Design of Mass Isolated Structures with Consideration of Stability Constraints

Document Type : Research Article


International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran


Vertical mass isolation is one of the new techniques in the seismic design of
structures 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 main
feature of some new approaches in the seismic design of structures. Extra flexibility
helps to reduce earthquake-induced forces and accelerations in the building and
provides higher energy dissipation potential for the system (by creating large
relative deformations in the structure). Mass subsystem possesses low lateral
stiffness but carries the major part of the mass system. Stiffness subsystem, however,
controls the deformation of the mass subsystem and attributes with much higher
stiffness. In this paper, the aim is to find the limitation of the stability of a
soft structure and to obtain the maximum period available for a soft structure.
According to the studies, the most important obstruction in increasing the period
of the soft structure, assuming control of its deformation by connecting to the
stiff substructure, is to maintain the stability of the structure. In this paper, first, a
relationship has been presented to calculate the period of the structure in terms of
the stability factor that estimates the period of structure with good agreement by
analytical results. This paper deals with presenting a procedure for designing the
Mass Isolation System (MIS) with consideration of stability constraints. To this end,
the paper presents mathematical solutions to calculate the period of the structure
followed by proposing a design procedure of the soft substructure.