Seismic load in Cosmos

Discussion created by sagar bafana on Oct 15, 2008
Latest reply on Feb 4, 2009 by sandeep pawar

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Hey everyone,

I have made a supporting strucutre which comprises of different I-beams in SolidWorks. I am wondering how can I apply seismic load to that structure.

Thanks for help

Sagar

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sandeep pawar Oct 15, 2008 5:05 PM
If you know how many 'g's the loads are going to be, both in vertical and horizontal direction, just goto Loads > Gravity and select the faces.

If you have 3g, just add gravity 3 times

Please correct me someone if I am wrong
- Sandeep
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Nur Kholish Majid Jan 9, 2009 12:49 AM
Hello All....

Any body can clarify on how to apply seismic load in simulation ?

@sandeep,

g=gravity ???
would you like to provice us some images ?

Thanks
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- Ameer Chilakala @ Nur Kholish Majid on Jan 12, 2009 10:23 AM
  Hi,
  
  For doing the sesimic analysis in cosmos, as per my knowledge we need to do in Simualtion premium product i.e. mostly customer will give you g verses frequency curve, this input we need to apply in random vibartions.
  
  Mr. sandeep mentioned we need to give as a 3g, it means it will apply 3*9.81 m/sec2 load in static analysis, if the customer mentioning the loading is interms of g means this procedure may be right.
  
  if customer is giving g verses frequency curve means, as per my knowledge we need to do a random vibration.
  
  But in Simultion Premium 2009 while doing the random vibation it will not support the beam mesh. so may be we need to apply the 2g or 3g gravity load in static analysis.
  
  kindly let me know if i mentioned anything wrongly
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Arun Prasad Jan 22, 2009 3:49 AM
Yes. I do a lot of seismic analysis for control valves. The values of `g` are generally specified by the customer as in OBE or SSE condition. We must know the values of g for horizontal and vertical directions.

Let us assume, its 2g in horizontal and 3g in vertical direction.

ie, 2*9.81=19.62 m/s^2 (horizontal) and

3*9.81=29.43 m/s^2 (vertical).

In Solidworks Simulation, start a static study-> go to External Loads -> Gravity.

Here, selected reference plane must be Front or Right Plane. Apply the vertical gravity force(29.43 m/s^2) in the Earth`s gravity tab(Apple Icon) and then reverse direction. This completely defines vertical gravity.

Similarly, Click advanced Tab, Apply horizontal force as in the desired direction(19.62 m/s^2).

Actually, there is confusion with respect to the third direction. As safety is a prime concern in our industry, we apply
horizontal force(19.62 m/s^2) again on the third direction. This may not be required. But, we apply the third direction force so as to protect the valve against possible failure. I mean, naturally, the FoS is increased.

Why don't we theoretically verify this seismic load condition by solving some problem manually. Any Suggestion??
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- sandeep pawar @ Arun Prasad on Feb 3, 2009 8:53 PM
  Arun,
  
  Can you elaborate upon the face selection. How do you select the face. Since teh entire valve structure is going to under seismic load, what face do you select for loading?
  Please upload a picture, if possible.
  
  Thanks,
  Sandeep
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David Anderson Feb 3, 2009 9:52 PM
Hi,

If you are performing a seismic analysis on a structure, then there is a bit more to it than applying a static load.

I am delving in to seismic analysis' (using ANSYS) and ccording the the ASCE 07 handbook, seismic loads are given as g's vs t and are location dependant. because the g loads vary wrt to time you must perform a time history analysis to see how the structure responds to the inputs. this will require a nonlinear, rather than a linear solver.

a simple static load will tell you displacement and stress, but does not give response of the structure to a load that varies with time.

the base motion profile is dependent on location and looks something like the image attached for area code 90210.

check out

http://earthquake.usgs.gov/res.../design/#install_java

they have a neat little tool you can use to generate the seismic profile.
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- designspectrum.JPG57.9 KB
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Arun Prasad Feb 4, 2009 7:29 AM
Hi Sandeep,

See, I never told abt Face Selection. Its only Plane Selection.(Right/Front). See, when we stand on earth, there is gravity force that is pulling us downwards. Its not that gravity force is acting on our foot. Suppose we have a Solidworks Model of human body. If we restraint the base of the foot, how would you apply gravity? Which Face? or Which Part?

The gravity is acting on the body at CG(Center of Gravity) or Center of mass. So, we need to select the respective planes for horizontal or vertical gravity.

as an example, take the case of a pyramid with base fixed. Check the direction of plane on the screen shot
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- Arun Prasad @ Arun Prasad on Feb 4, 2009 7:31 AM
  
  Arun Prasad wrote:
  
  Hi Sandeep,
  
  See, I never told abt Face Selection. Its only Plane Selection.(Right/Front). See, when we stand on earth, there is gravity force that is pulling us downwards. Its not that gravity force is acting on our foot. Suppose we have a Solidworks Model of human body. If we restraint the base of the foot, how would you apply gravity? Which Face? or Which Part?
  
  The gravity is acting on the body at CG(Center of Gravity) or Center of mass. So, we need to select the respective planes for horizontal or vertical gravity.
  
  as an example, take the case of a pyramid with base fixed. Check the direction of plane on the screen shot
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  - 090204-145422-1680x1050-F.jpg488.4 KB
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  - sandeep pawar @ Arun Prasad on Feb 4, 2009 12:24 PM
    Thanks Arun. If you have any case study please let me know. Thanks.
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Seismic load in Cosmos

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