Shear Distribution

[jung8938]

I was hoping to get some advice on correct way to find shear distribution of timber walls along with steel brace frames and finding equivalent size of brace thickness.

Given the base shear, I assumed shear distribution from flexible diaphram and found equivalent thickness for brace frames by setting deflection of timber walls due to bending and shear equal to the deflection of 2D model steel brace (inverted chevron) frames. Then I went back to use the "thickness" to correct the shear distribution and so on..

Is this correct approach? Thank you for any advice in advance.

 

[csd72]

Your working late!

Are you talking about portal frames and shear walls in the same line or at different lines? Because for a flexible diaphragm the relative stiffness doesnt really come into it if they are separate points of support.

 

[jung8938]

I've been wondering about this all day...
Anyway, there are shear walls (timber) in one line that takes about 30% of shear and brace frame that takes about 30% in different line and another frame that takes about same in another line. (from flexible diaphram using tributary area)

To clarify, my procedures are as follow;
1. find distribution from flexible diaphram analysis using tributary area. Apply that shear to 2D model on one frame
2. find deflection and set it to theoretical wall deflection with assumed E,G with given geometry.
3. find thickness. use a software to find center of rigidity with shear walls including imaginary ones that are equivalent to brace frames with thickness obtained above, and update the shear distribution.
4. continue until desired degree of convergence is obtained...

sorry for long post and thanks again for any advice in advance..

 

[Lion06]

If you have a flexible diaphragm then you needn't worry about the center of rigidity (as csd notes above). The "thickness" or the stiffness of the shearwalls will not change the distribution of lateral forces for a flexible diaphragm.

 

[asixth]

jung8938,

I think you are confusing the shear distribution between 'flexible' and 'rigid' diaphrams.

The first statement of your second post is correct, the distribution of shear for 'flexible' diaphrams is based on tributary area.

The procedure provided in the second statement of your second post would be the procedure for analyzing a 'rigid' diaphram.

The distibution of shear to lateral elements for a flexible diaphram is based on the tributary area of the supporting element. This will give you a 'centre of rigidity' at the centre of the diaphragm.

 

[jung8938]

Thank you for the responses. I am trying to analyze both cases, and take the worse case scenario for the design. As I have mentioned above, I found out about the shear distribution using flexible diaphram by finding tributary areas.
Now I am trying on rigid diaphram to see how much they differ.

Thank you.

 

[Lion06]

You will likely have some frames/shearwalls that are controlled by a flexible diaphragm design and some controlled by a rigid diaphragm design.
Be sure to properly model your frame/shearwall stiffnesses so as to capture the torsional apect of your rigid diaphragm analysis.