Mohammad Boujary - International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
Mansour Ziyaeifar - International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran

Vertical mass isolation is one of the new techniques in the seismic design ofstructures that consists of two stiff and soft substructures connected by viscous dampers.Adding to the flexibility and energy dissipation potential of the system is the mainfeature of some new approaches in the seismic design of structures. Extra flexibilityhelps to reduce earthquake-induced forces and accelerations in the building andprovides higher energy dissipation potential for the system (by creating largerelative deformations in the structure). Mass subsystem possesses low lateralstiffness but carries the major part of the mass system. Stiffness subsystem, however,controls the deformation of the mass subsystem and attributes with much higherstiffness. In this paper, the aim is to find the limitation of the stability of asoft structure and to obtain the maximum period available for a soft structure.According to the studies, the most important obstruction in increasing the periodof the soft structure, assuming control of its deformation by connecting to thestiff substructure, is to maintain the stability of the structure. In this paper, first, arelationship has been presented to calculate the period of the structure in terms ofthe stability factor that estimates the period of structure with good agreement byanalytical results. This paper deals with presenting a procedure for designing theMass Isolation System (MIS) with consideration of stability constraints. To this end,the paper presents mathematical solutions to calculate the period of the structurefollowed by proposing a design procedure of the soft substructure.

Mass isolation, Structural stability, P-Delta effect, Collapse prevention