The figure shows the free body diagram of the tube near the free end B. The load on top of the tube is P which equals 30 kilo newtons directed vertically downwards. The reaction force on member 2 is F subscript 2 directed vertically downwards. The reaction force at the base of the tube is F subscript 1 directed vertically downwards.

Force-deformation relationships will be written for each of the axial components. The internal force in an axial member will be assumed to be tension.

For tube (1), the force-deformation relationship can be written as:

δ1=F1L1A1E1

and for core (2):

δ2=F2L2A2E2