Casey
Well-known member
When calculating the wall weights to be used in for the seismic weight I see two approaches when dealing with the ground floor (or a single story building)
The first one is that the entire height of the wall is considered as part of the seismic weight. Williams likes to do this in his examples.
The second one is that only the upper half of the wall is considered as part of the seismic weight. Ref SEOC Seismic Design Manual Vol III Ex 1A page 11. The author applies the upper half of the ground floor wall to the second floor. Similarly for Ex 3 pg 127
Is using the entire wall just a conservative approach? Or is there a decent justification out there?
I personally agree with the second approach as I visualise the weight from the lower half of the wall being distributed to the foundation and not the SLRS. Can anyone show me why this approach is not appropriate?
As for parapets, I notice there is two trains of thought on how they along with the wall below the roof should be distributed to the roof diaphragm. One approach is a straight forward tributary calculation with exactly half the wall between the roof and floor below going to the roof diaphragm (the upper half obviously) plus the full height of the parapet. (SEAOC Seismic Design Manual Vol I pg 165-166 does this)
The other method ratios the total height with parapet over the height of the level below (basically treats as a simple beam with an overhang) [sEAOC Seismic Vol II Ex 5 pg 260]
Again, other than one method being slightly more conservative than the other I don't see a huge difference. Can this one be chalked down to design preference/laziness? Or is there a particular reason why I should follow one approach over the other?
Any input would be great.
Thanks
Casey
The first one is that the entire height of the wall is considered as part of the seismic weight. Williams likes to do this in his examples.
The second one is that only the upper half of the wall is considered as part of the seismic weight. Ref SEOC Seismic Design Manual Vol III Ex 1A page 11. The author applies the upper half of the ground floor wall to the second floor. Similarly for Ex 3 pg 127
Is using the entire wall just a conservative approach? Or is there a decent justification out there?
I personally agree with the second approach as I visualise the weight from the lower half of the wall being distributed to the foundation and not the SLRS. Can anyone show me why this approach is not appropriate?
As for parapets, I notice there is two trains of thought on how they along with the wall below the roof should be distributed to the roof diaphragm. One approach is a straight forward tributary calculation with exactly half the wall between the roof and floor below going to the roof diaphragm (the upper half obviously) plus the full height of the parapet. (SEAOC Seismic Design Manual Vol I pg 165-166 does this)
The other method ratios the total height with parapet over the height of the level below (basically treats as a simple beam with an overhang) [sEAOC Seismic Vol II Ex 5 pg 260]
Again, other than one method being slightly more conservative than the other I don't see a huge difference. Can this one be chalked down to design preference/laziness? Or is there a particular reason why I should follow one approach over the other?
Any input would be great.
Thanks
Casey