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RE: shear friction from horizontal top reinforcement, to resist holdown anchor pop out in A footing?
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: shear friction from horizontal top reinforcement, to resist holdown anchor pop out in A footing?
- From: "Haan, Scott M POA" <Scott.M.Haan(--nospam--at)poa02.usace.army.mil>
- Date: Tue, 3 Oct 2006 14:37:57 -0800
There are some engineers
with whom reason does not apply and believe codes are the engineering Koran
[Torah or Bible or The Origin of Species depending on religious
There is a real simple
solution to the non-problem of small wood buildings collapsing from concrete not
popping out at light timber frame building holdown anchor bolts. The
solution is to add an exception to the ACI code that says anchors are not
needed to fail in ductile yielding prior to concrete failure for
holdown anchors in light timber frame buildings. Someone did not
like my proposal for this at the last ACI code adoption and local code
. I want to know which properly designed wood building collapsed because
of this failure mechanism and prompted the ACI code
Punching goes both ways up or down. I think if
you put a plate on the bottom of an anchor at the bottom of a footing pushing up
the force would be less than the downward force on the post on the end of a
shearwall when you add the gravity loads to the lateral overturning force at the
end of a shear wall - granted some of the force goes directly in the soil
I wonder the same thing, I agree with you and hope someone
on this list can explain why this doesn't work...or why its a bad idea. I
believe what you are describing is more commonly referred to as dowel action, or
using longitudinal steel to resist shear? This came up on the list a
couple of months ago when someone was wondering if they could use it to resist
punching shear on a thin (too thin) flat plate, that is the same concept.
I posted that specific question as but didn't get a response. I also
remember learning about dowel action in school...for whatever thats worth...but
it seems to be completely ignored in practice.
Others do use it though, either that or just get the values
through testing (then shouldn't you be able to calculate
the capacity?) - note that Simpson requires a #4 bar within 5" or so
on all of their SSTB's when installing them in a stem wall. I highly doubt
they would require it if it didn't do something. You should bring that to
the attention of the engineer you were speaking with and see if he has an
opinion about it.
I have just assumed it was just considered bad practice to
use it because I have never seen a good way to calculate it, although there is a
lot of papers written on it, so I just use the shear cone, or develop the
holdown in to the foundation w/ rebar or a longer all thread.
Can you use
horizontal reinforcement in the top of a footing to resist the pop out of a
concrete tiedown anchor rod? I talked about this idea
with an intelligent engineer and he said it can't be
I drew a free body
diagram of a pop out cone with the reinforcement developed in the cone and with
the shear friction parallel to the cracks with the vertical of shear
friction component cancelling out the upward force and the horizontal component
cancelling out. I'll e-mail a .pdf of the solution if someone wants to
look at it and tell me where it goes South.
He said the tension
is acting vertically across the inclined crack failure plane, and you've
got the shear component parallel to the crack and tension component
perpendicular to the crack, and that the shear friction formula in
ACI 318 for reinforcement at an angle to the crack only applies to
force component parallel to the crack.
This is where my
head starts hurting assuming the free body diagram is inappropriate, couldn't
you still increase the amount of horizontal reinforcement across the crack to
cancel the horizontal component of tension perpendicular to the crack and add more shear friction for the component parallel
to the crack ect...etc....
I don't believe horizontal reinforcement couldn't clamp concrete from
popping out with enough horizontal reinforcement clamping the pieces