RESPONSE OF BASE-ISOLATED BUILDINGS TO WIND LOADING

Abstract

In the recent years, base-isolation has emerged as one of the feasible techniques in the design of earthquake- resistant structures. Wide acceptability of this technique has led to adoption of Base-isolation systems to increasingly taller buildings. The development of modern materials and progressive techniques in civil engineering has paved the way towards a new generation of structures, that are taller, slender, flexible, low in damping and light in weight. Structures embodying such features respond readily to dynamic loads and exhibit a high degree of sensitivity to wind. The insertion of Base-isolation system considerably increases the horizontal flexibility of the structure. The reduction in the fundamental natural frequency shifts the resonance response away from the high-energy portion of the earthquake but moves it into the high-energy zone of the wind spectrum because as per the characteristics of wind spectrum the high energy in wind almost invariably exists at lower frequencies. Due to increased lateral flexibility, modern tall base-isolated buildings are extremely wind-sensitive and may oscillate excessively under strong windstorms. The level of these oscillations may not be significant enough to cause structural damage but may cause discomfort to the occupants. In the early stages of development of seismic isolation, prevention of collapse of the structure was the primary goal. However, more recently, other additional considerations like comfort of occupants, functionality of important buildings during and after earthquakes, protection to non-structural elements and contents have exerted an increasingly important influence; therefore the concept of no-collapse may now be too restrictive.