building drift and diaphragm deflection limits
 

building drift and diaphragm deflection limits
where do i find some good information (with a picture preferably) on
1. building vllr drift limits
2. diaphragm deflection limits between the mfrs.
i have design guide 3, but that all seems greek. what do they mean drift perp to wall? which wall, the shearwall or the wall which is perp to this wall. i know you always hear h/400 for the vllr, but why. where is that written in stone, and why can a prefab building drift so much more.
thanks for any help.
depends on what you are designing for. there are seismic drift limits in the ibc code. design guide 3 is for serviceability and yes it is very hard to read. pre-engineered metal buildings are allowed a limit of l/120 regardless of cladding, which i think is a political thing...lobbyists and all for the metal building association. if you have masonry veneer, then you should use somewhere between l/600 and l/480. a masonry association recommends l/730, but that gets a little crazy. i would use design guide 3 except i would use the masonry veneer limit above. another thing you can consider is you wind speed. it is based on a 50yr occurrence. who cares if your brick cracks a little in 50 yrs. you can adjust your serviceability design wind speed by converting it to a 10 yr wind speed and reduce your wind speed by around 30%. the conversion chart is in the back of asce 7. makes a pretty big difference if you can't meet your serviceability drift limit. you still want to set your strength limit using the standard wind speed.