Truss Bars and Deflection

[Anonymous]

Hi, I’m trying to convert some of my bar members to truss members, however I get instability errors (Type 1 in UZ direction) along two of the bars where there are isolated nodes when converted. These errors are not there when they're normal simply supported beams.

I need to keep those nodes there for reference, but they shouldn’t be causing any issues. Has anyone ever come across this.

[Rafacascudo]

These 2 nodes are on 2 truss bars. Why do you need them?

Deleting them makes the model run without instability warnings.

[Muhammed.OPERA]

Hi @Anonymous

I see you have made that members (Purlines) to be truss members, just undo that as they will have to carry the cover with loads and assign releases on the extreme points of it as in the pic. and everything will be alright.

[Anonymous]

I've applied planar loads to the cladding over a small area, I created nodes to select that area. Although I can delete them, I may need them just to check the coordinates at a later stage. How come they have an effect on the stability? 

Thanks 

[Anonymous]

Hi thanks for the reply, I intended to have those members as just a bracing system. You can see that they only carry axial loads as well, as i've distributed the cladding loads directly to the chords and columns. There will be additional purlins running the length of the building on top.  Similar to the image below but with purlins. 

[Muhammed.OPERA]

Hi @Anonymous

In that case keep it as it is and just delete the nodes (you can replace them by axes if you want for some purpose) and be sure that the load you applied (uniform planner load with contour) won't be changed.

[Anonymous]

Thanks Muhammad, I have 1 more question. 

I've fixed the supports of the columns in direction RX (Rotation about it's own axis), When I make them pinned they have errors due the RX. The columns can't rotate from the top anyways due to all other beams, is there a way robot can realize this? 

[Muhammed.OPERA]

Hi @Anonymous

The thing is why do you wanna make that?!!!

The default of the foundation case doesn't allow the column to rotate about it's own axes, don't it?

[Anonymous]

yeah you're correct, I just wanted to find out if robot would automatically recognize that the top side of the column has been fixed in rotation even if the bottom side was pinned. 

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

I just wanted to find out if robot would automatically recognize that the top side of the column has been fixed in rotation even if the bottom side was pinned. 

It actually does as by default all connections among bars are fixed but when you start defining releases for adjoining bars or make then as truss elements then you can make the column to rotate about their own axes even no releases are defined for the columns themselves.

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