Attributes of a braced column

[GreatExpectations]

I'm doing some simple preliminary work on a 3 storey building. I understand that a braced column is one that has lateral loads resisted and sidesway resisted i.e. by diaphragms.

My question is that do we need to design the slabs and beams such that all columns are constrained to move equally in the lateral direction. I know that we do not need to restrain the columns against rotation

Looking forward to your insights

 

[ishvaaag]

I don't understand very well the question, but if the issue is to prevent the amount of deflection in every orthogonal direction under some set of loadcases, it is a matter of adding stiffnes to the purpose in the lateral resisting system. Such stiffness may be provided by braces, walls, moment resistent frames or other means. You may also want to restrict the relative displacement at the floors or roofs and if not rigid enough by themselves it may involve some additional bracing system at floor or roof levels, or changing the floors and roofs to such more rigid solutions.

From the technical viewpoint, typical braces are just line elements endowed with all their structural properties. That some program may elect to restrict their behaviour/input data to fit some particular structural/input/outout/structural intent is just another entirely different matter, and we would need to examine the particulars of what for such program a brace is.

 

[Lion06]

I don't quite understand your question. Slabs and gravity beams have very little to do with how much the building drifts. The lateral stiffness of the building comes from the lateral system (e.g. braced frames, shearwalls, moment frames). Additionally, it is impossible of have every point on a floor move laterally the exact same amount. This can only be done with zero torsion on the building. It is highly unlikely that this will occur in ANY load case, and completely IMPOSSIBLE that this will occur in every load case.

This seems like a very fundamental question that you should be talking with a senior engineer at your company about.

 

[BAretired]

My question is that do we need to design the slabs and beams such that all columns are constrained to move equally in the lateral direction.

No, but all columns which are attached to a particular floor or roof slab will be automatically constrained to move equally in the lateral direction.

BA

 

[BAretired]

I should add "unless the floor rotates torsionally".

BA

 

[JAE]

...or if it is a flexible diaphragm.

 

[BAretired]

JAE,
Are concrete slabs ever considered flexible diaphragms?

BA

 

[JAE]

BA - I think sometimes they actually do if they are large enough and flexible enough under the code - I think there are definitions out there for flexible diaphragms that might apply.

I was just adding the flexible diaphragm (despite the "slab" term) as a case where columns lateral movement would vary from column to column.

But in general you and I and my dog all assume a concrete slab is rigid.

 

[BAretired]

JAE,
Didn't know you had a dog, but I'm pleased to hear that the three of us agree.

BA