huangyhg

height to thickness ratio of a reinforced masonry wall
i am designing a cantileavered reinforced masonary wall. what is the maximum height to thickness ratio allowed by the code for this type of wall? where may i find a code reference to this issue?
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1997 ubc sec 2107.2.14.2 indicate h'/t = 30 as a dividing line between slender and non-slender wall. i am presuming your situation is an exterior masonry wall with a cantilevered parapet above the roof level.
i am not aware of an absolute maximum ratio but statically, you can't avoid having a very thin wall and make the wall work out as height increases.
out-of-plane slender wall design at strength level is in sec 2108.2.4.
whyun
thanks for the reply. i will give you a little more detail of the wall i am designing. the will is a free standing cantileavered firewall exposed to wind load only. in this case for the h/t value. would the "h" value have a multiplier of "2"?
if the wall is resisting wind load only, the h/t ratio is not an issue. the h/t ratio affects the allowable axial stress, fa, but not the capacity of the wall in bending.
i am in partial agreement with dave. h/t does affect the wall when subject to vertical loads and out-of-plane lateral loads. moment on the wall will have contribution from flexure, eccentricity of applied vertical load, bending due to maximum flexural displacement of the wall. high h/t will result in making the third term very large.
i agree with dave that h/t is not an issue with a freestanding wall. disgrgarding the h/t, design the wall first and see that h/t comes out to. regardless of the height, you would use a 6" wall at a minimum, probably a 8". in the end h/t wont look so bad.
i think you need to check: fa/fa+fb/fb < 1.00 (or 1.33 ? )where fa is axial compression due to dead load and fb is flexure compression due to wind.
i think code (asce 7-98) does not allow 30% stress increase in wind load combination i am not sure about aci-530. any comments ?
for a cantileavered wall effective height h'=2h
check the website for the national concrete masonry association (ncma). they have a series of tek notes that address all aspects of concrete masonry design and constrution. you can order their publications or if time is short, you can find a member firm near you and get copies. i found a ncma member firm that had a link to the tek notes.

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