Roof Diaphragm Openings

[TRAK.Structural]

See sketch below. A client of mine has asked to have a 2-story loft built inside of a pre-fab pre-engineered steel barn structure. Due to the barn structure being engineered for only its on weight and wind/seismic as applicable only for itself the loft would not be attached and completely independent of the barn. Ignoring the difficulty to build this and the general oddity of the situation (which I have informed him of) I am considering allowing some penetrations in the "roof" diaphragm to allow for greater heights in the loft. The openings would be required to allow the barn structure frames to pass through. The barn framing is at 4' OC so there would be quite a few of these over the 30' length of the loft. Lateral loads are minimal since this is inside an enclosed building, what do you all think of this idea?

 

[SWComposites]

why do you need a "roof" on the new loft structure at all? seems needlessly complicated and will hide the actual roof for maintenance.

why not just new posts and a floor system for the 2nd story area?

 

[KootK]

With openings that frequent:

1) Big hassle to frame around properly as a proper diaphragm opening.

2) Probably becomes more like a strip opening rather than discrete openings.

Perhaps you could rationalize the diaphragm as shown below with subdiaphragms, ignoring the rest.

At the ends, you'll need some chunk of something to be kind of like a wind girt. Shouldn't be too tough to resolve.

 

[TRAK.Structural]

why do you need a "roof" on the new loft structure at all? seems needlessly complicated and will hide the actual roof for maintenance.

why not just new posts and a floor system for the 2nd story area?

There are walls at the upper level so no one falls off and also to define the spaces in the loft. The "roof" will hold it all together and just makes it easy to use conventional load paths.

With openings that frequent:

1) Big hassle to frame around properly as a proper diaphragm opening.

2) Probably becomes more like a strip opening rather than discrete openings.

Perhaps you could rationalize the diaphragm as shown below with subdiaphragms, ignoring the rest.

At the ends, you'll need some chunk of something to be kind of like a wind girt. Shouldn't be too tough to resolve.

I think I can provide some amount of blocking around the openings and maybe extend it a rafter spacing or two if needed. I don't think any of the loads will be tough to resolve; more or less just doing a sanity check here.