Formation of an internally statically determinate truss

[GreatBlitz]

TL;DR

I am unable to understand how a given truss is internally statically determinate.

My professor taught me that a internally statically determinate truss is formed by having one basic truss - the triangular truss consisting of three joints and three members:

and then repeatedly adding two members and a joint:

So, it makes sense why this is a statically determinate truss:

However, I don't understand how this can be a statically determinate truss under the same reasoning:

Can someone can help?

 

[Dr.D]

Do you not see triangles in the last figure?

 

[GreatBlitz]

Do you not see triangles in the last figure?

The truss in the third figure can be easily formed by starting with one triangle and then successively adding two members and a joint between them (first and second figures). However, I don't see how this can be done with the last figure, even if it is made of triangles.

 

[Dr.D]

Why not build the cluster of triangles on the left side, then build the cluster of triangles on the right, and finally add one pin and one member to joint the two clusters?

 

[GreatBlitz]

So if what you

Do you not see triangles in the last figure?

So if I understand you correctly, what you're saying is that all trusses made of solely triangles are internally statically determinate. Then can you explain why this is (internally) statically determinate?

 

[Dr.D]

I never said anything about being statically determinate or not, and certainly not about your last figure. You are moving the goal posts here.

Being statically determinant or not is, to some degree, dependent upon how the frame is loaded. You last figure may not be statically determinant if the extreme left and right nodes are not externally loaded.