SEISMIC FRAGILITY ANALYSIS OF UNREINFORCED STONE MASONRY STRUCTURE: A CASE STUDY OF TRADITIONAL BUILDING AT GHANDRUK VILLAGE

Abstract

URM buildings located in mountain and hill areas of Nepal are typically constructed using boulders, rubble stones or dressed/semi-dressed stones using mud mortar, or in some cases using dry stacked masonry units. Such buildings are constructed based on traditional techniques using locally available material and roofing technique. For centuries, unreinforced stone masonry, utilizing stone as the primary construction material with or without the use of mud mortar, has been a cornerstone of Nepalese architecture. This traditional building technique, while culturally significant, has been particularly susceptible to the catastrophic impacts of seismic activities. Despite this, stone masonry buildings remain the dominant construction method due to economic constraints in rural Nepal. This study focuses on seismic performance assessment of a stone masonry buildings constructed with mud mortar (SMM) representing typical Nepalese URM constructions. The reconnaissance survey was carried out in a total of 61 buildings in major settlement of Ghandruk village. The mechanical properties of the masonry were identified through in-situ tests, including the Rebound Hammer test, Penetrometer test and Pendulum Hammer test. A nonlinear three-dimensional finite element model of typical URM structure was developed and analyzed in DIANA FEA. The seismic performance of structure was evaluated using nonlinear pushover analysis (NLPA), which indicated a base shear capacity of 554.023 KN at a target drift of 1.79%. Nonlinear time history analysis (NLTHA), under several real-time earthquake ground motion was further studied to assess structural fragility. The fragility curve derived from IDA shows the probability of exceedance for IO, LS and CP damage states as 100%, 89% and 63% respectively, at a peak ground acceleration (PGA) of 0.3g. These results highlight the structure’s high vulnerability, exhibiting high risk of building collapse at strong ground motion intensity.