Roof Diaphragm Action 1

[AmirZamanian]

Diaphragm actions in a roof

A typical horizontal diaphragm can have an allowable shear value. Let’s take a hypothetical horizontal diaphragm in service under following conditions and examine the allowable shear values. Are there modifications to allowable values when the horizontal panel is applied to roofs? Consider the following two cases

1) The roof is typically broken up into sub-diaphragms. What is appropriate level of scrutiny that these sub-diaphragms should be subjected to? When can one say that the roof acts as one when do we have to start looking at them individually? Can someone describe the load path to me when the roof is broken up into regions or sub-diaphragms? Is it required to consider each plane as sub-diaphragm? If not, then up to what level may they be considered to act together?

2) On a different note, do we need to consider the degree that a horizontal diaphragm is rotated out of the horizontal plane? Where in the code can I find references to this?

Amir Zamanian

 

[111213]

amir,

start with a simple model, for example two rectangulars
braced by crossed tension diagonals.

elevate the middle-line so that there is an high slope roof and calculate the forces.

every force in the diagonals can converted in shear-forces.

calculate the displacements and decide if the stiffness is
big enoughto take the forces where do you want to have them.

 

[AmirZamanian]

111213:
Would you expand on your explanations?

 

[111213]

in which respect ???

 

[OldPaperMaker]

The APA has a booklet titled Diaphragms and Shearwalls Design/Construction Guide. It can be found On-Line at

http://www.apawood.org

I think that it is Form No. L350.
Example #12 of the booklet, "Design of a Subdiaphragm" shold answer some of your questions.