topic Pin jointed truss model in Robot Structural Analysis Forum

Pin jointed truss model

howard.irons — Sun, 02 Feb 2020 14:36:32 GMT

How should the attached pin jointed truss be modelled to ensure stability of the model?

The structure should be stable in practice but indicates instability in the model.

All members are modelled with pinned releases at each end to reproduce pin jointed truss conditions.

Thanks

Howard

Re: Pin jointed truss model

Rafacascudo — Sun, 02 Feb 2020 21:59:16 GMT

if is just a "perfect" truss model , use "truss 2d" structure type on Gemotry/Strucutre type . Connections will be automatically pinned . No need to use bar releases

Re: Pin jointed truss model (UNCLASSIFIED)

howard.irons — Sun, 02 Feb 2020 23:12:59 GMT

Classification:UNCLASSIFIED

Thanks Rafascudo, after I sent the post, I found that structure type and got the results I needed. Out of interest, do you know why the releases cause such a problem in the 3D structure type? This is a common instability problem I have encountered in Robot when I put releases into the model. Any tips on this would be appreciated.

Re: Pin jointed truss model (UNCLASSIFIED)

Rafacascudo — Mon, 03 Feb 2020 00:25:43 GMT

For a 2d truss on 3d enviroment you do not need torsion and out of plane moment releases(Rx,Rz).

Also ,on a node that has several bars converging , one of the bars has to be unreleased or an instability warning will show up. This happened on your model.

On a real world truss ,where chords are continuous ,you can use regular bars for the chords and truss bars(geometry/additional atributes/advanced bar properties) for diagonals , and forget about releases

Re: Pin jointed truss model (UNCLASSIFIED)

howard.irons — Mon, 03 Feb 2020 17:07:00 GMT

Classification:UNCLASSIFIED

Thankyou, I will note this for the future.