Modal analysis for Pole structure supported by preloaded cables

Suby83

Hi all,
I would like to perform a modal analysis for a simple pole supported by preloaded cables.
For the cable behavior, a possible solution is to consider the CGAP elements. However, I couldn't consider this option for the linear modal analysis due to the non-linearity of the CGAP.
To better explain the test case I have attached a simple scheme of the problem.
Is there any solution to solve this problem?
Thanks in advance
Regards

 

Adriano A. Koga

CGAP could be used in linear analyis with no problem. The only aspect you should notice is that under linear, CGAP will act as a simple spring with same behavior under tension/compression.

 

In your case, you would need:

subcase 1: apply the preload force to the cables

subcase 2: modal analysis using STATSUB(PRELOAD) to take into account the change in stiffness coming from subcase 1

Suby83

Hi,
thanks for your kindly suggestion.
I have already tried to perform a preload modal analysis but I have noticed the following points of attention:

• the preload that simulates the contribution of the cable is always active: In the reality, if we have a flexural mode (for example the first mode) the cable with the traction effect is active while the cable with the compression is not active for the own mechanical behavior of the cable. Could this affect the shape modes and the related frequencies?
• the structure is symmetric and the balance of the force components gives a pure compression as highlighted in the attached picture.

For this reasons I thought that the solution wouldn't allow to right represent the reality.
What to you thinks about these considerations?
Could I test an alternative solution to solve the problem?
Thanks in advance