New platform on circular metal chimney
New platform on circular metal chimney
(OP)
I am trying to expand an existing platform on a 14'-0" diameter metal chimney. Currently, the chimney has an octagonal platform which is support with knee braces. At the platform elevation the platform beams frame into a rolled C8x11.5 with the C8 flanges pointed outwards and at the chimney/knee brace interface (@ minus 4'-0" from Top of Steel) the double angle KB gusset plates frame into a rolled L4x4x0.25.
My question is how should I analyze the metal chimney for the local and global effects of the additional DL, LL, Wind Loads?
My question is how should I analyze the metal chimney for the local and global effects of the additional DL, LL, Wind Loads?






RE: New platform on circular metal chimney
It would really really help to have the original design calculations for the stack, or to be very familiar with the design of stacks in general. For example, does that rolled angle or rolled channel act as a stiffener for the top of the stack, or are they just there for the platform? Or does the whole platform framing act as a truss-type stiffener?
If it's a very tall stack, the additional vertical loads may be negligible compared to wind bending loads.
Note that Roark's Formulas for Stress and Strain has stress equations for circular rings with uniform radial loads, which may be helpful for some of that.
RE: New platform on circular metal chimney
For the global effects, I would first try to demonstrate the the incremental load effects were small enough to be ignored. Failing that, I'd fire up my calculator for a workout.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: New platform on circular metal chimney
Also, it would be expected that plate stresses at the top of the stack would be low, unlike at the bottom.