Pipe Column Transition 3

[aggman]

I have been working through the design on a single pipe column fixed at the base to a circular concrete pier. The column is 42" in diameter. I am having some trouble with the anchorage with regards to concrete bursting on the anchor head. This is being controlled by tighter than normal anchor bolt spacing. I am locked in with the 42" column because of an attachment up above requires that geometry. In an effort to improve the situation (going to larger and less anchors is not helping the situation enough and I like the redundancy of the multiple anchors) I would like to step the column diameter out to 54". Does anyone know of a design guideline or standard that covers steps in pipe columns subject to axial load, moments, and shear? I am trying to steer clear of a conical transition due to fabrication issues and lack of confidence with this having a good fit up when finished. Loads are being introduced by a slewing bearing roughly 60" above the base plate connection so we don't have a ton of room to make it all happen.

On another related issue, I can satisfy the bursting requirements if we use a template ring. If we account for a 10 degree wedge (the anchors are 1 3/4" on 10 degree increments) for the bearing plate (about a 5" segment) we can get sufficient bearing area to fully develop the 1 3/4" A-36 anchor. What are people's thoughts on a roughly 5"x6" bearing plate being stiff enough? I am basing the design criteria on ca1 being limited by anchor bolt spacing/2 as recommended in some research I have dug up on anchor bolt design into caisson foundations?

Thanks in advance for any thoughts.

 

[structSU10]

have you tried designing reinforcement to eliminate the failure modes from App. D?

See the paper in the link - you can get away form limits due to breakout and sideface blowout, which may be enough to get it to work.

http://www.google.com/url?sa=t&rct=...E9ZUNe714nUDiAiAw&sig2=43WvE8OfbjVBoQSLcgyLcA

 

[JStephen]

If you did use a conical transition, you might be looking for the "design guideline or standard that covers conical transitions in pipe columns subject to axial load, moments, and shear", so it doesn't necessarily solve all the problems.

I've seen the steps on big billboard and sign posts, but have no idea what design or detailing went into them.

Maybe a stupid idea, but can you put a boiler-type manhole in that column and then put anchors both inside and outside?

 

[aggman]

Thank you for the link strutSU10. That's more or less where I am in my head at this point. I'm settling in on a ring to locate the 36 anchors (has to be a factor of (9) because of the upper ring connecting to the slewing bearing uses 45 bolts and I need stiffening gussets to line up). The ring will be set using top and bottom nuts and hardened washers. I am leaning towards 1 1/2" plate which meats the stress requirements just not sure about stiffness needs. This concept technically meets the requirements to prevent the bursting failure. I'm just not totally happy that I believe it's good enough because of some of the research I have done. So as a backup I'm going to wrap the anchors with the ties that will hold 25% of the anchor tensile capacity. Just for reference I don't have to have the full yielding capacity of the anchor, but I want to design for it. My factored bolt tension is 56.508 kips and the 1 3/4" rod is good for 82.65 kips.

 

[KootK]

If the only issue is blowout at the anchor head, consider switching to something like Dywidag thread bar and just work out a non-contact lap system to the pier . Your embeddment depth will increase a bit but that's a pretty small price to pay to avoid all of the other potential complexity.

It sounds as though you've moved past the pipe transition business. If not, this book has a version of the sign structure column stepping detail that JStephen may have been alluding to: Link. I have a copy at home. If you're still interested, let me know and I'll scan it for you.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[aggman]

KootK, I would be interested in what it has on the transition analysis. I have sorta moved on from it for the moment, but I still have to resolve the base plate design.

In regards to the anchors, have you ever looked at the thread bars in fatigue? I've got some low cycle fatigue, which is partially controlling the anchor bolt design and I'm limiting the stress to 7ksi for a the total range. Fairly decent little problem to address all this stuff!