High Stiffness Elastic Elements

03-Analytical/modelling capabilities
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rashid
Posts: 26
Joined: 05 Apr 2014, 16:27
Location: Christchurch, New Zealand

High Stiffness Elastic Elements

Post by rashid » 04 Feb 2019, 03:41

Hi All,

I've modeled a lumped plasticity model of an RC frame. It is designed to capacity design principles and the joint flexibility can be ignored.
My objective is to get the floor acceleration response histories and not a detailed assessment of the structure itself.

Do you have any suggestions on how to model the beam-column joint region of RC frames in such cases? Traditionally, elastic members with very high flexural stiffness have been used to model the panel region. However, what constitutes very high flexural stiffness is undefined. I personally keep on increasing the flexural stiffness until the time period becomes insensitive to it (I have an estimate of the time period from other studies).

Based on my experience with different frames, such high stiffness leads to a very weird response of the elastic beam-column elements attached to these panels in pushover analysis (see link below). Also, I have got this concern that such high stiffness might lead to unreliable damping estimates, would it?

https://www.dropbox.com/s/9z4c9lhzzsv6k ... e.png?dl=0

Your help will be much appreciated.
Muhammad Rashid

huffte
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Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: High Stiffness Elastic Elements

Post by huffte » 04 Feb 2019, 15:06

Hi rashid. If joint flexibility can be completely ignored, I wonder if rigid offsets (defined in the element connectivity dialogues) at the member ends might suffice?
Tim Huff

rashid
Posts: 26
Joined: 05 Apr 2014, 16:27
Location: Christchurch, New Zealand

Re: High Stiffness Elastic Elements

Post by rashid » 05 Feb 2019, 11:04

Hi Tim,

Thanks for your suggestion. I'm wondering if a model with rigid offsets can be used with the lumped plasticity approach. A model with rigid offsets would include beams and columns with center-line dimensions and connected at one node at a joint. We can then account for the joint panel region by making a portion of the column and beam length rigid offset.
Since lumped plasticity (link element) would require the definition of an extra node at the end of the rigid offset (which is the face of the column in case of a beam), therefore I do not think so this approach can be used (as the element is continuous). Please correct me if I am wrong.

Best regards,
Rashid

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