Diaphragm with Angles 3

[Lion06]

I've never actually had to design a diaphragm that consisted of angles in the plane of the roof, but I'd like to read up on it. I always thought it would be fairly easy to do, but the more I think about it............... I'm not so sure.

Well, the angle design wouldn't be difficult, but integrating it into your modeling seems like it could be.

Does anyone have any information or papers on this? I tried searching the site and came up empty, and I didn't have any luck doing a google search, either.

 

[ishvaaag]

If I understand your exposition well, it is just a matter of laying the member as any other in the model.

Maybe you refer to the difficulties I more than once have referred in this forum to place the members at the proper insertion points and with proper constraints, even asking for an inexistent handbook on the matter.

Since you are not getting out of planes of the building envelope, you get the most of it when every plane of the box is braced. You skip your roof and wall holes, and that's all.

 

[hokie66]

Do you mean instead of using a diaphragm, discrete members are used to brace the roof plane? If so, the design is just like any other truss. In Australia, diaphragms (except for concrete slabs) are not used extensively. We tend to use metal roofing for watertightness, but do not depend on diaphragm action of the roofing. Members used in the roof bracing include angles, circular hollow sections, and rectangular hollow sections. Sometimes even wide flange sections.

 

[msquared48]

Yep. Just load the horizontal truss and analyze it normally.

Mike McCann
MMC Engineering

 

[hokie66]

One other thing...don't forget to allow for the self weight bending/deflection of the members.

 

[Lion06]

I should probably clarify my question.

I understand how to do the design. My question is how do you get the load into the flat truss to begin with? Wind is pretty straightfoward - the edge member is the loaded edge of the truss. Seismic doesn't seem as clear to me since the load isn't being delivered from the facade, but rather from wherever the mass happens to reside.

 

[hokie66]

Some of the load is being delivered from the facades, so is applied at the perimeter. The other load is from the roof itself, and you can apply that at the panel points of the truss.

 

[Lion06]

Ok, that seems reasonable. This seems like it would not be very easy to incorporate into a model that determines and applies the location of the lateral loading, such as RAM Structural System.

 

[slickdeals]

A good article from Modern Steel is here