Lateral Stability for a Steel Structure

tristan861 · Dec 28, 2020

Hello Guys

I have this steel structure plan view as the sketch shows. How do I handle with the lateral stability in this case?
As shown, in X direction most of the frames are supported by an existing concrete slab or shear wall. In Y direction some of members are supported by the shear wall.
Can I release the moment in all beams and consider this structure laterally stable without adding v.brace or making moment frames?
Or should I deal with each frame separately and change the beam to column connection to a moment connection where it is not supported on a rigid element?

Note: Base plates are pinned connected for all steel columns.

dik · Dec 28, 2020

Can you use masonry in-filled walls?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

tristan861 · Dec 28, 2020

No.
It is an open structure.

MegaStructures · Dec 28, 2020

I don't see why you wouldn't be able to count on the shear wall if:

a) The horizontal bracing is sufficient to transfer the lateral forces from the unbraced side to the shear wall
b) The shear wall is sufficiently strong to support the full lateral force on the structure

If it were me I would just brace both sides. I take it you aren't using a matrix structural analysis type program to design this structure?

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”

MIStructE_IRE · Dec 28, 2020

Surely your diaphragm floor plate ties back to that very stiff looking lift shaft?

r13 · Dec 28, 2020

No. It is an open structure.

Then, wouldn't it be considered as a "lean to" structure, which relies on the stiffness of the supporting structure to its right. I would say "yes, it is possible".

tristan861 · Dec 28, 2020

Yes, its a lift shaft.
r13; Im not sure I understand what you mean by "it is possible"

MegaStructures · Dec 28, 2020

Of course it is possible, the challenge at hand is to prove it. Is there a reason you don't want to add bracing in the y-axis opposite of the shear wall?

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”

r13 · Dec 28, 2020

We don't have a complete picture/knowledge on the structures, its use, and type of loadings it subjects to. For instance, the supporting structure is quite flexible, and wind or seismic load is likely control the design.... MegaStructures said better then.

HTURKAK · Dec 28, 2020

Yes it is possible.. provided that the floor deck ( composite deck?) will serve the diaphgram action for lateral stability. The connection of deck to the lift shaft and shear wall shall be detailed to transfer the horizontal loads..

MegaStructures · Dec 28, 2020

Tristan how are you analyzing the structure? It sounds like you might be doing this by 2d frame analysis? I would really want to use a 3d analysis procedure to verify that it's ok to have asymmetric bracing.

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”

tristan861 · Dec 28, 2020

HTURKAK

Unfortunately, the deck is not composite and no adequate space for H. brace due to the required openings.

MegaStructures
Im using 3D analysis using FEM.

I decided to not count on the shear wall alone. As you can see, multiple systems might be there (braced and moment frames).
I forgot to mention that the structure is around 65 ft height consisting of 5 floors similar to this one.

Should I worry about the asymmetrical bracing? would it induce additional torsion/ eccentricity on the building for example?

Here is the plan view again. I really would like to know your opinions.
Thanks alot,,

r13 · Dec 28, 2020

Should I worry about the asymmetrical bracing?

Yes, unless the floor is non-rigid.

human909 · Dec 28, 2020

Like many of these questions there just isn't enough detail to give an answer.

Of course the left side need to be laterally restrained. Either braced in elevation, braced in plan to restrain it on the shear wall or moment framed. The best course of action depends on the needs of the structure. Moment framed could give you issues with differential deflection compared to the stiff shear wall.

I am puzzled by the existing in plan cross bracing. It seems a bit arbitrary. But of course I only have 10% of the picture so there might be some good reasons for that approach.

r13 · Dec 28, 2020

I think the X indicates void/open space.

KootK · Dec 29, 2020

op said:
How do I handle with the lateral stability in this case?

I've made a lot of assumptions here but this is how I might approach your situation. I sense that this is an industrial structure which often means:

1) You definitely want competent stability bracing and;

2) Diaphragms are often ineffective and/or non-continuous so some concessions to pragmatism must be made.

Obviously, adding in some more bracing is only going to improve stability and, perhaps, constructability. What I've show for bracing below is my practical minimum.

KootK · Dec 29, 2020

At the other end of the spectrum, you could spend a few extra bucks to do something like this and then be almost independent of diaphragm action, both during erection and in service.

tristan861 · Dec 30, 2020

KootK

Thanks. [smile]

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