Seismic evaluation and retrofit of masonry school buildings in the Himalayan state of Uttrakhand, India

Abstract

Himalayan region is one of the most seismic areas of the world. However, similar to many other seismically active regions of the world, there is a large numbers of unreinforced masonry buildings, most of which have not been designed for seismic loads. Recent Earthquakes have shown that such buildings are highly vulnerable to earthquakes. Retrofitting of these masonry buildings is the most perceived issue of the present times. The most common method of strengthening of masonry buildings are surface treatment, grout and epoxy injections, micro concrete in splint and bandage and strengthening of existing members by FRP or RC jacketing. Many times these techniques are used as out of box solutions as analysis of masonry structures is a complex task. Unreinforced masonry walls are very weak in out-of-plane bending due to lack of tensile strength. These are generally not capable of bearing out-of-plane bending moment, even resulting from their own inertia. These walls act as shear-walls in their in-plane action and possess sufficient in-plane strength, if not weakened by too many openings. While adopting strategy of retrofitting for this building, care has been taken to ensure integral box action by suitable means. Most of the government school buildings in rural areas of North India are constructed of unreinforced masonry. These school buildings are socially important structures and most vulnerable in region of high level seismicity. As part of collaboration between the Indian Institute of Technology Roorkee (IITR) and Nanyang Technological University (NTU) Singapore, supported by Temasek Foundation, Singapore, ten schools have been retrofitted in five cities of India. In this paper a case study of four schools in Uttrakhand state has been presented. All the school buildings are evaluated for expected seismic hazard, as per Indian code and retrofit design has been implemented with welded wire mesh and micro concrete in form of horizontal bandage, and vertical splints at corners and junctions of walls. The paper presents the analysis and design methodology along with implementation issues.