30 m high cantilever billboard column in low seismic zone

[nivoo_boss]

Hey everyone!

I have a chance to quote for a design of a 30 m high steel billboard column. It's located in Denmark, and the reference PGA in this particular area is agR=0,1 m/s². The design wouldn't be nothing too complex if it wasn't for the seismic part, which I've never done before. That's why I'm not sure I should quote for this thing.

I'm looking for advice. In reality, how much does this PGA affect this tall cantilever? Are there some simple methods to analyze this - perhaps even some that may be hand calculated? On top of the issue that I haven't done seismic design before, my current license for SCIA Engineer doesn't have seismic design.

 

[bugbus]

This is almost a textbook example. You have a structure with a single dominant mode of vibration (cantilever with concentrated mass at its end). It is going to be quite flexible and so will have a long-ish period of vibration. So, its response acceleration will probably be small. Given that it’s also in Denmark, I think the overall earthquake effect will be very, very, very small (particularly compared to wind effects).

But obviously you’ll need to crunch the numbers to satisfy yourself of that.

 

[phamENG]

That's why I'm not sure I should quote for this thing.

There should be no question here. You've never done it. You don't know how to do it. You should not offer to do it.

These sorts of signs have some very unique failure modes that are not obvious to someone who isn't familiar with them. Details that seem to help actually shorten the life span and can cause catastrophic failure. I would recommend not offering a proposal for this job.