Grasshopper

algorithmic modeling for Rhino

# Where does the horizontal force comes from

Hi,

I tried to make a truss in Karamba, but it gives me a horizontal force, while i have mad the supports as fixed supports. And the other question is am i doing it right with the truss?

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Hi,

I assume you mean the horizontal force as a reaction. Indeed, a fixed support (which you correctly created by restraining displacements in XYZ) doesn't allow any movement in any direction, so the reactions are vertical and horizontal. However as you can see in the image attach, rotation in your Y direction (that is, ortogonal to the truss) should be the one restrained.

Suppports.PNG

Hi Joseph,

I meant to make the supports Pinned. So the horizontal forces won't happend in the supports. I tried to make a Pinned support but it keeps giving me the horizontal force. I have changed the supports, but i dont reallt know if im doing it right.

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I think what you're looking for here is to make an isostatic structure. A way of making a beam (and a truss) isostatic is by creating a pinned support in one side and a roller in the other. By making this, you'll have no horizontal force at the roller, but you will have it at the pinned support. If you wouldn't, then the structure will be displaced.

Usually, in 2 dimensional structures, if you want to know if an articulated structure is isostatic (as opposed to hyperstatic, which is what you have right now) is to use the following formula:

b+c-2·n=0;

b being the number of bars, c the number of constraints you have and n the number of nodes. In your case: b=19, c=3 (displacements constrained in X, Z at your pinned support and only constrained in Z at your roller support) and n=11, so: 19+3-2·11=0.

I recommend you to download the app SW Truss, as it's very useful to check your results instantly.

Hi Joseph,

Thanks for your replies! I have it sorted out right now. That app is very usefull too to check if everything goes how it should be. Thanks a lot!

I'm glad you did, keep it up and good luck with that!

Hi Joseph,

I hope you can help me out here. I made a N - Truss and im trying to get supports on the top beams for the girders. But what support buttons do i need to check then. I know it cant be moved in the Z index but im not sure i did it right. Here is my file attached.

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Hi Giorgio,

I'm not quite sure I understand exactly what you want to do. Do you mean you want the truss to be hanging from the upper points?

Hi Joseph,

What i want to Try to make is that the truss is supported on the upper points by girders, like its a truss in a big hall of Steel. So the trusses are connected between the upper points. That will stop the truss to move in the z index.

Yours sincerly,
Giorgio

I think you're trying to do something like this:

Am I right? Like a spatial truss.

In that case, I think you can't do it if you divide both the top and the bottom chord at the same time, as you do here:

Perhaps you can try to divide the 2 of them independently and then use the points in the top chord as supports.

Hope it helps!

Yes, that is exactly what i mean. I have divided my points so the top points are selected and can be used as supports. But my question is to get the supports locked in the z-index so its supported like on the picture. I will add my file to it also. Now it shows on the screen purple numbers. I want to have the supports so the truss wont tilt to the Z index. I have a picture attached of what i mean. Thanks for so far!

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If you want no deformation along the Z-axis, just activate "Tz" on your Support condition:

I placed the Model View panel next to it, so it can be seen that at almost full deformation it shows no displacement along the Z-axis.

Hope it helps!