huangyhg

building joint spacing
i have a two story school i am designing that is apperoximately 320'x100'. the structure is masonry loadbearing walls at the perimeter and along the interior corridor which runs down the middle of the building parallel with the 320' exterior walls. the second floor is metal joists with non-composite metal deck + concrete, and the roof structure consists of steel joists and metal deck. my question is if i need a building joint to break up the 320' length. the loadbearing masonry walls have control joints about 24' on centers and the cmu bond beams are continuous through the control joints at the roof and the 2nd floor.

others will have different opinions, but i would place an expansion joint at mid-length. and i would use control joints at 20' centres, with the bond beams discontinuous at the joints.
you are going to need a shear wall in the 100' direction. you're not going to get the deck to work at a 3:1 aspect ratio. that's a good place to locate your expansion joint.
frv,
i do have a few shear walls in the 100' direction.
i was thinking i would not need an expansion joint because i have cj's in the cmu. i know the cmu walls will still have alot of stiffness at approximetly 24' in length, but i was assuming this would still allow for some expansion and contraction of the 2nd floor and roof diaphrams. it can't be any more stiff than having a steel framed building 300' long with braced frames located at each end of the building.
how much trouble would it be to put a building joint near the middle of the 320' direction?
imho, at 320' you are right at the 'do it/don't do it' line. if it was reasonably easy to put the joint in, i would do it and sleep well at night.
if it will be difficult to get the joint in, with some proper detailing, you can make the 320' work.
without a joint, i would tend to break my bond beams every 2 or 3 joints to allow some shrinkage movement by the cmu walls at the bond beam elevations.
jmho.

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