3.7.11: Node Forces
For the design of connections between beam- and truss-elements the output of the "Node Forces"-component offers a god starting point.
In Fig 188.8.131.52 one can see the results for a node to which six beams with eccentricities connect. The first input on the left side is the model for which to retrieve the results. The node in question can be specified either via coordinate of node index.
The input-plug "Plane" lets the user define a plane of reference for the output directions "Dir" and the cross section forces "Fs" and moments "Ms". The latter applies only in case that the "Local?"-input receives 'False' - which is the default. If not specified the default reference plane is equivalent to the global coordinate system.
Via the "LCase"-input one can specify the load-case for which to retrieve the cross section forces.
If set to 'True' the "Local?"-input makes the output forces and moments in "Fs" and "Ms" refer to the local element coordinate system. This can be useful in some cases. Then however the sum of forces and moments and externa nodal loads does not add up to zero.
Fig 184.108.40.206: Cross section forces around a node with eccentric beams attached.
On the component's output-side one gets the list of beam- or truss-elements that connect to the node. The order of the unit-vectors in the "Dir"-List corresponds to that of the elements in "Elems". They point in the direction parallel to the elements but away from the node. By forming the dot-product between an element's local X-axis and the vector in the "Dir"-List one sees whether the element's starting- or end-point connects to a node.
The output "Fs" contains vectors of cross section forces Nx, Vy, and Vz - again in the order of output elements in "Elems". The moment vectors "Ms" - they contain Mx, My and Mz - refer to the position directly at the node. They get transformed to the element's reference line so beam eccentricities do not affect them. In this way they add up to zero (see fig. 220.127.116.11) in the absence of external nodal moment-loads.