Bracing for moment frame

[imsengr]

Dear all,

I am working on a multi-story frame constructed with hollow structural steel. The client's preference for this is due to hygenice reasons and all my connections are welded moment connections. I have some horizontal tubes for my structure. I am wondering whether additional bracing in terms of X- or diagonal bracing on the horizontal platforms would be beneficial. I do not have any vertical bracing at all due to the constraints of equipment and access. Any advice?

Thanks.

 

[JAE]

Is this in a high seismic zone? I'm not sure if there are many (if any) approved moment connections between tubes for high seismic.

 

[imsengr]

Here are the 2% PE in 50 year

The 0.2 sec Spectral Response Acceleration is 32.05

The 1.0 sec Spectral Response Acceleration is
12.06

 

[ironmon]

I'm working on the same problem, client like tubes. Im my case I talked them into bracing.
For your case, Horizontal bracing only helps if you have a vertical stability system (vert bracing, moment frames, shear walls) in place to transfer lateral load to ground.

From what you wrote, sounds like you will need to use moment (rigid) frames. This will likely drive up your column sizes to twice what they are now, due to K (effective length factor) and seismic loads are higher for moment frames due to lower R (response) number.

Sometimes the big columns and expensive moment connections will have your client make adjustments and use the "KING OF VERTICAL STABILITY".......X-BRACING>

Ball park loads (guess) will be around 15-20% of mass form moment frame. Please verify that with code.

hope that helps.

 

[civilperson]

Diagonals in both vertical planes are the simple solution to lateral load with any shape steel system. Moment connections and induced bending in the columns/beams is high cost in terms of engineering, materials and rigidity.
Diagonals in the horizontal plane are usually redundant to floors/roofs/slabs.