I don't understand your steps 1 and 2. The 2.5
factor is applied to the factored design force, not to the "capacity of the
I believe that the intent is to allow design of the
anchor for a force less than the ductile failure load where applied loads
are significantly lower than the anchor capacity. For example, you may use
3/4" column anchor bolts as a minimum size but have relatively low uplift loads
on the anchors. The anchor embedment for uplift could be designed for
2.5*factored loads in lieu of the depth required for ductile
Seems like a practical alternative for
CH2M HILL /
Still trying to find some logic in
- Find the capacity of the
- Apply 2.5 factor to the capacity
and find the "backward-design" force.
- Apply the "backward-design" force
to the anchored structure.
- Find that the structure will fail
at a fraction of that force.
In most cases, this means that the
structure fails long before anything (brittle or ductile) will ever happen to
The failure of the anchored
structure appears to be the "trigger" embedded into the problem
Why are we designing the anchors
for the force that the anchored structure is incapable of resisting? Why
are we concerned about the brittle failure if the structure will fail in
whatever mode long before the anchor is be loaded to any noteworthy portion of
Is there logic here, after
V. Steve Gordin, SE
----- Original Message -----
Sent: Tuesday, February 03, 2009
Subject: Re: IBC Section 1908.1.16 is a
However, by code, you have to prove the failure mode is not
in the brittle failure and this is not limited to steel anchor only.
Therefore, if the failure happens in the concrete like breakout, pullout and
so on, 2.5 factor should be applied. 2.5 factor is kind of safety
factor to ensure that, when the brittle failure mode is governed, the
material is in the elastic range.
For example, if I use very strong
anchor (high capacity anchor), the concrete pullout strength will be
governed. Therefore, regardless of anchor type or material, 2.5 factor
should be applied.
In contrary, if I use relatively weak anchor and
the anchor capacity is governed "not concrete", 2.5 factor may be
On Tue, Feb 3, 2009 at 7:41 AM, Larry Hauer <lhauer(--nospam--at)live.com>
I haven't gotten any "post installed" anchors in
concrete to work using the 2.5 increase per CBC 1908.1.16, so I am falling
back on the definition of "Ductile Steel Element" from page 379 of the ACI
which states that ASTM A307 "shall be considered ductile." The way I read
ACI Sec. D.3.3.4, the A307 threaded rod, (for epoxy applications), or
anchor bolt would meet the criteria of this section, (I
Larry Hauer S.E.
Subject: IBC Section 1908.1.16 is a
Date: Fri, 30 Jan 2009 10:26:36 -0800
Now that new construction is
slowing down, I wonder how big of a role this will play in the remodel
Does anyone know the source of
the 2.5 factor mentioned in the modification to ACI 318 Appendix D.3.3.5?
It seems rather arbitrary to me. But, what do I know?
T. William (Bill) Allen,
V (949) 248-8588
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