“…where i s x , i s y are the linear stiffnesses of the strut with respect to the principal central axes of inertia x 0 -x 0 and y 0 -y 0 ; l s the length of the strut; 1 η x , 1 ζ x , 1 η y , 1 ζ y are transcendental functions that take into account compression in some struts and stretching in others, defined according to [2,8,14,15,19,20].…”