P-Delta in service loads

[ingdaniel]

I all,

I have a question about P-delta analysis.

I am doing a explicit second-order analysis in a steel structure (LRFD), and according AISC Design Guide 28, when performing a second-order analysis, the analysis must be conducted at the ultimate load level.

OK, I have to do it for every combination (i.g. 1.2DL +1.6LL).

But my question is for foundation design, soil capacity, overturning and sliding, i need service loads no ultimate loads.

In this case what can i do to have service loads including second-order loads?

Hope you can help me

Best regards,

 

[TehMightyEngineer]

I wouldn't think P-delta effects would impact the soil capacity or overturning/sliding loads.

Maine EIT, Civil/Structural.

 

[ingdaniel]

P-delta effects will increase the moment at the base (fixed base).

 

[TehMightyEngineer]

Perhaps you could get the forces similar to how the direct analysis method can be used in ASD.

Factor your load for the load case and compare it to the unfactored equivalent load case. You should then be able to figure out a combined, overall factor by dividing the factored load by the unfactored load. Run your P-delta analysis using the factored loads and then divide your final elastic + p-delta combined load by the overall factor you figured earlier.

This should result in a unfactored load case that used the factored loads for the P-delta analysis.

Maine EIT, Civil/Structural.