The damage that can occur to structures by way of deformation in bending under the excitation of random forces (referred to hereafter as ‘bending structures') is considered a local state due to the harm caused by cracks. Its effects on the behaviour of the structure are discussed as discontinuity phenomena. For the simulation of such discontinuities, the bilinear stiffness reduction function, which results in asymmetrical behaviour of a damaged member when loaded in opposite directions, has been defined together with a corresponding crack index. For different damage scenarios, the effect of the non-linear behaviour of affected members has been investigated according to which damaged members can be identified by means of a crack index. The proposed damage identification method is not hampered by the existence of any kind of noise. The effectiveness and accuracy of the proposed method have been examined by applying a ‘closed-loop solution' to a six- and an eight-storey bending structure, using in each case an analytical model and different pre-defined damage scenarios. Taking into account these scenarios, several bilinear stiffness reduction functions were assumed not only for the column stiffness coefficient of one or more theoretically damaged storeys of the investigated structure, but also for the beam stiffness coefficient corresponding to one or more such storeys.

In general terms, the aim of "System Identification" is to determine the dynamic characteristics of mechanical systems. These characteristics include both frequency characteristics (frequencies, mode shapes, and damping ratios) and the system's characteristic matrices (the matrices of mass, viscous damping, stiffness, Coulomb damping or coefficients of friction, and the Duffing stiffness). In such fields as "Damage Detection" in structures, identification of the system's characteristic matrices is of the same importance as the identification of the frequency characteristics, or even more so, by identifying these matrices, the intended goals in Damage Detection can be achieved. In line with such identification, a new algorithm for the system identification of shear structures is presented in the paper. Taking into account the fundamental and significant effect of noise attenuation in boosting the levels of precision and the correctness of system identification, this method helps to achieve noise attenuation by trimming noisy records in the frequency domain, in parallel with the identification of the structural system. The efficiency and precision of the method have been examined through the application of a "closed loop solution" to a five storey model of shear structure.

<p>In this study, the function and application of seismic isolation system through lead rubber bearing isolator (LRB) in near-fault earthquakes are compared with fixed-base structures. As a result of their high frequency content, near-fault earthquakes impose huge energy on structures and cause severe damages. One of the appropriate solutions for this issue is the use of LRB which decreases the amount of imposed energy on structures. To improve the function of isolated structures under the near-fault earthquakes, isolators are designed in a way to tolerate the vertical component of earthquakes. To this purpose, we limit the displacements due to the horizontal movements of isolator through Gap spring which acts as a retaining wall and prevent shocks to other buildings. Moreover, this approach decreases the vertical movements of isolators and indirectly improves their behavior. In the current study, three buildings with four, eight, and 12 floors (with and without gap spring) were included. Isolators were manually designed in accordance with AASHTO-LRB regulations and the behaviors of both isolators and buildings are considered non-linear. Then we analyzed and compared the amount of energy, displacement, and acceleration of structure at the center of roof. The results indicated a significant decrease in the results of base shear, the acceleration of roof center, floors drift and energy imposed on the structure in the isolated system in comparison with the fixed-base structure.</p>

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During recent decades, tunnels construction in urban environments has been recognized as a useful factor in improving transportation situation in cities. Construction of underground structures like tunnels has a direct impact on the above-ground structures. The most important impacts are soil crust movement of the structure movement), acceleration change of the earthquake on structures, and land subsidence. The present research aims at seismic evaluation of the effect of soil type in land subsidence and effective mobility time in tunneling projects. For this purpose, two different soil types are chosen to model and assess factors using numerical methods. The outcome of this research concludes that tunneling changes in the dominant frequency record if these changes reach to the extent that structure frequency equals to record frequency, resonance phenomenon happens.