Proceedings of IOE Graduate Conference, 2019-Summer Peer Reviewed Year: 2019 Month: May Volume: 6 ISSN: 2350-8914 (Online), 2350-8906 (Print) Seismic Risk Assessment of Vertically Irregular Buildings Latip Kumar Sharma a , Kamal Bahadur Thapa b a, b Department of Civil Engineering, Pulchowk Campus, IOE, Tribhuvan University, Nepal Corresponding Email: a 073msst110@ioe.edu.np, b kamal.thapa@ioe.edu.np Abstract The construction of the vertically irregular buildings are almost inevitable due to the functional as well as aesthetic requirements. However, Post-Earthquake damage assessment shows that the structural irregularity plays vital role in the seismic performance of the buildings. Sudden change in the strength, stiffness as well as load path discontinuity increase the seismic demand of the building which increase the vulnerability of the buildings. Seismic risk assessment in certain geographical area requires the fragility model of the different archetype of the buildings. In this research, a humble effort is made to comprehend the analytic seismic fragility estimate of the existing types of the vertically irregular reinforced concrete buildings in Nepal. Keywords Verical Irregularity, Seismic risk, Reinforced Concrete, Pushover Curve, IDA curves, Fragility curves 1. Introduction On 25th April 2015, a strong earthquake of moment magnitude Mw 7.8 hit central part of Nepal causing over 8000 casualties and nearly 23000 injuries. About 7 lakhs plus residential buildings, 4000 government offices and 8200 schools were damaged due to this earthquake. 14 districts were severely affected by this 2015 Gorkha Earthquake followed by several aftershocks[1].Various post damage assessment studies were made to assess the seismic performance of the existing buildings in Nepal so as to provide valuable insight to the seismic risk and future opportunities for retrofit and mitigation. Reinforced concrete (RC) buildings construction has increased drastically over the last few decades in the capital as well as other major urban centers of Nepal. According to the National census of 2011, about 10% of the buildings construction in Nepal is RC type, with more than 40% of the total RC construction are concentrated in the Kathmandu valley[2]. Recent field investigation shows that majority of the RC construction does not comply with the building code provisions.Majority of the buildings lacks gradual reduction of the stiffness as well strength reduction due to the absence of the infill at the ground story as well as load path discontinuity. These structural deficiencies increase the seismic vulnerability of the buildings[3]. In this context, present study focuses on the seismic fragility estimate of the existing RC vertically irregular buildings which helps to develop the vulnerability model for these type of the buildings. The demand estimate of the buildings has been done by the static pushover analysis of the buildings at the every floor level. Using the modal analysis results and pushover curves, fragility curves at the different limit states are evaluated using MATLAB code based tool SPO2FRAG[4]. To be structure-specific estimate of the fragility, the intensity measures are spectral acceleration Sa (T1) at the fundamental time-period of the buildings and the structural demand as Engineering demand parameter (EDP) which is inter-storey drift capacities at any story level. 2. Development of Analytical fragility estimate The next generation seismic design and assessment procedure for buildings within the performance based framework are radical departure from the traditional seismic design practice and performance assessment[5]. The performance bases seismic design and assessment approach, in which the building is expected to satisfy certain performance requirements in its lifetime, make a paradigm shift from traditional design and assessment procedure.The uncertainty and randomness in the building performance and seismic Pages: 589 – 594