EFFECTS OF FB ELEMENT AND FBPH ELEMENT

04-Unexpected behaviour/errors
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goksoy.cem
Posts: 4
Joined: 15 Dec 2020, 09:27

EFFECTS OF FB ELEMENT AND FBPH ELEMENT

Post by goksoy.cem »

Hello;

I have 2 models and only differeence between them is element class of columns. One of has force based element class columns and other one has force based plastc hinge elemetn class columns. However the force based model has about 0,85sec period and the other one has about 0,60sec period. Why the results are different like this? What can be reason of changing periods due to element classes?

Kind regards
huffte
Posts: 904
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: EFFECTS OF FB ELEMENT AND FBPH ELEMENT

Post by huffte »

Hi goksoy.cem. Your question intrigued me, so I created a simple model consisting of 2 cantilevers with identical lumped mass at the top. The only difference between the two cantilevers in the model is the element type - one uses infrmFB and the other uses infrmFBPH. I compute 6 modes from eigenvalue analysis with the following results. Modes 1, 3, 1nd 5 are for the first cantilever. Modes 2, 4, and 6 are for the second cantilever. The results for the two cantilevers, while not identical, are essentially equal. With the large difference you report, it seems that there may be other differences in the two models besides the element type. Maybe a detailed second look would be in order to see if this really is a problem. Best of luck.

M O D A L P E R I O D S A N D F R E Q U E N C I E S
Mode Period Frequency Angular Frequency
(sec) (Hertz) (rad/sec)
1 5.42102055 0.18446711 1.15904104
2 5.41761210 0.18458317 1.15977024
3 1.50281921 0.66541604 4.18093226
4 1.50261705 0.66550556 4.18149476
5 0.05170902 19.33898678 121.51043761
6 0.05170902 19.33898678 121.51043761
Tim Huff
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