A shell structure supports its self and a frame structure does not support it self.
frame structure
It is a shell because the structure is with a hallow, curved shape
frame structure
A tent is a frame structure
It is a shell structure so that it can hold stuff.
Shell structure
frame
my toes
There is no relation between space truss and shell structure, a shell structure cannot behave like space truss, the distribution of force in a shell structure behave like a beam or a plate, and space truss behave more like a roof frame
solid structure
it is a frame sturctures
a teepee is a frame structre