Roof horizontal bracing between frames

[palk7 EIT]

Hi,

If we consider the roof metal deck or roof CLT panels as the diaphragm and they are going to transfer the lateral forces to the perimeter beams and then the perimeter beams subsequently transfer those loads to the Vertical lateral force system, then in this case it is not necessary to provide a roof horizontal bracing right? If so what is the case when a Roof horizontal bracing bracing between the frames is needed? if I provide roof horizontal bracing then I don't need to consider the roof metal deck or roof CLT panels as a diaphragm ?...... Highly appreciate your input and also happy to read about it if anyone could share a resource with regards to understanding the basic diaphragm to vertical lateral force resisting system.

Thank you

 

[kostast88]

Eurocode does set some rules on your diaphragm, see: EN 1993-1-3 10.3 "Stressed skin design". They say what it can and can't do, specifying under which conditions. Fastener spacing is one, and a few others.

In my experience it depends on how much faith you have on your roof metal deck. This usually comes down on what your dimensions/opennings are.

 

[KootK]

Sheathed diaphragms and discretely braced diaphragms basically do the same job. I echo kostast88's thoughts on it having much to do with how much confidence you have in the diaphragm to do it's job. In North America it is pretty common to use the sheathing as the diaphragm. Some situations where discrete bracing is used include:

1) Pre-engineered buildings using standing seam roofing that doesn't have great shear capacity.

2) Large scale, long span structures like stadiums and conference centers where sometimes the scale of the thing get to be too much for it to be braced by sheathing.

3) Some industrial structures where, as far as I can tell, the designers simply do not like to mess around with minimal/marginal structure.