Instability type 1 and 2 in frame/cable structure

[mailingbot]

Hi,

I am just a begginner in autodesk robot and I am an architect not an structural engineer so I could have made mistakes.

I am trying to analyze a 3d structure consisting of timber frames with additional wire support. 

I am using a script to transfer the shape from grasshopper to robot.

I am getting instabilities at all the positions of wires.

The way I define wires might not be right as I am not using cables from robot.

I just used a steel element with hinges on both sides. This shouldn;t matter in the instabilities I think as I should get it working if I use steel bars instead, but it isn't working.

I am attaching a file in robot and also the design concept of the trusss that show s the idea behind it

[Rafacascudo]

Delete releases for "Wire section" and " section verticals". Set the "Wire section" bars to tension only ( Menu/geometry/additional atributes/Advanced bar properties)

Set non linear paramenters for each load case and combination to... see below , tick "matrix update after each iteration"

you should look carefully to this structure model as not all "Wire section" bars are in tension

[mailingbot]

Thank you. After doing these steps I do not have instability errors any more. 

I sometimes get "incorrect use of a release for a truss member" - Only non linear releases for UX are allowed...

It happens when I export from grasshopper to robot without any releases on verticals and wires. It does not hapen when I export with releases and I delete them. As I want to do many iteration with sligthly different shapes I am wondering why is this happening?

Also I am wondering about your statement that not all wires are in tension. The situation in the back is complicated and the wires are there only for aesthetic purposes, as the balcony columns apear here. Is this the area were you meant that the wire is not working?

[Rafacascudo]

bars assigned with " tension only" property get Fx=N/A on "forces" table , when they " failed" to get in tension.

On this table window , select the lines that have N/A value for Fx and these bars will also be selected on the graphic window.

As this is a nonlinear analysis, only " self weight " case makes sense . For your cases with wind and snow ,etc you have at least to add the " self weight" to the load case or create a combination including the self weight load case.

[mailingbot]

I am using ULS load cases with dominant wind or snow. Each time I am also adding the self weight with coefficient of 1.35.

So I think the ULS combinations should be fine?

I just discovered that the self weight had roof weight but didnt have the selfweight robot component applied

Thats what I got after trying to select those with F/x = N/A, I dont really understand what is this,

but i still get the same error with incorrect releases for truss member. Do I have a truss memeber anyway? I am lost...

[mailingbot]

I think after reading a bit through autodesk help I understand more.

SO what I understood is when I define the bars to be tension only, they become truss bars - and the program has already a built in definiton for it releases. I do no need to define them and if I define them I cause problems (The incorrect use of releases for a trusss member).

But I do not understand why I cannot define hinge at the end of vertical timber elements. I want to join them with wires - but the structure works only if I take away all releases.

With hinge at the end of verticals I get instability.

[Rafacascudo]

You don´t need to define a "hinge" at the end of the vertical bars because they´re connected to truss bars !!!! There will not be moments at this node!

[mailingbot]

Thank You for this answer. I am not really good at structures...

Then this means that my structure probably works. Thanks again!