/2" for coarse grout.

Regards,

Scott

-----Original Message-----
From: Friis, Donna [mailto:FriisDL(--nospam--at)cdm.com]
Sent: Thursday, July 19, 2007 8:44 AM
To: seaint(--nospam--at)seaint.org
Subject: Masonry lap length

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

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.

--

Structural Engineer
Southern A&E, LLC

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