Comparative Study on the Behavior of Irregular Multi-storey Reinforced Con crete Building using Equivalent Static Method and Dynamic Response Spectrum Method

Abstract

Irregularity of multistory buildings introduced in many modern structures due to their aesthetic value, utili ties and functionalities. The irregularity of multistory buildings should take account to be recognized, they may result in unexpected damage and collapse. The present study conducts building models with different type and location of irregularity. The behaviour of structure using equivalent static and dynamic response spectrum analysis of seismic responses of building models have been compared with that of the regular building model. The different forms of behaviour of structure mass, stiffness, and setback structural irregu larities have been introduced in the regular building model to generate irregular building models. In the present study, three single and two multi-combination irregularity of multistory reinforced concrete building subjected to high seismic zone V are investigated using equivalent static and dynamic response spectrum analysis method by using ETABS (Extended Three-dimensional Analysis of Building System) soft ware with respect to the regular structural model of storey 8 and 15 frame building. Load consideration was done based on Ethiopian Building Code ES EN 1998-1:2015. Structural response of base shear, story shear, storey drift and storey displacements were analyzed. The result of base shear and shear force obtained using response spectrum analysis is greater than equiv alent static analysis for analyzed regular and irregular structural model and for both story 8 and 15 rise building. Irregularity of base shear and shear force less with respect to regular building. Mass irregularity cases have shown greater base shear and storey shear for analyzed regularity and irregularity, due to the increase in the mass of the structure building at different story floor levels Maximum result of story drift and story displacement is obtained by equivalent static analysis than response spectrum analysis from analyzed irregularity. Story drift and story displacement of irregular building is very maximum with compared to regular structure. Both Story drift and story displacement of irregular building increase as story height building increase. Combination irregularity have maximum story drift and story displacement than singular irregularity, especially the value of comb 2 irregularity extremely high. The sequence increases of story drift and story displacement of analyzed irregularity are R<SBI<MI<SI<Comb1<Comb2 building. For all studied cases, the sudden increase in the storey drift and storey displacements value is observed at the areas of discontinuity presents in the geometric configurations of the structural model of irregularity. The difference of values of story drift and story displacement between static and response spectrum analysis in higher story and equivalent static analysis gives higher values than dynamic response spectrum analysis. Comparative study on the behavior of Irregular Multi-story Reinforced concrete building using equivalent static method and dynamic response spectrum method JIT, Jimma Institute of Technology Page II Building with stiffness and combination irregularity has more lateral story drift and reduction in base shear and story shear capacity compared to regular buildings. When compared to irregular configuration the story drift value is more in the regular structural model configuration. Story drift is increased as the height of the building increases from story 8 to story 15 rise building. Generally, the Stiffness, mass, setback and their combination irregularity causes twisting of buildings under lateral load due to the center of mass and center of stiffness of different storeys do not lie along the same vertical line, as is the case in buildings with regular overall geometry. By using response spectrum analysis methods we get more accurate responses than equivalent static analysis for irregular multi-storey for high rise building. So that in the modern high rise multi-storey building response spectrum analysis methods are the most better and save than equivalent static analysis according to our code of standard ES EN 1998-1:2015.