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Vertical mass isolation approach is a new technique in which an individual structure is divided into two distinct subsystems and each possesses different characteristics. Such two subsystems–mass and stiff subsystems– are interconnected with passive dampers in vertical layers at the height of the frame. The primary task of such passive devices is to reduce the structure's seismic reactions by dissipating more of the seismic forces, as well as regulating the amount of structure displacement. In this paper, two models of stiff subsystem placement are introduced, the inner stiff subsystem(ISS) and the outer stiff subsystem(OSS). Structural models are introduced in two types of five and ten-story for both ISS and OSS systems. Metallic dampers were used as fuses to reconnect the isolated structures. For all models under seven distinct earthquake ground motions, nonlinear time history analyses were executed. The findings related to base shear forces, the shape of plastic hinges in structural components, the responses of roof acceleration, and the dampers’ hysteresis behavior are studied. Based on the numerical data, the ISS system has a minor advantage over the OSS system in improving the structure's seismic efficiency and reducing seismic reactions.

A linked column frame (LCF) is a seismic-load-resisting system with ductile behaviour. In this system, the link beam, operating as a shear fuse, reduces or eliminates damage to other components of ...

Effects of earthquakes on tunnels and underground structures can be investigated in two aspects: longitudinal tunnel behavior and Racking tunnel behavior. In this paper only the effects of the earthquake on tunnel section (racking behavior) is studied by modeling in plane-strain condition. Thus the obtained reduction factor is the tunnel racking reduction factor. In this paper, by performing a pushover analysis and using the proposed methods of Wang (Seismic design of tunnels: a state-of-the-art approach, Parsons Brinckerhoff Quade & Douglas, Inc., New York, 1993) and Hashash et al. (Tunn Undergr Space Technol 16:247–293, 2001) in determination of the tunnel racking deformation and proposing a trial and error pattern, the performance point of the tunnels in the earthquake is determined considering nonlinear behavior of the tunnel lining. In the next step, by using the pushover curve and applying the existing equations of calculating reduction factor in the structures and considering the soil-structure interaction, tunnel racking reduction factor (TRRF) are estimated. Finally, three nonlinear dynamic analyses consistent with the site are performed using finite element software. Comparison between the modified forces by using the reduction factor in the linear static analyses and the forces obtained by applying earthquake records in the nonlinear time history analyses, shows the good accuracy of the obtained reduction factors. The studies also show that implementing linear static analyses without tunnel racking reduction factor leads to very conservative results of lining force in tunnel. Since the TRRF values are sensitive to the soil type and overburden depth, the sensitivity analysis is performed for the overburden depths of 5 and 20 m and two soil types to achieve a more comprehensive result.

Stress reduction factor, λ, is a dimensionless coefficient in two-dimensional (2D) analysis based on convergence confinement method (CCM) of tunnel which represents stress relaxation in the tunnel walls at different excavation steps. The aim of this paper is to look into the influencing factors on parameter λ around the tunnel walls using finite difference code in order to improve the accuracy of the CCM. For this purpose, four different ground types with various tunnel radii, depths and cross section shapes are considered. Finally, the 2D analysis using uniform and variable stress reduction factors determined in this paper is compared with the 3D analysis of the tunnel. The results of this study enhance our understanding of the role of geometrical and soil material parameters of tunnel on stress relaxation around tunnel walls. The tunnel depth, soil type and tunnel shape have great influence on λ. Variable stress reduction factor enables the convergence–confinement method to predict the realistic behavior of third dimension of the tunnel and can also be used as the best alternative to 3D models.