Issue 47

A. Namdar et alii, Frattura ed Integrità Strutturale, 47 (2019) 451-458; DOI: 10.3221/IGF-ESIS.47.35 456 consideration of models response, it has been observed that, the elastic displacement of timber beam with the same stiffness, but with nonlinear deformation, have been occurred. The inertia is developed in a timber frame during the seismic loading, producing shear, moment and torsional excitation. However, these loads cause hysteretic displacement variation in all timber frame components, with respect to flexibility level of timber frame. The seismic wave propagation into the timber frame, causes hysteretic displacement. The seismic energy dissipation significantly affects the overall timber frame seismic behavior. Considering the structural inertia, the kinematic interaction, results in stiff beam elements, which cause timber frame motions to deviate from free-field motion. The structure and foundation inertia, consist of the relative foundation-free field displacements. The flexural, axial and shearing nonlinear deformations of timber frame elements that occur, due to seismic load mechanism, are applied on model. These deformations significantly change the model behavior, especially in terms of damping, inertial interaction and energy dissipation. The strain-displacement of timber frame is a representation of the nonlinear model behavior, and illustrates kinematic interaction of beam, which solve kinematic interaction problem beyond the ability of most commercial software. ABAQUS is able to show kinematic interaction, drawing cyclic graphs. The strain-displacement curve and nonlinear deformation of timber beam are dependent on the stiffness and geometry. The high strain-displacement have been observed in both models. The shape of strain-displacement curve are shown. The shear strain is developed with reduction of timber length [Figs. 7-8]. Figure 7 : Strain Vs displacement on timber beam with 3.3 (m) length, model-1. Figure 8 : Strain Vs displacement on timber beam with 1.8 (m) length, model-2. The load-strain curve describes the stiffness and damping characteristics of timber frame and beam-column interaction as well. Two different strain energies are developed in the models 1 and 2. The morphology of timber beams is correlated to different strain energy magnitude and shape for, each location and timber beams. From the seismic design point of view in a force-displacement diagram, the strain energy stored in the timber beam has been illustrated. The load-strain mechanism is part of the strain energy corresponding to the linear elastic response. For timber beam it is responding in the nonlinear range of loading, unloading and reloading. The energy dissipation causes nonlinear deformation and displacement. Therefore, the hysteresis loop of load-strain, illustrates the strain energy dissipation process. A flexibility of timber beam of 3.3 (m) reached at failure displacement with lower elastic strain energy, is reduced in this model by the damping ratio. The structural damping ratio will depend on elemental damping ratio and on the stiffness of the models. The relationship between the work done by seismic force and the elastic strain energy in one cycle of loading, unloading and reloading are shown in the graphs. The percentage of the seismic load carried out by beam and columns is affected to flexibility of frame. This process leads to develop different load-strain curve for each model. The magnitude and the direction of load sharing between beam and columns in each model, have specific characteristics, depending on timber frame span [Figs. 9-10]. In this numerical analysis, only one types of wood has been used in timber frame simulation. But it is indicated that [25], the strength of materials has significant effect on load sharing. The load sharing process effects to yielding of the lower strength and stiffness, resulting in change load transmission.