Flexible Diaphragm analysis with Nonparallel Irregularity

[jwags]

I have a trapezoidal building with a wood roof. I am trying to analyze the roof diaphragm but don't really know how to do a flexible diaphragm analysis with the one skewed wall. Three walls form a C-shape and intersect at 90 deg. The fourth wall is at an angle of 125 deg from one wall and 55 from the other. If I consider two orthogonal directions, this will result in out of plane forces developing on the skewed wall. Should one consider the diaphragm as rigid for distribution of lateral forces or is there a better analysis procedure because I know the walls will not be able to handle the out of plane forces? Does any one know of any good refernece material that would help me resolve this issue? Thank you in advance for any assistance.

 

[frv]

It may help if you post a sketch.

 

[jwags]

frv - I have attached a quick sketch. The walls are plain masonry walls 12" thick and are 22' tall.

 

[JLNJ]

It seems to me that your diaphragm will have to resolve some cross forces when loaded in the long direction. My guess looking at you aspect ratio is that it shouldn't be a problem. Interesting.

 

[JoshPlumSE]

Even if you design the diaphragm as a "rigid diaphragm" you still have to reinforce the area around the opening to transfer the forces that it will experience.

Though, I don't know of a good method (short of FEM modeling) to come up with a good estimation of the strap and chord forces. At least not for something so irregular and non-orthogonal.

 

[asixth]

What creates the diaphram? Roof sheeting, plasterboard sheeting and how is that force being transferred into the internal walls and at what spacing are the internal walls.

I see that as a building with walls on four sides. The fact that 3 walls are orthogonal to each other and the other has resultant vectors of 0.823 and 0.567 (by my calculations) shouldn't have a significant bearing on the distribution of forces to the walls.

If you model the building with 4 walls each with a component of reaction and model side wall pressures, the torsional moment produced by the building will be insignificant (IMO).