shearwall heigh

huangyhg

shearwall height
this is a pretty basic question about shearwall height. let's say i have a 1-story house with 8' stud walls. the framed wall rests on the floor system, which consists of 2x12 joists (see attached .jpg file for a cross section).
for the shearwall height, do i use 8' or  8'+ depth of the floor?
quote:
for the shearwall height, do i use 8' or  8'+ depth of the floor?
in what context?  what are you attempting to do?  depending on what you are doing, it could be either.
ba
hi ba,
for example:
1) checking the maximum height to width ratio for shearwalls (ibc table 2305.3.4)
2) calculating the load/ft to the roof diaphram (do i use 8'/2*wind pressure, or 9'/2*wind pressure).
3) calculating the holddown loads: (unit shear) x (wall height)
thanks for your help.
it's to the top of the foundation, 8' + floor, section 2305.3.5.  why is the wall resting on the 2x12?  seems to me to be a waste.
hi sandman,
i found the section in the ibc that you referred to - the shear wall height is defined as:
1. the maximum clear height from the top of the foundation to the bottom of the diaphragm framing above.  
for reference, i've attached the figure from the ibc.
maybe i'm mistaken, but "clear" height would seem to mean from the top of the floor sheathing to the bottom of the diaphragm framing above.  if you look at the 2nd story in the figure, the clear height goes from the floor diaphragm below to the bottom of the framing above.  i guess my confusion is this:
for the shearwall height of the 1st story - do you measure the height from the mudsill that rests on the foundation, or from the 2x plate that the wall studs rest on?
also, i don't understand your comment about the wall resting on the 2x12 being a waste.
1:  per the diagram to the underside of the floor/roof diaphragm framing... i.e., to the top of the associated double wall plate.
2.  9'/2, but this would be for a single story structure.  for a multi-story structure, it is the distance between the floor/roof diaphragm plywood above and the floor diaphragm plywood below divided by 2.
3.  diaphragm plywood to top of concrete foundation wall or footing.
  
mike mccann
mmc engineering
hi mike,
thanks for your answer... i'm not quite clear on number 1: for checking the maximum height to width ratio, would i use 9' as well? [9'=from the top of the stem wall to the top double plate, or 8'=from the top of the floor joists (diaphragm) to the top double plate].  please see the picture i attached in my first post - do i measure the height for the ratio from the top of the foundation stem wall, or from the top side of the joists (where the wall studs rest)?
thanks for your help.
the code seems to be addressing how the sheathing will react to lateral loads.  it requires that your shearwall segments act like deep beams with, what i would think, is a very stiff wall section.  this exercise is intended for determining the maximum lateral shear your wall will take.  this section should not be used for addressing how your loads (wind and seismic) are distributed to the diaphragms or how you will need to anchor your shear wall.
ex. using this calculation i can determine that wall a can resist ## kips of lateral shear.  i only need it to resist # kips.  ok, i do not need another shear wall in this direction, now i will design the connections.

i have a wall that has a lot of windows in it.  i'd like to use as many of the full height wall segments as possible for shear walls, but i need to check that they meet the height to width requirement.  so my question is: when checking this ratio, do i use 9' (from the top of the stem wall to the top double plate), or 8' (from the top of the floor joists and sheathing where the the studs rest, to the top double plate).
my thought is that the latter height (8') is actually the "clear height."
short answer - 8'
for all intents and purposes, the top of the floor acts as a fixed base and the bottom of the next floor's joists act as a fixed top.  the shearwall is then checked for empirical stiffness.
quote:
1) checking the maximum height to width ratio for shearwalls (ibc table 2305.3.4)
2) calculating the load/ft to the roof diaphram (do i use 8'/2*wind pressure, or 9'/2*wind pressure).
3) calculating the holddown loads: (unit shear) x (wall height)
i am not familiar with the named code, but i believe:
1)  use clear height for h/w ratio.
2)  use clear height/2 plus roof thickness plus parapert height.
3)  use total height above concrete foundation for holddown loads.
at least, that is the way which makes sense to me.
ba