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jjohnson
Posts: 21
Registered: ‎07-10-2008
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Beam Element to Truss Element connection

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11-27-2012 11:48 AM

Could you pleasse help me

 

I have a work platform with beam elements.  there are 2 metal chain to support oscillating floor frame.

 

What is the better option for simulate the chain? Beam or truss elements?

is possible to used Combined Beam and Truss Element Analysis in this case?

 

add pictures

 

Thank you

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AstroJohnPE
Posts: 570
Registered: ‎08-30-2012

Re: Beam Element to Truss Element connection

11-27-2012 12:31 PM in reply to: jjohnson

Hi JJ,

 

You can combine truss and beam elements in the same model.

 

There are a lot of options depending on what aspect of the chain you are trying to simulate:

  1.  If you know the chains will be in tension and are using truss elements to transfer axial loads only (beam elements would transfer axial and moment loads), then you must use one element for each section. Four truss elements total based on your images.
  2. If you do not know that the chains will be in tension but everything else mentioned above is true, then use gap elements instead of truss elements. Four gap elements total based on your images.
  3. If you want to see how the chains hang; that is, the catenary in the chains, then you need to divide the truss elements into numerous segments AND use MES to solve the simulation. Otherwise, the mutliple truss segments would result in a statically unstable model if you were running linear static stress.

Any one think of some other options?

 

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

Simulation Mechanical user since Dec 1997
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jjohnson
Posts: 21
Registered: ‎07-10-2008

Re: Beam Element to Truss Element connection

11-27-2012 01:21 PM in reply to: jjohnson

Thank you John

 

I am going to use this option:

 

chains will be in tension and are using truss elements to transfer axial loads only

 

I think using  end release en this 4 joint  (add picture).  What do you  think about them?

 

Thanks

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AstroJohnPE
Posts: 570
Registered: ‎08-30-2012

Re: Beam Element to Truss Element connection

11-27-2012 01:30 PM in reply to: jjohnson

I agree that you should use end releases on the four beams to simulate the hinge connection.

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

Simulation Mechanical user since Dec 1997
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Contributor
jjohnson
Posts: 21
Registered: ‎07-10-2008

Re: Beam Element to Truss Element connection

11-28-2012 10:10 AM in reply to: jjohnson

hello John

 

I have a final question

 

In a beam element How can I to represent a roller support.  Is it possible leaving free the X axis for the node or there  are another form?  add pictures respect roller support

 

Thanks

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AstroJohnPE
Posts: 570
Registered: ‎08-30-2012

Re: Beam Element to Truss Element connection

11-28-2012 12:47 PM in reply to: jjohnson

Hi,

 

You are correct again! Just leave the appropriate constraint directions unchecked so that the node can mode in that direction.

 

But based on your image, I think you want Tx to be fixed (checked) and leave Tz and/or Ty free to move. (I can't tell exactly how the roller is oriented, so you need to work on figuring that out.) If Tx is free, you are saying the node can move away from the wall but also THROUGH the wall. If it is safe to assume that the roller will stay in contact with the wall, then you need to fix Tx to get the support reaction. (If you know it does not remain in contact, then you would not put any constraint.)

 

You should also think about which rotations (Rx, Ry, and Rz) to fix, if any. The details of the design will dictate whether the wheel/roller prohibits the node from rotating about each of the 3 directions. Obviously, the node can rotate about one axis; otherwise, it is not a very good wheel!

 

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

Simulation Mechanical user since Dec 1997
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