P DELTA (P-∆) EFFECT ON MULTISTORIED REINFORCED CONCRETE FRAMED BUILDING WITH VERTICAL ERRIGULARITIES M. Mahsin 1* , S. M. Mozundar 1 & M. S. Uddin 2 1 Civil Engineering, Southern University Bangladesh, Chittagong, <mh_mahsin@yahoo.com> 2 Civil Engineering, Southern University Bangladesh, Chittagong, < saif08cuet@gmail.com> *Corresponding Author ABSTRACT The demand of high rise building is increasing day by day to accommodate more people in less space. Generally, P-Delta analysis is not performed during design and analysis of Reinforced Concrete framed structure. High rise structure may collapse under severe perimeters if ‘P-Delta’ analysis is not considered in the analysis and design phase. Due to defective construction practices and ignorance for earthquake resistant design of buildings in our country, most of the existing buildings are vulnerable to future earthquakes. This study deals with the analysis of RC framed regular and irregular buildings in Zone-IIΙ using inelastic method (P-Delta Analysis). The objective of this study is to find out the effect on response quantities (Story Drift, Displacement & Stiffness) due to ‘P-Delta’ effect on the RC framed structure and also find out the effect of asymmetry on this analysis. ‘P-Delta’ analysis is nonlinear static analysis, so the structural responses are included the additional response produced due to the simultaneously action of lateral and gravity load on un-deformed as well as deformed geometry. After analysis, it is found that the response quantities are higher if ‘P-Delta’ effect is considered and in the case of irregular structure the response quantities are higher in compare to the regular structure. Keywords: P-Delta, Earthquake, Vulnerable, Design, Geometry, RC building, INTRODUCTION ‘P-Delta’ is a non-linear effect that occurs in every structure where elements are subject to axial load. ‘P-Delta’ is actually second-order effects. It is a genuine effect that is associated with the magnitude of the applied axial load (P) and a displacement (delta). [1] ‘In structures responding elastically, the P–Δ (P=Axial load, Δ=Displacement due to horizontal load) effect produces a reduction of the initial elastic stiffness, and corresponding elongation of the periods of vibration. In those responding in-elastically, there are also reductions in their strength. These reductions in strength and stiffness are measured with respect to their values when the P–Δ effects are ignored.’ [2] The effect of P-Delta is mainly dependent on the applied load and building characteristics. In addition to this, it also depends on the height, stiffness and asymmetry of the building. The building asymmetry may be unbalanced mass, stiffness, on the plane. The deformation caused by torsion can affect the P-Delta. The type of lateral load resisting system plays an important role in the degree that torsion modifies the P-Delta effect so it is concluded that the lateral load resisting system has importance in the case of torsion deformation. The reason is that implementing P-Delta effects in analysis causes a change in stiffness matrix of the building, thus the natural periods and other dynamic properties of the building will change. If acceleration response corresponding to the new natural period of building, in 1st International Conference on Research and Innovation in Civil Engineering (ICRICE 2018), 12 –13 January, 2018, Southern University Bangladesh (SUB), Chittagong, Bangladesh ISBN: 978-984-34-3576-7 170