Effect of Staircase on Earthquake Response of Medium Rise Moment Resisting Frame Building Using Response Spectrum Analysis

Abstract

Moment resisting frame (MRF) buildings have mainly two structural systems. These are primary structural system (beam and column) which resists all lateral load by frame action and secondary structural systems (staircase and walls) which are designed mainly for non-seismic forces. Even though structural modeling mostly does not include a staircase, it significantly contributes to the seismic response of the building by attracting rigidity center. The staircase acts as an inclined shear wall or as a different bracing system on either side based on its type. The objective of the study was to evaluate the effect of a staircase on earthquake response of medium-rise MRF building using Response Spectrum Analysis. Adama town wasselected as a study area since it is located in the great rift valley of Ethiopia which is characterized by a high seismic zone. The specific objectives were to evaluate the effect of staircase location, staircase type, and staircase orientation on the seismic response of regular and irregular plan buildings. The core methodology of the research was carried out by modeling and analysis of building with staircase and without staircase on ETABS V.18 to investigate seismic effect of selected staircase types. The four staircase types considered in this study are, straight flight with no landing, doglegged, L shaped, and U-shaped staircases. The study was done on 8-story MRF building with a regular and irregular plan. In this study staircases were provided at the center and corner of the building. Response spectrum analysis was used as seismic analysis method according to ES EN, 2015 code. According to analyses result based on lateral story displacement, story drift, base shear, base overturning moment, story stiffness, and eccentricity, staircases has significant effects on seismic response of buildings. The staircases provided at the center of regular and irregular building positively contributes to the story stiffness ranges from 3.48% to 28.86%. The effect is negative on stiffness of regular and irregular building having a staircase at the corner up to 7.96%. Doglegged staircase type less affects seismic responses of buildings as compared to other types of a staircase and best alternative to be provided at a corner of the building. The L-shaped staircase was the best alternative to be provided at the center of both regular and irregular buildings because it has a maximum and uniform seismic performance in both X and Y-directions. A straight staircase was orientation sensitive and it more resists seismic action in the longitudinal direction as diagonal bracing than in the in-plane direction.