42. Solving for pinned member actions

Questions and discussion for this lecture live here. Fire away by hitting Reply below :fire:

What is the use of pinDoF?
The use of pinDoF is justified when ONLY 2 members join at a node AND both members are pinned at this node. Then the pinDoF is absolutely required to provide a rotation reference to this node. If not, the program cannot solve the problem.
We can get the same result by eliminating pinDoF and providing a pin only at one member. This effect is the same as 2 pin plus pinDoF. The node rotate with only one member (no transmission of moment between the 2 members).
Also, when adding a member to the node (3 members connecting to the same node) with pinDoF, it is not possible to free one member and get the 2 others rigidly connected. It is however possible using a pin only on the member that we want the end simply supported.
The rule must be: the number of pinned connection must the number of member - 1. Keeping at least 1 rigid connection with a member.