huangyhg

wood king stud
i've got a 20'-0" high wall on a project that has an 8'-0" wide opening. based on 20 psf wind load the king studs would have a distributed load of 80 lb/ft and need to be (4) 2x8's. the contractors say this is excessive and it does seem to be, but i can't work the numbers out any other way. is there anything i'm missing,does the window frame itself transfer some of the load?
thanks,
how many other openings on the wall and what is the wall finish?
i have seen drywall cracking problems due to wind loads on tall walls where the strength was ok, but the deflection caused the cracking. extra openings caused points for the cracks to begin. especially important if you are situated where you can get wind gusts that can cause momentary deflections.
dick
is the contractor the engineer?
if the opening is 8' what is the spacing to the next vertical
they jamb would see half the window plus its own width plus half the distance to the next stud. i don't think you're all that unreasonable. it's a 20-foot span with a fairly wide opening. what you can do is go back to your calcs and sharpen your pencil and remove the simplifying conservative assumptions, such as uniform loading, and try to more accurately assess the loads. you'll have uniform load from the width made up of half the stud spacing plus jamb width. you'll have linearly varying loads and point loads from the window and header, and uniform loads for half the cripple stud spacing below the sill and above the header.
the problem is, you'll have to do that for every window instead of once for every 8-foot window. in the end, it is what it is.
are you able to refine the 20 psf wind load that you are using to something lower? what code are you using?
20 feet is a tall wall. a rule of thumb is to add a stud for each one that was cut out (a little conservative). for 8', that would roughly be 5, so add three to each side to make it even. that means 4 - 2x6 studs should work. if it doesn't, then 1-2x6 @ 16" doesn't work either. my gut feel is you need 2-2x6 studs @ 16" for that height wall. the required king stud width will probably be getting rediculous, so a steel tube or channel may be in order in place of some of that wood.
i agree with jike - double check the wind pressure. i don't know your location, building geometry, or anything else, but the component has a relatively large effective area and you may be able to get a smaller wind load.
thanks for all the responces. i was pretty confident my calcs were correct. i have in the past reduced wind load as much as i could and more accurately imposed the loads onto the studs but have always come up with large king studs on these two story walls. i just wanted some confirmation that i wasn't missing anything.
if im not mistaken, your king stud should see 8/12 x 20 psf (13.3 plf) span of wind along the whole stud, and a point load at the header location of (4'x height of wall above the header x 20psf). i am not sure how you got 80 plf.
the point load at the header/window sill end connections should also include the tributary wind load from the window itself.
oh yes whyun.. doh.. yeah, so the point load should be (4'x10'x20psf).

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