huangyhg

handrail base plate
question for ya!
i'm trying to figure out if the baseplate i have for a handrail i'm designing will be sufficient. for some reason my units aren't calculating right. i'm using 1.5" steel tubing at a height of 48". i've calculated my moment at the center of the rectangular base plate to be 21 kip-in. if i want to use a base plate with the dimensions 2.5" wide by 4" long and an anchor bolt on either side of the handrail post, how do i make sure this thing isn't going to fail? i know it is based on a shape factor (s=bd^2/6) but for some reason my units aren't coming out correctly. thanks for the help!

i would think that if this is a handrail that needs to follow osha and ibc, the moment would be 0.2 kips times the height of 48" equaling 9.6 inch-kips.
assuming the vertical load is negligile, the anchor bolt tension times the moment arm to the centroid of compression under the base plate would need to equal the externally applied moment. the thickness of the base plate would need to be sized to resist the bending caused by the compression under the plate or the tension from the anchor bolt.
incidently, s=bd^2/6 is the section modulus and not the shape factor.
make sure that you clearly understand the theory before trying to solve this problem.
i'm following osha but using a factored live load (2.17 * .2 kips) * 48" = 21 kip-in.
i mistakenly typed shape factor instead of section modulus. it has been a long monday.
so, i have my moment arm to the centroid of compression as (2.5"/2 = 1.25"). where do i go from there?
first, check that the pipe wall itself is adequate for the load. then check the weld connecting the pipe to the base plate. you should be able to check the base plate itself using a method similar to that in aisc-asd for column base plates- essentially, assume that the plate is going to hinge near or at the pipe wall, and check moments about that point. there's probably not a fixed procedure for doing this, so results could vary.
consider also if your installation requires all of that load to be supported by a single post- quite often, the assembly will be adequate to distribute load around some.
your shape factor for a rectangular section is 1.5 (zx/sx) and the plastic section that you can use for the base plate analysis is b*d^2/4.
the force (lbs) in your anchor will be approximately m (in-lbs) / (0.9* 1.25") to approximate the depth of the compression block in the concrete base.
why are you using a load factor of 2.17? i would think 1.6 might be more appropriate.
daveatkins

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