Abstract
School buildings being a critical social infrastructure, assessment of their seismic behaviour is of utmost importance in ensuring safe schooling facilities in locations of high seismicity. This study presents two important aspects in analysing any existing building stock for seismic behaviour: the development of an appropriate taxonomy system and an appropriate analytical method to conduct fragility assessment. A detailed desk study of existing schools’ databases and tailored field investigation in Guwahati, Assam, situated in India’s highest seismic zone, reveal that the majority of school buildings can be categorised within the confined masonry (CM) typology. This study discusses first, the addition to the World Bank promoted Global Library of School Infrastructure taxonomy of the specific category relating to CM as to include the buildings under study, which are non-engineered CM buildings with flexible roofs. Identifying the density of confinement and quality of connections as critical parameters for the seismic response of these buildings, varying seismic design levels are defined in relation to these indicators. Secondly, the paper presents an approach for carrying out nonlinear static pushover analysis of these buildings with flexible diaphragms and elaborates on the criteria adopted for determining the performance drift limits in buildings with varying levels of seismic design. Numerical analysis for the capacity assessment of selected index buildings is carried out using a commercial software that enables nonlinear extreme loading analysis. Different failure mechanisms as a function of the level of confinement are identified and the performance range for three damage states for three index buildings is obtained by using the N2 method. The study shows the influence of both choices of performance indicators and intensity measure on the resulting fragility functions. Given the consistency of the educational building stock in Guwahati, the results can be used for investment on retrofit decision making at regional level.
Highlights
1.1 BackgroundConfined masonry (CM) is a structural system formed of unreinforced masonry panels confined by lightly reinforced concrete elements at all intersections and periphery
The study recognizes them as a variant of confined masonry typology and proceeds to assess their available seismic capacity due to the presence of reinforced concrete (RC) confining elements
The level of confinement density, a critical factor determining the seismic performance of these buildings, is incorporated into the taxonomy through the definition of seismic design levels, by reference to international Guidelines
Summary
Confined masonry (CM) is a structural system formed of unreinforced masonry panels confined by lightly reinforced concrete elements at all intersections and periphery This typology is found to have superior seismic performance compared to unreinforced masonry (Tomaževic and Weiss 2010; Chourasia et al 2016), mainly due to improved ductility provided by the confining elements. First reported in use after the 1908 Messina earthquake, Italy, this construction practice has been in existence in Chile and Columbia since 1930′s and in Mexico since 1940′s (Brzev and Perez-Gavilan 2014). Observation after multiple earthquakes in Chile and Peru have highlighted the superior performance of CM structurers compared to other forms of masonry construction, while signalling limitations and failure mechanisms of this typology under seismic action (Meli et al 2011; Astroza et al 2012). Guidelines for the construction of CM buildings are available internationally and in countries where this construction practice is well established and encouraged (NCh2123 1997; NTC-M 2004; Meli et al 2011)
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