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RE: embed bolts in CMU

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These relatively new formulas for hooked rods were first presented in the
NEHRP Provisions (I believe it was the 1997 issue) masonry section, and were
predicated on some Univ of Illinois research performed in about 1995.  The
hooked anchor rod formulas were empirically based.  They were modified from
the research because they placed no upper bound on the strength that you
could get due to the hook.

I continue to be a bit troubled in that the testing was done on concrete not
masonry.  The f'm were deemed to be close enough to f'c, but I have always
been bothered by that one even more.  But there is a very healthy factor of
safety.  I would feel a bit more comfortable if a prism was cast from
concrete and tested to somewhat  corroborate the f'm to f'c, but I have
never seen this done.

I would have also liked to have seen the anchor rods with and without a bond
breaker.  The steel to concrete bond is too variable to be reliably used.
That is the reason that bond to plain steel was dropped by ACI 318 when the
1963 version was superceded.

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	utej(--nospam--at)attbi.com [SMTP:utej(--nospam--at)attbi.com]
> Sent:	Monday, September 16, 2002 6:15 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re: embed bolts in CMU
> 
> 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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