Anchor bolts with no hook or bolted end-Concrete cone? 7

[IJR]

Pals

There are some cases where loading is very small and a nominal bolt size would be OK for even tension. Straight rods come handy then-being easier to fabricate in large number.

Literature discourages use of straight rods for tension and stops there without providing any strength analysis

Will such a rod develop a concrete cone? I mean can I go along and treat it as bolted with no bolt projection?

Or is there any reference text you can suggest?

respects
IJR

 

[WillisV]

I'm not sure what literature you are referring to but generally it is the opposite - literature discourages the use of hooks in tension situations as they tend to straighten out and cruss the concrete locally at the bend. Use straight anchor rods with a hex nut threaded on the end.

 

[JKW05]

I thought I saw an old reference (maybe an old PCI manual)that would permit this if the bond strength could be determined for the length of the anchor. Having said that, please refer to ACI Appendix D:

"Cast-in anchor - A headed bolt, a headed stud, or a hooked bolt installed before placing concrete."

As Willis notes, hooked anchors are discouraged for tension applications. AISC specifies that "hooked anchor rods should be used only for axially loaded compression members subject to compression only and prevent the displacement or overturning of columns due to erection loads...."

I would just add the nut. They're not that expensive.

 

[IJR]

Thanks pals

But can you help me on how to design a straight anchor?Can a straight anchor develop a cone the way a bolted anchor does?I dont want to use a bolt at the end of the rod.


respects
IJR

 

[WillisV]

IJR - ACI Appendix D is the state of the art for anchor rod calculations. One of the limit states is pullout of the anchor rod, and the pullout limit state is based on the bearing area of the head/nut/washer at the end of the bolt. Therefore with a straight bolt that has no bearing area the pullout value would be zero by this method.

Not to say that there won't be bond etc. developed - you just can't count on it. Personally I would not use a straight, non-deformed, non headed or nutted anchor rod to resist tension.

 

[Lion06]

I agree with WillisV. Don't ever count on a straight bar with no head or nut welded to the end for any kind of tensile load. You may get some bond from the concrete, but nothing you can hang your hat on.

 

[IFRs]

If your anchor is an epoxied into the hole, consult with the likes of Hilti to find the capabilities of an idealized bolt.

 

[sdz]

You can make straight anchor bolts by threading the end of reinforcing bar. You won't get a breakout cone type failure but you can design anchorage using the normal development length rules for reinforcing.

 

[Taro]

sdz, do you know of a technical reference for development of threaded rods in concrete? I have never seen research that indicates the development lengths for rebar also apply for threaded rods.

 

[sdz]

Taro, No I don't. I'm talking about threading one end and leaving the embeded end as reinforcing bar.

 

[IJR]

Sdz, Taro

If you design such a rod using ACI bond lengths or similar , you end up with a flag post while Hilti and the like show up with their short magic wands.

Really a theory will help.

respects
IJR

 

[oldrunner]

IJR:

To your original post: No, you can't develop a cone with a "straight" rod because there is no horizontal surface of the "head" or a "nut" to bear against the concrete. That's why there is no strength analysis.

In Chapter 13 of the 1963 ACI Code for buildings, there are formulas for computing the bond stress for deformed bars. The code also mentions that smooth bars have to be twice as long as required for deformed bars.

For epoxied-in bars, I believe most ICBO reports require special inspection. Check with Simpson Strong-Ties latest catalog and their Titen HD's. I believe that you can add install these anchors that will take a tension load.

I personally would not use straight bars for any tension loads.

 

[DRC1]

If the rod is disturbed while the concrete is somewhat plastic or if the concrete, when it cures shrinks slightly, from the rod, the rod will have very little capacity. Should neither of these occur, concrete/ steel bond is not highly predictable and depends on many factors, not the least of which is the surface condition of the rods. Further when pouring the concrete and the bolts, it is best to have a top (out of pour) and bottom(in pour) template. The bottom template, connecting all the bolts in a pattern will also provide significant pull out resistance.

 

[saajr]

I saw that in Feb. 2007, sdz was looking for a paper entitled "Slip Pullout Strength of Hooked Anchors" by D. Kuhn and F. Shaikh. Does anyone have a copy available? I have done a fairly exhuastive search and haven't found it yet. Any help is appreciated.