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RE: shear friction from horizontal top reinforcement, to resist holdown anchor pop out in A footing?

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Depends whether you are in a garage or not I would suppose.  Probably not for the particular application I am discussing.  I am actually going up to look at concrete spalling off corroded reinforcement without enough cover next week.


From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca]
Sent: Tuesday, October 03, 2006 2:59 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: shear friction from horizontal top reinforcement, to resist holdown anchor pop out in A footing?

Scott,
 
        You're from Alaska, therefore, I assume you know about the affects of salt on top steel of some structural elements.  Is there a possibility of chlorides (or for that matter any cause whatever) causing delamination of the concrete in the area of the top steel?  If there is you may not want to do what you are proposing.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
Sent: Tuesday, October 03, 2006 3:40 PM
Subject: RE: shear friction from horizontal top reinforcement, to resist holdown anchor pop out in A footing?

This question is driven by the ACI 318 requirement that anchors fail by ductile steel behaviour rather than concrete failure in a high seismic zone.  My opinion is that this code provision is a concrete industry conspiracy to smack steel buildings but creates the unintended consequence of slapping small wood buildings in high seismic zones in the process.
 
I haven't heard of a properly engineered llight timber frame in Alaska or California collapsing from this failure mode prior to the provision being written. Has anyone else?  Who was the guy that would say "where are the bodies"?


From: Haan, Scott M POA
Sent: Tuesday, October 03, 2006 1:28 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.