Averaging point load on API tank roofs?

[alan54]

Does anyone have any rules of thumb for how much area you can spread a point load over for an API-650 self-supported conical roof? For instance, Brownell & Young show the derivation of design equations for a 25 PSF live load on a 3/16" thick roof. A 200 LB man standing with his feet side and side is a 200 PSF load but the roof holds him, so ovviously the design rules allow for the load to be out to some degree.

The was a related '07 thread 809-174969 where responders said to design platform so all support legs are on the shell; this is good advice for a new tank, but in this case it is an existing tank and all support legs on the platform are already on roof, and we need to add some load to the platform. That thread mentioned WRC-107 but the D/t is way beyond the limits for WRC-107.

Thanks!

 

[JStephen]

One of the building codes specifies an area (seems like 30"x30") for a man-type concentrated load, but this relates to loading, not to the structure, and would not be applicable where you had supports landing on a roof.