Exploring Divergence and Deviations of Seismic Performance of Set-Back Structures

The Indian subcontinent comes under the category of the world’s most disaster prone areas with a population of more than 121 crores. The geographical statistics of India show that about 34% of the land is susceptible to earthquake. Further classification of the earthquake prone land shows that 12% of land is prone to very severe earthquake, 18% of land is prone to severe earthquake and 25% of land is prone to damageable earthquake. The effects of some of the worst earthquake which took place in various countries are defined below which emphasis on the events which are of interest to structural and civil engineers. The 1971 San Fernando Earthquake occurred in early morning of February 9 in the foot hills of the San Gabriel Mountains in California. The surprising thrust earthquake had a moment magnitude of 6.5 or 6.7 and had a maximum Mercalli Intensity of XI (Extreme). The Olive View Hospital, which nearly collapsed due to excessive deformation in the 1st two storeys during this earthquake and was subsequently demolished due to discontinued shear walls. The Turkey Earthquake: The earthquake that struck in the northern Turkish region of Kocaeli the strong ground shaking produced by this earthquake was not usually high, reaching around 40% of the acceleration of gravity in the epicentral region, but the quake was of long duration 45 seconds so the shaking was significant factor in the degree of structural damage sustained. The majority of the housing and commercial buildings built in Turkey had soft storeys at the first-floor level which were frequently used for commercial purposes. These storeys were normally enclosed with glass windows as a replacement for of brick infill walls so as to be used as showrooms. As many as 115,000 of these building some engineered, some not were unable to survive the strong ground shaking and were either badly smashed or collapsed completely. A massive earthquake of magnitude ML=6.9 on Richter scale occurred on the morning of 51st Republic Day of India (January 26, 2001, Friday) at 08:46am (Indian standard time) as reported by Indian Meteorological Department (IMD), New Delhi. The earthquake is subsequently referred to as Bhuj earthquake. The earthquake ranks as one of the most destructive events recorded so far in India in terms of death toll, damage to infrastructure and devastation in the last 50 years. RCC multi-storey building in India, for the first time, has been subjected to a strong ground motion shaking in Bhuj earthquake. It has been observed that the principal reasons of failure may be accounted to soft storey, floating column (infill walls that are present in upper floors are discontinued in the lower floor), mass irregularities, poor quality of construction material and faulty construction practices, stiffness and strength irregularity, inconsistent earthquake response, soil and foundation effects and pounding of adjacent structures.