Wood Shear Wall and Floor Diaphragm Design

[lagarza2]

As much as I can tell, I can follow most the recommendations for the design of wood diaphragms specified by the ANSI/AF&PA NDS-2005. Yet there are still gray areas which I hope someone can clarify. In the attached file you will find a typical example of what I run into. The attached file shows the first floor of a town home with the large arrow denoting the direction of the floor truss layout and shear walls denoted as hatched walls. In the design of shear walls when the wind is acting in the West-East direction, I am having questions on the load transfer from one side of the structure to the opposite side of the structure to engage the shear wall on the East side located in the living room. Also the NDS gives the allowable shear capacity of roof/floor panels, but the largest panel thickness supplied is 19/32” which is smaller than what is typically used in this area (1 1/8” normally used).

1) Is a drag strut to be designed to transfer the load to that location or can the floor be taken as rigid and assumed that that it can transfer the load to that shear wall location?

2) If I wanted to check the connection between the top of the shear wall and floor panels what design value would I use if the typical panel used in this areas is thicker than values provided by the NDS-2005?

3) Also does any have any comments on load transfer around openings in floor diaphragms such as the case in this particular scenario?

 

[msquared48]

With regard to drag struts (1), if you have interior shear walls, use them, rigid or flexible diaphragm.

Regarding (2), I'm not sure what your question is...

With regard to the sketch (3), you have to create sub-diaphragms and use additional drag struts as required to get the diaphragm to work.

Mike McCann
MMC Engineering

 

[KBVT]

You do not benefit from using a thicker sheathing panel if you are still using the same size nails as indicated in the NDS/IBC tables. You are probaly specifying 10d sheathing nails, which would limit you to the values 19/32" sheathing / 10d nail diaphragm capacity values.

 

[honat]

1)Use blocking to achive this horizontal shear transfer. You will need it anyway due to your different floor joist orienations

2)For your diaphragm chord force transfer to the vertical brace (shear walls) you could simply use skip struts between joist say every 3rd to 5th spacing depending on your chord forces(pound/linear foot)to fill the space between a regular deck 19/32" and top of wall. Once this scheme is well secured to the top of wall by the necessary nailing or screws. You can go back to NDS-2000 recommandation for 19/32" sheating shear nailing.

3) provide necessary deck with blocking around the opening to achieve a diaphragm beam.