Fundamental natural Frequency; Sign Poles

[signeng]

How do you calculate the fundamental natural frequency and damping ratio for a sign structure?

 

[Rich2001]

This site (Florida DOT) has a list of downloadable programs (mathcad sheets, etc) for the design of many highway structures.

http://www11.myflorida.com/structures/proglib.htm

If you don't have mathcad you might be able to load these in MathCad Explorer, downloadable from the

http://www.mathsoft.com

The natural frequency is a function of the mass of the sign and structure, the Young's Modulus and Moment of Interia.

 

[ishvaaag]

The fundamental frequency of an structural assembly properly modeled should be ascertainable from 3D programs with dynamics capability. Maybe even modest cost RISA 3D can do it even with hinge inserts. Respect damping ratio, Chopra gives
Under 0.5 Fy stress...
0.02 to 0.03 for nude steel welded structures
0.05 to 0.07 for nude steel bolted structures
Just prior to yiel Under 0.5 Fy stress...
0.05 to 0.07 for nude steel welded structures
0.10 to 0.15 for nude steel bolted structures
It is simpler to design in accord to a code, that in Spain exist, albeit it won't be suited for some high seismic places.
Respect attached weights (panels) the model should be as complete as to not need further separate (and worse) account.
Also is of relevance how account is made of Vortex Shedding, and of local over-pressures. Basically, either you design by a code, or you descend to the "truth" in the science of construction, what no doubt for cases will discover weaknesses of the approved codes for a thing like the one you attempt detailed analysis of.

 

[abhio]

Actually a sign would be pretty basic: it's just a cantilever (correct me if I'm wrong, and your sign is very complex). So the stiffness would be 3EI/L, and the cyclical frequency omega would be = sqrt(k/m).

 

[UcfSE]

I agree with abhio. Programs may be required for complex calculations, but for a sign, its just a cantilever. Make sure you're looking at the correct natural frequency. Omega_n is the angular natural frequency (rad/s) and the natural frequency f_n would be [Omega_n/(2pi)] (Hz).