00:02
So to identify the zero force members in this diagram here, we're going to look at each of the different nodes and the trusses, node by node.
00:13
So we're going to start up here at node c, because this is relatively simple.
00:18
We can see that we've got here a joint with no external load and two non -parallel trusses.
00:25
And so we automatically know that the only way to achieve equilibrium at node c is to have zero force in each of these two trusses here.
00:35
So our zero force trusses must include bc and cd.
00:42
And so we can now look at the remaining four nodes ignoring these two trusses and that node there.
00:48
So next up, we're going to think about node d.
00:51
So this is the only node that has an applied external force.
00:55
So looking at node d, thinking firstly about the vertical equilibrium, we can see that that external force acting downwards has to be balanced by a force from trust bd.
01:08
So trust bd is not zero force, it's got forces acting on it to balance this that will then act on node b.
01:16
Thinking about the forces on node d horizontally now, we can see that the only trust that could be providing any force is d .e.
01:26
And since we're in equilibrium, we can't have an unopposed force.
01:28
And so de must also be a zero -force trust.
01:37
So we can add that to our list.
01:39
De is zero -force...