Elastic Modulus E = strain stress = ( )( )Lδ
AF = Aδ FL
This equation can be re-arranged to give:
F = δ L
hence when δ =1.0 (i.e. unit displacement) then the axial stiffness k (= F) = L
7.2.1 Beam Elements with Two Degrees−of−Freedom Consider a ‘beam element’ of length L, Young’s Modulus E and cross-sectional area A which is subject to axial forces F1 and F2 at the end nodes A and B as shown in Figure 7.2.