Round HSS Pile - Plastic Hinge Structural Capacity

[CarlosMo]

Dear all,

I have a question on my mind, I wonder if anyone can help me.

I am performing a structural evaluation in order to determine the structural capacity (using SAP2000) of an existing steel concrete cap structure supported by steel pipe piles (ASTM A36) when subjected to an abnormal horizontal displacement.

To evaluate it´s structural capacity I am performing a Nonlinear Time History Analysis using plastic hinges (SAP Automatic Fiber Hinge) but I am in doubt if I can follow the plastic hinge procedure due to width-to-thickness ratios (AISC Tables B4.1a and B4.1b).

Corroded Pile diameter and thickness are 0.505m and 0.008m respectively. Looking at AISC Table B4.1a, D/T (value=63.13) is less than 0.11 E/Fy (value=88). Being this I understand that I am dealing with a nonslender section and a plastic analysis could be performed.
But if I look at AISC Table B4.1b, I conclude that the same section is noncompact D/T > 0.07 E/Fy.

So my first question is, can I perform a Time History Analysis using plastic hinges on piles, knowing that they are subjected to compression and flexure and section is nonslender (compression) and noncompact (flexure)?

Second question: Is SAP2000 Automatic Fiber Hinge (P-M2-M3) the best feature to evaluate structural capacity for steel pipe piles?

Thanks for your help guys!

 

[dik]

To develop the plastic section, a tube/pipe has to maintain it's x-section... some pipes and tubes buckle locally prior to developing their full plastic strength.

Dik

 

[CarlosMo]

Hello dik, thanks a lot for your answer. I agree with your statement.

So regarding the pile case presented above, would you consider that a plastic analysis should not be performed?
In this case what should govern? The compression (being non slender) or flexure (being noncompact)?

Thanks

 

[dik]

I wouldn't normally use plastic design for that situation... I would think flexure would govern, but, you'd have to run the sums to verify it.

Dik

 

[CarlosMo]

Thanks a lot dik for your comments!!!!