Multiple Cables supporting a point load

[Anonymous]

Hi,

I'm applying a point load to a cable and not happy with the amount of deflection/capacity as it won't suit the application (mesh reinforcement for a small gate/fence)

I want to add a second set of cables to have it act as a grid in catenary but I get a 'separate structure', a displacement error for the new cables and it results in it not picking up any load.

How do you model several cables to allow for load-share?

[Krzysztof_Wasik]

Hi @Anonymous 

Share file for verification

[Anonymous]

Hi, Have attached files.

'Barrier Load' is the simple cable, 'Impulse Catenary' is the one which is producing the errors.
Thanks

[Krzysztof_Wasik]

HI @Anonymous 

I would suggest the following solution

Divide long cable in two parts. 

Define initial cable prestress force (10 kN will work)

In load case parameters activate large displacements and matrix update after each iteration.

Attached modified file. 

See this forum thread for more information.

[Anonymous]

Thank you. Regarding prestress, It will be a simple round bar welded to the frame so I'm not anticipating any prestress on the cable at the time of install. Is there a way of modelling bar properties or do you just define a nominal reduction in length to get the initial 'tension'

[Krzysztof_Wasik]

Hi @Anonymous 

I have verified your model once again.

In Robot Structural Analysis, workflow for cables, needs assembly load case definition. Then in next load cases external loads should be defined. Defining external force in assembly case is incorrect. Previous model was not good. Sorry for too quick answer.

Assembly load case usually includes prestress forces and structure self-weight.

External forces are balanced by cable tension, acting on deformed structure geometry. Cable elements does not have bending stiffness. 

So I would modify your model by adding assembly load case (it can be empty load but I would suggest add cables self weight to this case) with case number 1. To obtain any cable stiffness (when cable self weight is not defined) I would apply minimal tension force (0,0001 kN). Then external force can be defined in next load cases (load case 5).

If you are using welded bars with bending stiffness (not cables) use bar elements with real section definition and large displacement analysis (when bars are flexible).

See corrected model version.