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Re: Torque vs. Tension in Bolts

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The point of my comment was that even if the plate is big enough to prevent
crushing of the wood allowing the tension needed in the bolt to be developed
the day of installation, it is quite possible that the tension will not be
sustained.  If it were new wood, the tension would probably not last a day.
Since this is renovation, this older and dryer wood may hold up a bit
longer.

Paul J. Martin, PE, SE
ADM Design Services
Decatur, IL
217-429-4412
-----Original Message-----
From: Peder and/or Cathy Golberg <golberg(--nospam--at)e-z.net>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Wednesday, July 14, 1999 11:14 PM
Subject: Re: Torque vs. Tension in Bolts


>Thanks to all for the formula that relates torque to tension based on the K
>factor.  I believe that's the formula I remember using when I had to
>pre-tension some anchor in the past.  The required torque on sleeve-type
>anchors is an option I will look into tomorrow morning for my particular
>application.  And yes, I do know that this formula can't be used for high
>strength bolts which is probably why I couldn't find this equation in any
>of my references.
>
>As for my reason for needed this equation, we have a seismic upgrade
>project of a school (1950's) with 8" concrete walls and wood roof.  Very
>little connection cuttently exists between the two.  For both in and out of
>plane support of these walls, we are adding (among other items) drilled
>anchors at 48" o/c in the existing 2x8 top plate down into the concrete.
>The existing condition is 1/2" cast in place bolts at at 6' o/c.  The
>properties of the wood determines size and spacing of bolts, not the steel
>or concrete strength.  We have been kind of vague on which type of drilled
>anchor to use, giving the contractor some choices between wedge, sleeve,
>and expansion anchors along with a couple different manufacturers.  The
>contractor has bought hundereds of 3/4" diameter RedHead Trubolt wedge
>anchors with standard washers (probably the least expensive product we
>pre-approved).  A little card that comes with the box of bolts states the
>torque shall be 3 to 5 turns of the nut or value in the table and also
>lists ONLY the minimum embedment depth.
>
>The special inspector and city inspector have both rejected the contractors
>bid to use the 3 to 5 turns and are requiring the 175 ft lbs of torque per
>the ICBO report.  As expected, the wood crushes before the torque is met.
>After talking to the techincal rep, the 3 to 5 turns is misleading as this
>relates to the tested torque achieved by bolting a steel plate to concrete,
>not other materials such as wood.  The 175 ft lbs is also really required
>to make the wedge anchor functional as per the manufactuer's requirements.
>
>As the existing wood plate can't be removed and reinstalled, I have used
>the provided formula and figured out that a 5" square plate is required to
>distrbute this 12,000 lb clamping force as to not damage the wood- maybe.
>The wood properties of this existing plate will surly not behave like new
>wood.
>
>It was looking earlier today like epoxy anchors are the only viable option
>unless the sleeve anchors/torque will work with the wood.  Of course, the
>contractor wants more money for the change although I don't see any change
>per the design documents, only installation requirements different that
>what they have done in the past.
>
>As to the card with the bolts listing only the minimum required embedment
>lengths - not good.  Standard embedments are required for seismic
>applications per the newer ICBO reports. Luckly I called out the embedment
>depth instead of just per manufacturer's requirements.  This is probably
>another reason why the contractors think that engineers overdesign
>everything.
>
>The contactor also has claimed that they have installed thousands of wedge
>anchors and never been told to torque per the ICBO (and manufacturer's
>values).  They always stop torquing when the wood starts to crush.  I have
>always assumed that the bolts are typically installed and set before the
>wood plates are installed and then the nut backed off and the wood put in
>place.  We haven't paid too much attention to this in the past but I bet
>there are many bolts not properly installed.
>
>
>Well, I learned something new today.
>
>Thanks.
>
>Peder Golberg, PE
>Portland, OR
>
>
>