Simple truss 2

[dogarila]

This seems to be a fairly simple question but for some unknown reason no one is mentioning it either on the

http://www or

books on FEA and SW Simulation. Please take a look at the attached image and, please, let me know what do I have to do in order to analyze this truss with the restraints and load as indicated. All the applications or examples I found place the restraints and loads in the joints. What is supposed to be done when they are not located in the joints?

 

[MikeHalloran]

That's not a true truss. Truss elements are all columns, or tension rods.

On top, you've got a simply supported BEAM, supported by four column elements that are in turn supported by a BEAM that's continuous over two supports, with four concentrated loads at three points.

Assuming you have dimensions to locate the various points, the problem is soluble, but not a lot of fun.


Mike Halloran
Pembroke Pines, FL, USA

 

[dogarila]

Mike,
Ok, maybe my assembly it's not a truss, maybe it's just beams welded together. My question it's still the same. Asumming the supports and load location is known, what is the technique to define those positions in my simulation study? Do I have to break the bottom beam to insert joints at the supports? Do I have to break the top beam at the load location and create a joint? Are there other ways to do it?

 

[MikeHalloran]

A tool to analyze a truss will usually assume pin-jointed connections, that transmit loads but not moments.
I don't know if what you are using will make that assumption, or can be guided toward other sorts of connections.

I'm pretty sure that you could analyze the entire structure in the limited FEA package that comes with bare Solidworks, just by making it all one body, with no connections at all. ... i.e. subtracting volumes from a large rectangular solid, leaving you with beams and columns as appropriate. With a little extra work I think you can also model weld fillets that way. That way leaves you unable to model actual pinned joints, or shear joints, but for a fully welded structure it should get you close to representing reality.



Mike Halloran
Pembroke Pines, FL, USA

 

[dogarila]

Mike, I am using SolidWorks Premium which coes with static analysis of assemblies and multi-body parts. As I said, I found several tutorials on how to analyze this kind of structure. What I couldn't find and I am asking is how do I define the location of the restraints and loads that are not located in the joints.

 

[NickE]

you need to put features you can attach the loads and restraints to on your assembly. I normally use split lines.



Nick

 

[MikeHalloran]

Well, there's the answer to your actual question. Sorry to have confused the issue.


Mike Halloran
Pembroke Pines, FL, USA

 

[dogarila]

Thank you, Nick for your answer. I added split lines but they were not seen as joints so I couldn't use them to define restraints. I split the bottom beam and then I got the to extra joints at the support location and I could complete my analysis. I would prefer to use split lines tough because they are eaasier to add. Do you use them to create joints?

 

[NickE]

I dont use them as joints, what I do is use them on a face to create a region that is particularly restrained. and example is a spot weld, it would just be a circle on a surface to simulate the attachment of a spot weld...



Nick

 

[mmar2087]

Hi.
I guess your using the structural members with weldments.

When you do the 2d sketch, break the lines where supports and the force are positioned.
When you add structural members, they will be splitted according to your sketch.
In this way, simulation will add joints in these positions and then you can then put restraint and forces where you want them.

 

[dogarila]

Thank you guys for your answers. I gave you stars.

I was hoping that there was a more elegant way to tell the software where I want joints than actually model the joint and fool the software. One little problem I came across breaking a beam is that one side of the beam is too short and I get a warning message that the slenderness factor of that element is below 10. Is there a way to set this number?
Here's another question. I made reference points to apply my loads. For the force definition I pick a point, a plane, I select force normal to the plane and enter a value, lets say 100 lbs. So far no problem. If in the force definition I select 2 or more points (which the software allows) and enter a value of 100 lbs what is the meaning of it: 100 lbs on each point or 100 lbs spread across lets say 4 points, i. e. 25 lbs on each point? Simulation is not clear on that. In some cases it offers me the option to select total or per item but not in this case.

 

[mmar2087]

Hi.
As far as I know you can't set the slenderness factor to a value different from 10. This is a warning that you've reached the limit for beam theory and should consider other options.
Loads on beams are considered as "per item" so if you use two reference points and add 100 lbs this will actually be 2 x 100 lbs