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High Cycle/Fatigue Loading of embedded Concrete Anchors

High Cycle/Fatigue Loading of embedded Concrete Anchors

High Cycle/Fatigue Loading of embedded Concrete Anchors

(OP)
If you'll note, this thread is marked as a tip (rather than a question). But any questions/comments are welcome.

Some years back, I asked the question on here if anyone had some guidance on steel (headed) anchor bolts embedded in concrete subjected to fatigue loading. (Primarily focusing on the concrete aspect.) Since then, I've done some research and found some info that I'd thought I'd share. It's kind of a survey of the available literature on the subject (that I am aware of).

This table is sort of a summary of the endurance limits:




References:

[1] 'Static and Dynamic long-term behavior of anchors', by: Walter Ammann, Paper SP 130-8 (in SP-130), ACI (1991)

[2] 'Headed studs close to the concrete surface-fatigue behavior and Application', by: Kuhlmann, et al. International Conference on Composite Construction in Steel and Concrete (2008).

[3] 'Anchorage in Concrete Construction', by: Eligehausen, et al. Ernst & Sohn (2006), p.139-142, 162.

Notes:

[A] This testing involved a Hilti expansion anchor. This reference also notes that losses in pre-tensioning the bolt will typically be about 30-50%.

[B] This testing involved headed studs loaded towards a free edge. Perpendicular to a free edge, AASHTO's requirements should suffice.

[C] In this reference it says (in the uncracked concrete section): “It is therefore to be expected that the fatigue strength associated with concrete cone failure is at least equal to the fatigue strength of concrete subjected to uni-axial tension. This premise was confirmed in tests with single headed studs and groups with four studs.....” This would mean it would be analogous to tensile failure in ACI 215R-74. (The latest addition I have.) ACI 215 has several charts that deal with fatigue strength in tension.

[D] For cracked concrete, this reference says more research is needed.

Discussion:

One thing about all the testing info I saw in all of these references is: the testing was limited to about 2-10 million cycles. (Typical for fatigue testing.) But ACI 215 has this reminder that you aren't dealing with steel: “It may be observed that the S-N curves for concrete are approximately linear between [100 and 10 million] cycles. This indicates that concrete does not exhibit an endurance limit up to 10 million cycles. In other words, there is no limiting value of stress below which the fatigue life will be infinite.”

And that is especially significant if you are doing anchors for machines. Given that, my habit of always placing a re-bar in the failure zone (to act as tensile reinforcement) in such a situation (and always using the pretension to transmit the shear)....helps me sleep a little better.

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