Appendix D for Round Piers

[JAX91]

Does anybody have a good design method for utilizing Appendix D on round piers? I am mainly looking for what to use for edge distances (camin, camax, ca1, ca2). I also need to figure out how to calculate effective embedment and and effective edge distance for ca1. Effective embedment comes into play when you are near three or more edges. How do you calculate the number of edges for a round shape? I considered just using the largest square that would fit inside the circle, but it is way too conservative, and my pier will have to get extremely large.

 

[DST148]

I am not familiar with Appendix D but a similar question was raised in another structural engineering forum. One of the references given was ASCE manual and report on engineering practice titled "Substation Design Guide" - It is for circular section with rod anchors. Also reference was made to

http://www.bechtel.com/assets/files/techpapers/design-of-anchor-reinforcement.pdf

 

[charliealphabravo]

It has been a while but I seem to recall that Hilti has a free software program that designs anchorage for round piers per Appendix D. It is mostly for their proprietary anchors but it might give you an idea how they apply these provisions.

I wrote a spreadsheet to implement Appendix D when it first came out and had the same questions. I believe the issues you are facing are usually resolved by using stirrups to contain the vertical bars or a welded base plate so that the concrete failure modes do not govern.

 

[JLNJ]

I asked Hilti this very question and Profis has no provisions for a round pier. The real question become what to use for the edge distance. I find that the straight distance normal to the pier edge is not conservative.

 

[charliealphabravo]

Thanks JLNJ for the correction on Profis.

The early versions of Appendix D did not rigorously consider the effect of transverse reinforcement. The theory is based on anchor rods in plain concrete and the influence of edges. I don't see much in the 05 version either except for minor coefficient adjustment when "supplemental" reinforcement is provided.

Appendix D is a very good tool but if you want to create anything remotely practical or slick like the round sign piers you see along the highway you will also need to formally consider stirrups and welded plates.

 

[TLHS]

They added to the instructions regarding allowance of supplemental reinforcement in the 2008 version of ACI 318. Look up "Anchor Reinforcement." It's pretty much a necessary part of developing pedestals or other small footprint anchor scenarios.

Basically, the goal is to develop reinforcement inside the failure cone and extend it into the main structure (using strut and tie if necessary) in such a way that if the cone tries to break out the rebar anchors the cone into the structure.

This is the method that should be used for any significant uplift loads or for any small footprint situations, such as pedestals or small footings.

 

[JLNJ]

Earlier this year I was struggling with round pier edge distance issues. Snapped this pic while up in the Wisconsin Dells this summer.

 

[JLNJ]

Sorry about that. Here's the link.

This supported a gigantic single stanchion cantilevered billboard. I was a bit nervous parking under it!

 

[JAX91]

TLHS...I agree with your statement that supplementary reinforcement will likely be required, but the actual edge distances, the effective embedment, and the effective edge distance are still needed to locate the breakout cone. The cone must be located to make sure the supplementary reinforcement is fully developed on both sides of it. Again, if I assume the largest square that will fit inside the circle, I could not rely on any of the perimeter vertical reinforcement to act as supplementary reinforcement.

 

[JLNJ]

Here's what I settled upon for the equivalent edge distance using the 35 degrees from Appendix D.

 

[charliealphabravo]

I'm guessing you've already seen this...a report for the retrofit of FDOT sign anchorage that incorporates Appendix D analysis.

http://www.dot.state.fl.us/research-center/Completed_Proj/Summary_STR/FDOT_BD545_54_rpt.pdf

 

[charliealphabravo]

and also this...a paper discussing use of the Strut & Tie Model (STM) for pedestals and the limitations of Appendix D.

http://www.bechtel.com/assets/files/TechPapers/design-of-anchor-reinforcement.pdf

 

[Lion06]

Make the anchors long enough to develop the pier reinforcing above the failure plane of the breakout cone and call it a day.

 

[GSigma]

Totally agree with Lion06. Just make sure the re-bar was designed for that load.