Spring and dashpot

02-Getting started with the modelling
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bassking
Posts: 8
Joined: 21 Feb 2012, 12:28

Spring and dashpot

Post by bassking » 15 May 2012, 17:39

Hello, i'm study the seismic behavoir of a bridge with particular attention to the soil structure interaction and i need to know how to model a spring and a dashpot who work in parallel. For the spring i use a zerolenght element, for the dashpot i use dashpt command, I'm i doing it right? Do the spring and dashpot work in parallel?

huffte
Posts: 838
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: Spring and dashpot

Post by huffte » 15 May 2012, 18:45

Bassking, I believe:

1. that as long as the dashpot node is defined to be the same as node 2 for the link and
2. node 1 for the link is fixed to the ground

You should get parallel behavior between the two elements.

At least this is my understanding. Best of luck bassking.
Tim Huff

antonioacorreia
Posts: 5
Joined: 02 Oct 2010, 12:42

Re: Spring and dashpot

Post by antonioacorreia » 20 May 2012, 05:38

Dear Bassking,

There are two options for modelling a parallel spring+dashpot:

1. The one provided by huffte in the previous reply:
- a common moving node for both the link and dashpot elements;
- a fixed node for the other extremity of the link (the dashpot element already assumes it is connected to the ground and uses the relative velocity to compute the damping force);

2. To simply use a link element with the appropriate stiffness and to define the corresponding damping directly at the link dialog box.

The latter one is probably the best choice, as pointed out in SeismoStruct's help system.

Best regards,
Antonio

Abu
Posts: 1
Joined: 12 Nov 2012, 01:31

Re: Spring and dashpot

Post by Abu » 12 Nov 2012, 07:25

Dear Bassking,

I am trying to model the SSI for a bridge pier using spring & dashpt element. I was wondering whether you were able to model that? If yes, would you please help me in this regard.

Thanks.

gkcve
Posts: 2
Joined: 17 Sep 2018, 23:40

Re: Spring and dashpot

Post by gkcve » 19 Oct 2018, 12:48

Hello Everyone.

I have a question regarding the natural period increase when accounting for Soil-Structure-Interaction (SSI).

I have modelled the soil with nonlinear springs by adapting the Ramberg-Osgood model to my G-γ-D curve. Previously, I used linear springs to simulate the soil. Now, I am trying to compare the differences between the two simulations and I have observed different increase of the fundamental period with SSI for the two models compared with the natural period in fixed base case.

Could you please tell me whether this is caused due to the fact that Seismostruct considers different initial stiffness for the linear and nonlinear springs e.g. for the nonlinear might take the secand instead of tangent.

Many thanks.

George

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seismosoft
Posts: 594
Joined: 06 Jul 2007, 04:55

Re: Spring and dashpot

Post by seismosoft » 25 Oct 2018, 11:56

In eigenvalue analysis the initial tangent stiffness of the section is considered. This stiffness can be reduced in the relevant settings are changed in the Program Settings>Cracked Stiffness module
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