In this paper, in order to identify the modal properties of a structure based on the ambient vibration monitoring, an innovative method for modal identification, called Hybrid Time and Frequency Domain Analysis, is described and a full scale test is presented. The method consists of frequency domain analysis for natural frequencies and modal shapes identification; and time domain analysis for the damping estimation. The methodology was tested in a 5 story steel frame structure constructed at the Disaster Prevent Research Institute, Kyoto University, Japan, using ambient vibration testing. The dynamic response was measured with simultaneous sensors in every floor, including ground. The modal shapes results were compared with the FEM and with previous results obtained from monitoring under forced vibration. For the damping estimation, free vibration results were compared with the ambient vibration test. The system identification obtained under ambient vibration tests are in very good agreement with the forced and free vibration tests and with the analytical results.
The aim of this study is to characterize the mechanical behavior of connections timber-to-timber joist hangers with specific nail fasteners. The methodology proposed by technical design standards is based on the hypothesis of an elastic and linear joint behavior. However, the local behavior of joint is semirigid characterized by the ductility of wood material in embedment and the non linear behavior of the nail fasteners in bending. Hence, in this study, the combination of a comprehensive experimental setup and a numerical approach is developed to analyze the evolution of the forces in the joint. Firstly, various tests are realized on specific nail fasteners, using different glulam species, in accordance with European test standards. They concern the withdrawal push-out test, the single plane shear and the yield bending moment. Besides, the adequacy of the methodology proposed by Eurocode 5 for dowel-type fasteners is discussed. Secondly, a similar investigation is carried out on a whole timber-to-timberjoint, with nailed tridimensional metal plates. Considering the hypothesis of a semi-rigid behavior of the joint, the stiffness of each fastener is identified in tension and shear slips. Finally, a finite element model is applied and discussed considering the fasteners represented by bi-directional mechanical springs. The stiffness of each spring is considered as the slip modulus of each fastener defined by tests. A semi-rigid formulation was adopted and the overall joint behavior is apprehended numerically.