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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: "Truitt Vance" <Truitt(--nospam--at)adVanceEng.net>
• Date: Tue, 3 Oct 2006 14:58:04 -0700

Scott,

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.

Truitt

From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)poa02.usace.army.mil]
Sent: Tuesday, October 03, 2006 2:28 PM
To: seaint(--nospam--at)seaint.org
Subject: shear friction from horizontal top reinforcement, to resist holdown anchor pop out in A footing?

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 done.

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 together.

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