Initial Solution for Designing a Soft Substructure in a Mass Isolation System with Consideration of Stability Constraints

The new techniques in seismic design of structures are usually attributed to high damping ratios. Mass isolation of structures is one of the new techniques in seismic design of structures that focuses on the mass of the structure as the main target for seismic isolation and reducing earthquake effects on buildings. Mass Isolation System (MIS) consists of two stiff and soft substructures connected by a viscous damper. The mass subsystem comprises the main mass of the structure, which is attached to a frame with a low stiffness by a separation mechanism at the height of the structure including viscous dampers to a stiffness subsystem consisting of a moment or braced frame system with great stiffness. In this paper, the aim is to present a simple preliminary design method based on the normalized pushover curve. The most important problems for increasing the period of the soft structure are deformation and structural stability. This paper presents a preliminary design solution for a soft substructure of the Mass Isolation System (MIS) with consideration of stability constraints. To this end, the paper presents mathematical relationships to calculate the period of the structure followed by proposing a simple solution for the design of the soft substructure.