Issue 47

A. Namdar et alii, Frattura ed Integrità Strutturale, 47 (2019) 451-458; DOI: 10.3221/IGF-ESIS.47.35 454 Figure 4 : Acceleration history of earthquake used in numerical analysis [23]. T HEORETICAL CONCEPT timber beam of homogeneous, isotropic and linearly elastic material with modulus of elasticity E and Poisson ratio ν , and constant cross section is installed in single span of timber frame, has been numerically investigated. The model has been considered under internal and external dynamic loading. Considering a static problem, during the action of internal and external forces. The sum of all the virtual work is: 0 W    (1) when all the external and internal forces are derived from a potential function U, which is a function of the coordinates of the system of particles, W U      (2) The virtual work leads to establish the principle of stationary potential energy 0 U   (3) The above formulation may be extended to the dynamical problem of a system when it is subjected to time-dependent applied forces and geometrical constraints. The principal virtual work for the dynamical problem is given by: 2 2 1 1 0 t t t t Tdt Wdt        (4) where T is the kinetic energy of the system. The state of the strain at a point of the body is defined by six components of strain ( , , , , ,  x y z yz zx xy       ). In small displacement theory, the strain-displacement relationship are given as follows [24]: x u x     (5) y v y     (6) A