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RE: Embedded Anchor Bolts In Compression[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: RE: Embedded Anchor Bolts In Compression
- From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
- Date: Wed, 25 Oct 2000 09:49:30 -0500
Mark, Forgive me for I have sinned, but I have also designed for concrete bond to plain steel. But after I witnessed the pullout in 1978, I investigated the basis of the ACI 318-63 bond. After that, I never returned to the world of bond on plain steel, neither did ACI 318. I agree that bond exists, but I have no idea how much. In this particular case (4 ft embedment, 1" dia AISI 1018CR), the concrete had at least 28 days of cure (3,500 psi from Scmidt Hammer test). Since that time, I have seen plain bolts break under failure load, I have seen them develop the cone, and I have seen some pull out. On one structural failure in New Jersey all 3 modes were observed on identical designs. (A big warehouse blew over during construction.) My only conclusion from personal observations, and research is that bond strength on plain steel is too variable to rely on. And if you think that the anchor bolts are held in place by templates as the concrete is placed and consolidated around them, you need to get to a job site to watch them "floated" in after the concrete has taken an initial set. It makes the little hairs on the back of your neck stand up. Every engineer should become a special inspector for a while. Regards, Harold Sprague > -----Original Message----- > From: Mark Baker [SMTP:shake4bake(--nospam--at)earthlink.net] > Sent: Wednesday, October 25, 2000 12:41 AM > To: seaint(--nospam--at)seaint.org > Subject: Re: Embedded Anchor Bolts In Compression > > Hi Harold, > > I do not deny the validity of cone failure and its application to > designing > embedded anchors. But the fact remains that such an animal as bond does > exist. Yes, scale on a bolt, oil, rust, zinc, roughness (or lack there of) > etc. will impact the bond performance of an embedded bolt. And I am sure > those who came before us who relied upon bond were competent engineers > aware > of this fact who specified "clean and free of deleterious material". > > When faced with a problem, such as that in Bill's initial post, where the > numbers aren't working, I step out of my blissful little engineers world > and > ask myself "what else could be going on here that I am not accounting > for". > This point of view was the spirit in which my post was sent and I hope > that > is the way it was received. > > How green, by the way, was the concrete in which the bolt pulled out :0) > > Mark > > ----- Original Message ----- > From: Sprague, Harold O. <SpragueHO(--nospam--at)bv.com> > To: <seaint(--nospam--at)seaint.org> > Sent: Tuesday, October 24, 2000 9:42 AM > Subject: RE: Embedded Anchor Bolts In Compression > > > > Mark, > > > > The reason that bond for plain bars went out of fashion was due to the > > variability, and the potential for catastrophic failures. The original > bond > > strengths were predicated on very limited testing of hot rolled mild > steel > > which had a lot of porosity at the surface. Cold rolled shapes did not > have > > this surface porosity. More modern rolling mills had much less surface > > irregularities than older mills even for mild steel. Bond strength > testing > > to plain steel could not be validated. > > > > Personally I saw an iron worker back out an unheaded anchor bolt that > was > > embedded 4 feet into a drilled shaft. It backed out just due to the > tension > > from tightening with a plain spud wrench. According to ACI 318-63, the > > embedment was enough to fully develop the bolt. ACI 318-63 was the last > 318 > > that allowed for bond to plain steel. > > > > Regards, > > Harold Sprague > > > > > > > -----Original Message----- > > > From: Mark Baker [SMTP:shake4bake(--nospam--at)earthlink.net] > > > Sent: Monday, October 23, 2000 9:41 PM > > > To: seaint(--nospam--at)seaint.org > > > Subject: Re: Embedded Anchor Bolts In Compression > > > > > > Just because it is not in fashion anymore to design anchor bolt > embedment > > > based upon bond....... > > > > > > Look back at mid 60's vintage ACI manual for bond strengths at various > f'c > > > and bolt diameters. Let me know if you can't find it. > > > > > > Mark > > > > > > ----- Original Message ----- > > > From: Bill Polhemus <bpolhem(--nospam--at)swbell.net> > > > To: <seaint(--nospam--at)seaint.org> > > > Sent: Monday, October 23, 2000 3:26 PM > > > Subject: Embedded Anchor Bolts In Compression > > > > > > > > > > I know we talked a little about this a few months back, but now that > I > > > have a > > > > little more knowledge (a "little knowledge" being, of course, a > > > dangerous > > > thing) > > > > about the topic, I'd like to recast the question I asked before. > > > > > > > > In some instances there are advantages to NOT grouting structural > column > > > base > > > > plates. For example, our stated DOT does not allow grouting of > column > > > base > > > > plates for overhead traffic sign structures, which are typically > hollow > > > sections > > > > and have cables or conduit running up into them from the bottom (the > > > base > > > plates > > > > have concentric openings to allow this). They are afraid that > condensed > > > moisture > > > > will build up inside the columns and cause accelerated corrosion. > > > > > > > > Thus, no grout under the base plates, and the compression AND > tension > > > forces are > > > > carried by the anchor bolts, the plate resting on the levelling > nuts. > > > > > > > > An embedded anchor bolt in compression would tranfer the column > forces > > > into the > > > > concrete pedestal by bearing on the nut at the bottom of the bolt. > But > > > these > > > > forces are bound to be large, and using the ACI code-calculated > bearing > > > strength > > > > of the concrete under the nut (ACI 318-10.17.1) is not going to be > > > sufficient > > > > for such a force. > > > > > > > > Does anyone have any experience with this? What did you use to > determine > > > > adequacy? > > > > > > > > I seem to recall that research into anchor bolt failure mechanism > showed > > > that, > > > > because of localized confinement, the bearing at the nut allowed was > > > typically > > > > on the order of many times the ACI 318 code calculation, when the > bolt > > > is > > > in > > > > tension. Not sure if the same would apply here. > > > > > > > > Look forward to your input. > > > >
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