Threaded Rod - App. D or Rebar? 1

[Lion06]

What is everyone's opinion on threaded rods regarding the benefit of the threads in developing the rod?

In my mind, this is what App. D was made for. How often do you see an achor rod with a nut that has no threads? If you can say the threads make it as good (or even some reliable factor smaller) than rebar, then App. D has little application.

While I believe that the threads do help the rod bond to the concrete better than a plain bar, I don't believe that it is reliable and shouldn't be counted on in design.

 

[frv]

Nothing more than an educated guess, but I agree with you.

 

[DaveAtkins]

I don't think anyone counts on the threads to develop the rod. You must either have a nut and washer at the embedded end (this is preferred) or a hook.

DaveAtkins

 

[miecz]

In order to take advantage of the threads contribution to bond, someone would have to perform tests comparing threaded rods to plain, and then publish the results, and so on. I don't know if that has ever been done. Sounds like useful research material to me, compared to some of the heady stuff that's published in ACI's Engineering Journal. Too pedestrian, I guess.

 

[slickdeals]

I think appendix D is really intended for a failure for headed studs where a cone is developed from the base of the head propagating upward.

I agree with you that rebar and threaded bar need not necessarily be treated differently.

Check the following paper that I got from Hilti regarding bond strength for epoxy anchors. Hope this will help.

 

[TXStructural]

The deformations on rebar are tested to provide development. Rebar deformations are specified in ASTM A615 and A706, are very specific, involving spacing, depth, and width. The threads on a piece of all-thread are too shallow and too close together to effectively engage the concrete without an adhesive (as for post-installed anchorages.) Small machine threads will easily pull out of concrete.

Threaded bar made to A615 dimensions (such as those from SAS or Dywidag) meets the deformation requirements needed to use ACI development length calculations. These are sometimes used as anchors for very large equipment.

The intent behind headed anchor rods is that the bond all occurs at the head. It is not uncommon to apply a bond-breaker to the shaft of the anchor rod, particularly if the anchor is to be pretensioned, where bond along the rod would interfere with effective pretensioning forces. The length of unbonded rod/bar is stretched in the pretensioning process, acting as a very stiff spring to retain the tension on the anchor, as might be required for normal thermal changes.



John Turner CSP PE
CRSI Greater Southwestern Regional Manager

 

[LSPSCAT]

You can find information from Williams regarding grout bonded anchors. (Hollow core, threaded, plain bar and headed bar) Everything is out of date based on todays codes and Williams publications are still based on ACI 349 for nuclear work. However, last time I called Williams they stated that this was still applicable to testing they had been involved in.