This is an issue I've been having with correctly modelling connection between two separate structures.
Beams shown in black are part of a structure.
Beam showing in red are a single 'droptube' which will be connected onto the main structure at 2 nodes: node 2 & 5.
In reality, the 'drop tube' is connected to the main structure using special clamps which transfer forces to the main structure but not any moments (for the sake of restraints in all degrees of freedom, let's assume it also transfers torsion to the main structure too). The moment due to force F would, of course de-couple at nodes 2 & 5 as translational forces. Simple to work this out on paper.
It is important to note that the black structure is one entity and the red drop tube is another separate entity. So how do we connect such structures together in STAAD.Pro to represent the above? This is where I have trouble with, as any moment releases at joints 2 or 5 will disjoint the two structures from themselves.
PS: having used a number structural analysis software packages in my time, a number of these packages allow for 'couple' or 'coupling' elements which consist of coincidental nodes whereby a 'couple' is connected between these nodes, with the correct releases. One of these coincidental nodes is associated the black structure and the other is for the red 'drop tube'.
Cnxn Reply.stdI've attached a file that shows two possible solutions. One involves using master and slave joints. This will produce some instabilities but the program compensates and solves correctly, at least in this case. The other one involves using dummy members with releases at the end. This may be easier to visualize what is going on.
I don't know if attaching that file worked or not. I'm going to hit "Post" and see what happens.
Answer Verified By: Dana Akbarinassab
Dear Tank,
Many thanks for your reply. I didn't know about the master/slave concept but it is indeed interesting and, as the results showed on the STAAD file provided, correctly implements what is needed.
SLAVE FZ MASTER 2 JOINT 9
Am I correct in understand that joint 9 will transfer only it's FZ component (in global direction) to joint 2? Is there a way for this force transfer to be in line with an element's local axis, as opposed to global?