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RE: Tension equations for anchors in CMU
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- Subject: RE: Tension equations for anchors in CMU
- From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
- Date: Fri, 5 Nov 2004 21:54:21 -0500 (EST)
Joe: Yes, that is what the code appears to say. In other words, Eq 2-4 is rather conservative. I did pose the question to someone on the committee. Here is his response: "In my personal opinion, Eq. 2-4 is too conservative. If augmented by minimum cover requirements, Eq. 2-3 is enough. That's the way the strength provisions are written, and I would use those for anchor design. We didn't have time to fix this for the 2005 provisions. We hope to finish harmonizing the ASD and SD provisions for the 2008 document." HTH, Scott Adrian, MI On Fri, 5 Nov 2004, Joe Grill wrote: > Scott, > Until recently, I've never had to calculate tension values in the top of a > CMU wall. So what you are saying is that if you have an anchor bolt (with > tension) at 3" from the edge of the wall then Ap=28.3 sq. inches and a > pullout strength of only 550# even if the anchor has an embedment of say > 10". The strength design approach makes way more sense in that the > truncated edge would be there but Ap would be much larger around 150 square > inches for a 10 in. embedment in a 8" wall. > Joe > > Joseph R. Grill, P.E. (Structural) > Shephard - Wesnitzer, Inc. > Civil Engineering and Surveying > 1146 W. Hwy 89A Suite B > Sedona, AZ 86340 > PHONE (928) 282-1061 > FAX (928) 282-2058 > jgrill(--nospam--at)swiaz.com > > > -----Original Message----- > From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu] > Sent: Friday, November 05, 2004 12:03 PM > To: seaint(--nospam--at)seaint.org > Subject: Re: Tension equations for anchors in CMU > > Joe: > > I doubt it is a typo...if so, then it is a typo that has existed since the > 1995 edition of the MSJC (ACI 530/ASCE 5/TMS 402). So, I have to believe > that if it was in fact a typo, that SOMEONE would have caught it in the > past 9+ years. > > I believe eq 2-4 is the allowable stress method for a necessary "cone > breakout strength" reduction when the anchor bolts are too close to the > edge of a wall relative to the embedment depth. In such a case, the > "breakout cone" will be truncated. > > It likely does not "match" well with the similar provisions in the > strength chapter as they have not really been "coordinated" as of yet (to > my knowledge at least). So, the strength chapter handles that reduction a > little different. > > I will ask someone that I know on the committee for their thought. > > Regards, > > Scott > Adrian, MI > > > On Fri, 5 Nov 2004, Joe Grill wrote: > > > A couple of days of slack time have prompted a flurry of posts to the list > > by yours truly. Today, I'm trying to put together a small spread sheet > for > > allowable tension for an anchor in the top of a CMU wall. Not a big deal > > for hand calcs, and I've done this a number of times, but I'm trying to > > minimize embedment requirements for holdown anchors possible being a > little > > more "custom" from job to job as embedment depths I've called out before > > tended to be pretty conservative for more lightly loaded holdowns. Most > > stem wall construction around here is CMU. > > > > > > > > I hadn't noticed this before, but equation 2-4 in ACI 530/02 uses l sub be > > for one determination of A sub p. The definition for l sub be seems > > incorrect for the tension application and should be used for shear > > applications toward a free edge. The strength design section uses l sub b > > for calculating A sub pt. The definition for A sub pt and the explanation > > for overlapping cones and deduction of areas of A sub pt which fall > outside > > the masonry surface, seems to make more sense, and I think should be used > in > > the service load equations also. Is there a typo error? Has there been > any > > errata's? The way equation 2-4 is written seems extremely conservative to > > me. > > > > > > > > So, wazup? > > > > > > > > Thanks, > > > > Joe > > > > > > > > > > > > > > > > Joseph R. Grill, P.E. (Structural) > > > > Shephard - Wesnitzer, Inc. > > > > Civil Engineering and Surveying > > > > 1146 W. Hwy 89A Suite B > > > > Sedona, AZ 86340 > > > > PHONE (928) 282-1061 > > > > FAX (928) 282-2058 > > > > jgrill(--nospam--at)swiaz.com > > > > > > > > <http://inet/index.htm> > > > > > > > > > > ******* ****** ******* ******** ******* ******* ******* *** > * Read list FAQ at: http://www.seaint.org/list_FAQ.asp > * > * This email was sent to you via Structural Engineers > * Association of Southern California (SEAOSC) server. To > * subscribe (no fee) or UnSubscribe, please go to: > * > * http://www.seaint.org/sealist1.asp > * > * Questions to seaint-ad(--nospam--at)seaint.org. 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