Author(s)

A. K. Desai

Abstract

After the Bhuj earthquake event in 2001, earthquakes and seismic hazards are increasing as the Indian continent (Tectonic Plate) moves slowly towards the North-East Himalayan Mountain side. Now, because of the collision of two tectonic plates and due to a folding of the plate, the top crust is subjected to tension cracking. This is the main cause of earthquakes in the Asian region. The frequency of earthquake shocks from different epicenters is increasing as compared to previous shocks. The Indian government modified its seismic design code from I.S.: 1893– 1984 to I.S.: 1893–2002, for seismic safety in its newly designed buildings. However, problems do arise for old structures, as quite a large part of the Indian population resides in urban areas and some even in poorly constructed RCC buildings, with a seismic risk zone from Zone–III to Zone–IV (most dangerous). The only option remaining for local authorities for reduction of earthquake hazards and for increasing the safety of the urban population is for \“Seismic Retrofitting” of old structures. Three aspects are most important for prioritization of structures that need retrofitting 1. Structures of national importance, lifeline and critical facilities. 2. Multi-storied residential and commercial complex. 3. Only ground floor/ low rise residential building. Again, structural auditing for three aspects are required for priority of retrofitting - structures near to collapse, but can be refortified and require steel probe supporting; main structural components like beams and columns that require immediate retrofitting at some places; structures can be made safe following this old design code, but retrofitting is required from a new design code for higher level earthquakes. After mixing the above two auditing criteria, the availability of a

Keywords

effect of earthquake, retrofitting method, old and new building audit, seismic hazard, safety