huangyhg

beam supporting masonry
curious what others are using as an allowable deflection for beams or slabs supporting masonry. i know aci530 states span/600 but not more than 0.3 inches for unreinforced but i've been seeing it a lot on thin pt flat slabs and cantilevers that certainly don't meet this criteria. i realize that it's often concealed so some cracking is tolerable but how much deflection is too much?
check out our whitepaper library.
i follow aci 530. but if you can accurately predict when the masonry will be laid, some of the beam load can be omitted from the deflection calculation (e.g., if the roof or floor framing is installed prior to the masonry being built, the dead load deflection will already have taken place and need not be considered in the deflection check).
daveatkins
"the brick industry association" allows the span/600 or 0.3 inch (max) deflection under full load (probably where the aci requirement came from). i go with that. here is a link
if it's reinforced masonry, typically i use the span/600 and omit the 0.3-inch limit. for unreinforced i would use the same but include the 0.3-inch limit. that's used with the d+l combo.
the rupture stress of the masonry assembly and the use of the masonry assembly will have to be known to make any judgement on how much deflection is tolerable. can you live with a cmu wall completely cracked through the face shell? what if it is used to resist lateral loads?
don't forget, if it is a long span lintel, to have control joints at the lintel ends. the end rotation of the lintel can cause cracking of at the ends.

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]