Question:
How can I model double members in RSTAB 9, such as those in a telescopic connection?
Answer:
The nested components of a telescopic boom of a construction machine, for example, transport their forces mechanically between the components.
This special force transfer can be solved in RSTAB 9 as follows:
► Image | Modeling Plug Connection https://www.dlubal.com/en/img/051111
A characteristic plug connection like the one shown in the sketch consists of four members. Two members (Members 2 and 4) lie on top of each other in the overlap area.
You can create superimposed members using nodal releases. For this, you have to define a nodal release at Node 2 which releases Member 1 and Member 2. The nodal release creates Node 5, which acts as the end node of Member 1 and the start node of Member 2. Member 1 and Member 2 are rigidly connected to each other.
► Image | Nodal Release at Node 2 https://www.dlubal.com/en/img/051113
Now, you can define the overlapping Member 4 between Node 2 and Node 3. It is also necessary to define a nodal release at Node 3, which releases Member 3 and Member 4. The nodal release creates Node 6, which acts as the end node of Member 4 and the start node of Member 3. Member 3 and Member 4 are rigidly connected to each other.
► Image | Nodal Release at Node 3 https://www.dlubal.com/en/img/051114
To ensure that the structural force is only transported via a force pair at the ends of the overlapping members, constraint conditions between Nodes 2 and 5, as well as Nodes 3 and 6, must be defined in the nodal releases as a nodal release type.
► Image | Nodal Release Type of Nodal Release at Node 2 https://www.dlubal.com/en/img/051115
► Image | Nodal Release Type of Nodal Release at Node 3 https://www.dlubal.com/en/img/051116
A moment hinge in the nodal releases between Nodes 2 and 5 as well as Nodes 3 and 6 should ensure that the bending moment load between the red members (Member 1 and Member 2) and the green member (Member 3 and Member 4) is transferred by the force couple at the ends of the overlapping members.
An axial force hinge in the nodal release between Nodes 3 and 6 is intended to ensure that an axial force load is only transferred between the green and red continuous members for the planned fixation.
