CSI SAFE Columns reaction 1

[Gus14]

When modelling a simple story in CSI safe subject to uniform gravity loads only (Z-direction), I get columns reaction in the (X&Y directions). Why is that?

Sidenote, To determine the column moments, I usually assume the columns restraint is fixed at the top and the bottom similar to the subframe method used in beams.

 

[TLHS]

I've never used SAFE, but if your columns are fixed to your floor / beam system at height then there will be a moment transfered from the floor to the columns. If your column is pinned at the base, that moment resolves with equal and opposite lateral kickout forces on the columns. If it's fixed at the base, then some of it will be end moment and some of it kickout. If you don't think it's realistic for the amount of foundation restraint, then put rollers under all but one (or however many you need to restrain for stability given the number of degrees of freedom) and your frame will be free to deflect such that those forces don't develop. You'll have a higher deflection, though.

As a diagram from a random google search (I haven't read the page):

https://engineering.stackexchange.c...g-bending-moment-diagram-of-a-frame-structure

 

[Gus14]

Thank you THLS, for replying I looked at the diagram and see what you mean. I also ran the software and observed what you said.

If you don't think it's realistic for the amount of foundation restraint, then put rollers under all but one (or however many you need to restrain for stability given the number of degrees of freedom) and your frame will be free to deflect such that those forces don't develop. You'll have a higher deflection, though.

In flat slabs for example, If I do this do I need to account for the increase the deflection by increasing the slab thickness ?

 

[Gus14]

I built a study model of a flat slab where the reactions along x on one column was 50 KN, and another column reaction was 40 KN. My questions are :

1- Do I have to stick with these reactions, design those columns as shear walls and design the foundation to resist them? ( I mean if this happens for 5 floors that it becomes problematic dealing with the foundation design )

Or

2- Does releasing the column's ends and accounting for the increase in deflection by increasing the thickness prevent these large forces from developing? Or is assuming fixity not reasonable in the first place due to the large demand in lateral force resistance?

Update on my learning process to how I answered these questions :

1. some of the lateral reactions cancel out, the whole structure works as a frame. I don't need to bother myself with these lateral reactions, rather I need to pay attention to the reaction at the bottom of the frame. Modeling as a fix support is just an approximation of how the structure distribute the moments to the columns, and I should not release the columns moments in flat slabs.

However, I now don't trust the deflection software results with fixed columns. Maybe modeling is too ideal compared with real life.