2011 Sikkim Earthquake at Eastern Himalayas: Lessons learnt from performance of structures

Abstract

On 18 September 2011, all the Indian states and countries surrounding Sikkim witnessed a devastating moderate earthquake of magnitude 6.9 (Mw). Originating in Sikkim–Nepal border with an intensity of VI+ in MSK scale, this earthquake caused collapse of both unreinforced masonry buildings, heritage structures and framed structures followed by landslides and mud slides at various places of Sikkim. Significant damages have been observed in relatively new framed structures mainly in Government buildings, thick masonry structures, while, the older wooden frame (ekra) non-engineered structures performed well during the earthquake. Further, it is noteworthy that government buildings suffered more than private ones and damages were observed more in newer framed structures than older ones. Analysis of the damages identify lateral spreading of slope, pounding of buildings, out-of-plane rotation, generation of structural cracks, plastic hinge formation at column capitals and damage of infill wall material as predominant damage features. A few remedial measures are also attempted to be mentioned with future need of research and application. It has been felt to create awareness regarding these issues and is the need of the hour.