huangyhg

work table leg design
hi,
i'm trying to design a work table for our shop using 4x4x1/2" and 5x5x3/8" hss members for legs. the legs are to be adjustable in height with the smaller hss "nesting" in the larger. the table height is to be adjusted using the nested hss and inserting a pin through the two members.
i think i have a handle on the shear stresses in the pins but when considering the compressive stress at the pin holes, would it be too conservative to assume the stress is concentrated over a area equal to the diameter of the hole times the material thickness? ie d x t ?
any suggestions on how to treat this ananlysis would be appreciated.
the compressive stress to which you refer is also known as bearing stress. the aisc code allows us to do just what you have said: compute the bearing area as diameter of pin or bolt times thickness of the material d*t. this area is called the "projected bearing area". this is then compared to the allowable bering stress, or maximum bearing reaction, based on the code equations.
if you are using the aisc manual, you will find this information in section j.7 of the 9th edition asd manual or in j8 or the 3rd edition lrfd manual. the aisc is a structural code used for buildings and some bridges. if you are under a different code, then of course you'll need to find the proper location and be sure to follow its requirements.
thanks. i'm using the handbook of steel construction (canadian institute of steel constrution).
keep in mind the building code is intended for joints bolted together, with the pieces clamped by the bolt, with a hole just slightly oversized, and even at that, allows for some yielding at the bolt. for a removable pin, you're liable to have more oversized hole, no clamping, repeated loading with pin in slightly different positions, etc., so you'd probably want some extra conservatism there if possible.
the formulas in can/csa-s16.1-m89 differentiate between bolted connections and machined or fitted parts with the latter formula being more conservative. you are also correct about the oversized hole, i planned on 1/16th of an inch diameter over the pin size.
i just finished the calculation and it leaves me with a s.f. of 5.02 based on the 5x5x3/8" hss.

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