Seismic Bifurcation for Response-control of Tall Building Structures

The response of a structure to a seismic activity depends on the characteristics of the structural system and the seismic activity. To improve the seismic response of a structural system, it is bifurcated into two subsystems: a flexible one, catering to the primary function/occupancy of the system and a stiff one, taking care of the lateral strength requirements and housing major services of the system. Low stiffness associated with large mass in the flexible subsystem results in shifting of natural periods of the system to zones of low seismic input energy. The difference in lateral stiffness of the two subsystems results in differential response, which is utilized by placing floor-level links between the two subsystems; these links absorb and dissipate a substantial part of seismic input energy leading to a minimal structural distress. Three types of structural systems, viz. conventional system, seismically bifurcated system with rigid links (SBS-RL) and seismically bifurcated system with damping links (SBS-DL), are analyzed for various parameters. The study shows that seismic bifurcation (SB) helps in controlling the seismic response of tall building structures. The study further shows that SB technique is useful in improving seismic performance of conventionally-designed existing structures by way of seismic retrofitting.