Column unbraced length
Column unbraced length
(OP)
I am analyzing an existing warehouse with columns that are 30' high to the roof. Problem is the columns are made up of 3 different sections. The first 10' of the columns are W8, the second 10' are HSS 8x8 and the last 10' are W8 again. What would be the un-braced length for each 10' section if the only lateral supported is at the roof.






RE: Column unbraced length
I didn't think architects designed warehouses.
I guess in a way you are looking at a step-column.
RE: Column unbraced length
I believe in trying the simplest thing first. Would the column satisfy your design requirements if it were only a W8x section? If not as TJ suggest it's a stepped column of some sort. I looked at the "Guide to Stability Design Criteria for Metal Structures" but the references there where appropriate to reducing columns steps, not smaller-stronger-smaller. There might be something out there on non-prismatic shapes to help you find a direction.
regards,
Michel
RE: Column unbraced length
RE: Column unbraced length
I'm attaching a paper on finite difference of non-prismatic columns to give an idea, but this case is simpler.
RE: Column unbraced length
I'd second WillsV's recommendation too.
RE: Column unbraced length
RE: Column unbraced length
What WillisV is saying would be appropriate as well. You can check the connection for whatever second order forces from the analysis to make sure they are sufficient as well.
RE: Column unbraced length
RE: Column unbraced length
RE: Column unbraced length
RE: Column unbraced length
Though I'd have to say that it is probably easier to set up, as WillisV suggests, a computer model and solve it using hte direct analsyis method.
RE: Column unbraced length
Regarding the direct analysis method, can you analyse it in RAM Elements?
RE: Column unbraced length
RE: Column unbraced length
I model the column as a hinge roller , roller in the gravity direction (to use K=1 in Euler equation).
I add a load on the top of the column and I run the bucking analysis
I get the Euler bucking load
From the Euler equation I get the RIGHT Inertia of the non-prismatic column
From then I can use the monograph or what ever method to get the K-factor