Effect of area spring at slab on column

[dccd]

Say that a simple building is supported by 4 columns , the column sitting on base slab. I assigned some sort of area spring to the base slab. When the area spring assigned is higher, this cause the compression of the column to be higher. I have 2 models, one showing the bending at beam/column junction is higher, another showing the bending moment at beam/column junction is lower. Which is correct? I am confused.

I think the hogging moment at beam/column junction shall be lower when the area spring at base slab is higher. This is because when the area spring is higher, compression on column is higher, this caused the column to be weaker, because of elastic shortening of column, higher compression force on column, column shorten more, the column is weaker. Hence, when column is weaker, it’s not able to support higher hogging moment at the beam-column junction.
Correct me if I am wrong.

 

[hetgen]

I think you have to use a range figure for the soil subgrade modulus (area spring) and design for the envelope. check this thread

 

[dccd]

Thanks , the thread seems didn't show the effect of spring on moment of beam-column junection

 

[hetgen]

What do you mean by 'the column sitting on base slab'? is the column supported on mat foundation?

 

[dccd]

Yes, dont bother about the wording, the column is sitting on the mat , mat is supported by spring