short column effect 1

[Groszni]

hello engtips, im designing a 4 stories rc structure, the lowest level height is 3.9m and the rest above are 4.2m. does the lowest column tend to have the short column effect? what are some thing needs to be check?

 

[BAretired]

I don't believe there is any special consideration for the "short column effect", whatever that means. Just design the columns in accordance with normal practice.

BA

 

[Trenno]

Are you talking about this kind of 'short column' failure?

 

[KootK]

Your column heights seem fairly well balanced from floor to floor really. Better than most buildings. I don`t think that you`ll end up with badly concentrated seismic forces at the main floor here.

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.

 

[Groszni]

@Baretired it said be occurs when you have a shorter column than the other level beacuse of the stiffness of its level differ (the more short the more stiff)

@trenno yeah kind of but this topic special to the height difference between the story

@kootk what kinda checking i should do? interstory drift? do i just design the column as the usual procedure of the column but probably with a bigger shear force and bending moment ?

 

[KootK]

do i just design the column as the usual procedure of the column but probably with a bigger shear force and bending moment ?

Just normal checking with whatever load effects are coming out of your analysis. Your short columns are still 80% as long as your long columns. You don't have a short column issue here in my opinion unless you are dealing with non-gapped infills like in Trenno's pics.

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.

 

[Shu Jiang PEng SE]

Take a portal frame with rigid connecting beam as example illustrate "short column effect". Assume the two columns have same cross section and a horizontal force is applied to the connecting beam. The horizontal displacement of the top end of the column is same due to the rigidity of the connecting beam. The horizontal force will be shared evenly by the two columns if the length of the two columns is same. otherwise, the short column will take more horizontal force. The reason is that: the stiffness of the short column is larger than that of the tall column and the two columns have same horizontal movement.