Question about horizontal bracing in steel framing

[faromic80]

When designing steel floor framing, I'm looking on input on how others resolve floor framing lateral loads. for example, the wind load are uniform across the building, but are assumed to act at the joints. Do you design the diaphragm (metal decking, concrete on metal decking, or whatever it may be) to resist the lateral loads and reduce deflections, or do you provide horizontal cross bracing to take out the lateral loads? Or do you use both? I was just talking to a coworker about this.

 

[jike]

It depends.... I would first look at using the floors or roof as a diaphragm. If the floors or roof are incapable of acting as a diaphragm (too many holes, large loads, unusal configuration, etc.)then I might resort to horizontal bracing or adjust my lines of vertical bracing to make the diaphragm work.

 

[faromic80]

I've seen horizontal cross bracing in all the perimeter bays of a floor framing scheme before. Could you design the bracing and not take into account the diaphragm to be conservative? or is that over conservative?

 

[JrStructuralEng]

Faromic,
For joists running perpendicular to wall:
- Horizontal bracing MAY not be required as each joist transfers load from the wall directly into the floor diaphram. Some bracing MAY be required so the joists can handle the axial load near the permiter. You could specify the axial load on the drawings per joist and let the joist designer/supplier determine the bracing requirements.

For joists running parallel to wall:
- Use horizontal bracing to transfer load into first couple joists to allow for distribution of the load into the floor diaphram. The amount of load will dictate how many bays are braced and the spacing.

Of course the above depends on your wall-floor detail (i.e. how the walls tie into the floor system) But typically this would be the case. I've seen building envelopes where no horizontal bracing is included in the floor system.