Iqbal 2006
This paper proposed a new version of the soft first story with elastoplastic isolation system. The concept of soft first story was explained in order to incorporate seismic isolation system. This enables separation the first story from the rest of the building. Isolation system provides the ductility and energy dissipation during an earthquake. Moreover, a number of systems having different shapes and arrangements were considered in this study and some arrangements showed that the soft first story provides effective protection against seismic forces while maintaining overall stability.
System Concept
The isolation system was composed of sliding bearings and steel dampers placed between the top of the first story and the rest of the superstructure. It allows for relative displacements between the adjacent elements while reducing the force transmitted to the upper level. Energy is dissipated through yielding of the steel elements.
The chosen arrangement should be stable in normal service condition and for wind loading; and should transfer the vertical load and keep minimum horizontal earthquake force transferred to the stories above.
The arrangement may consist of Teflon-stainless steel sliding bearings and steel dampers assembled in a single device.
Implementation
Problems with implementing the system on the ground floor include spaces have to be kept for movements, services have to be made flexible, underground water reservoir would need to be located above about the isolation level and additional attention to sub ground machinery and parking is necessary. Many of these special provisions can be avoided by installing the system on the top story.
Reference
Iqbal, A. (2006), “Soft First Story with Seismic Isolation System,” Proceeding New Zealand Society for Earthquake Engineering Conference, Napier, New Zealand, March 10-12.