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# Re: embed bolts in CMU

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: embed bolts in CMU
• From: utej(--nospam--at)attbi.com
• Date: Mon, 16 Sep 2002 23:14:39 +0000

```Upon further review of ACI 530-02 (which is adopted with
additional requirements by the IBC) strength design
provisions, they have differentiated between the tension
capacity of a headed stud anchor and a bent bar anchor
in masonry.  Headed stud anchor are designed for the
lesser of the masonry capacity (Ban = 4*Apt*(f'm)^0.5)
and the steel capacity (Ban = Ab*Fy).  Bent-bar anchors
use the same two equations and add a third equation for
the strength governed by anchor pullout (Eq. 3-6).

In the ACI 530-02 commentary section 3.1.6.2, it
states "The tensile strength of a bent-bar A.B. is
governed by yield and fracture of the anchor steel, by
tensile cone breakout of the masonry, or by
straightening and pullout of the anchor from the
masonry.  Capacities corresponding to the first two
failure modes are calculated as for headed stud anchors."

In addition, ACI 530-02 section 3.1.6.1.1 states that
one is to calculate the projected area with the
following equation: Ap = pi*embedment depth^2
(Ap=pi*Lb).  Then it goes on to state that "The portion
of the projected area overlapping an open cell, open
head joint, or that is outside the wall shall be
deducted from the value of Apt.."

Therefore, ACI 530-02 and the IBC have addressed (1) the
anchor bolt tension capacity (greater if one uses a
headed stud anchor) and (2) it allows increased capacity
for deeper embedments as long as reductions in edge
distances are taken.

With this being said, does anyone know if Table 19-D,
regarding "Allowable Service Load on Embedded Bolts"
(which has been in the UBC since the early 70's) in the
1997 UBC and as Table 1912.2 in the IBC, allowable
embedded bolt in concrete load values are based upon
bent-bar anchors?  Most likely they are and, therefore,
headed stud anchors, or any anchor other than bent-bar
anchors, would receive an unwarranted penalty when
designed using this table.

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