P-delta effect for steel structure

[burtonSTR]

What percentage the p-delta contribute to stress ratio
for column of steel structure you found?

I got 1% for braced frame and 5% for moment resistent frame.

 

[enginerding]

A good estimate would be the B1-B2 multipliers in AISC. There is not a set percentage. If there were, it would be put in the code and we could avoid the detailed analysis.

 

[burtonSTR]

To enginering?

I see.

Just want to know a common situation. For example, one would like to control KL/r around 90-150 for column.

p-delta effect was some thing we can control by change the
rigidity of structure, as I understand. Similar as KL/r, I think it may have a allowance value.

 

[enginerding]

I usually look more to the total deflection (or drift) than to the amount of the p-delta increase in moment. I have done water towers where the p-delta effect with seismic has added over 50% to the design moment.

I don't know off-hand what it would usually be for buildings. I don't really consider them without p-delta to know the difference. It would be proportional to the gravity load and the drift - both of which can vary from job to job.

 

[csd72]

I have had around the 40% mark before under normal live and wind loads.

It really depends on how slender the structure is.

I expect that your code would give you a maximum allowable before you have to do an advanced analysis.

 

[JoshPlumSE]

I'd estimate that a total amplification of about 5 to 10% is common for building type structures. But, that is just a ball park number for those of us in seismic country.

This can increase if there are very few moment frames with a lot of "leaning" columns that don't participate in resisting the lateral forces.... more common for structures where the lateral design is entirely controlled by wind.