[SAC-HELP] Dynamic modelling

Belema Altraide Belema.Altraide at arup.com.au
Sun Sep 21 23:52:00 PDT 2008

To whom it may concern

I have modelled a jacket (file attached) and have performed a dynamic analysis on the structure (extract mode shapes). I have fixed the sturcture dynamically on four corners of the jacket and the topsides 222000. At the base of the structure, there is a central joint 2001 (at EL-180) that has spring values applied on them and these values are:
vertical: 7000MN/.
Lateral: 2500MN/m
Rotational: 8E6MN/radian
Torsional: 4E6MN/radian

I analysed the structure with these applied spring stiffeness values and the 4 joints 21,22,23,24 dynamically fixed in all directions (222222) and am getting a period of 44 sec with the structure rotating vigorously.

I need some help with the following:
1. I am unsure how to apply the spring values from joint 2001 to the four corner joint 21,22,23, 24. At the moment, I assume that I will need to rigid link joint 2001 to the four corner joints?
2. If 2 is correct, I am unsure how to rigidly link the joint 2001 with the spring stiffness values to the four corner joints 21, 22, 23 and 24.
3. I am unsure what fixities I need to apply to the four corner joints.

Your help to the above queries would be greatly appreciated. Please help me asap.


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