I am running a model currently and have found that my normal modes and pre stiffened modal analysis are very similar. I am wondering if there is a way of validating my results via a simpler model or hand calculation. I am using the sol103 with STATSUB method to analyse the pre-stiffened model.
Also does anyone know of any good sources on modal analysis specifically pre stiffened modal analysis.
Any help will be much apreciated!
Unless you have long flexible members under primarily normal load (tension / compression), you won't see a difference. For most normal structures you might notice a few percentage point difference, because most structures aren't like a guitar string (the classic example of preloaded vibration).
Just a side note, tensile load increases the local natural frequencies, while compression lowers them. Local bending loads have no effect on natural frequencies (theoretically, mathematically). Global bending loads, which express themselves as purely tension in one member, and compression in another, of course have an effect.
A screenshot would be great.