IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 13, Issue 4 Ver. VI (Jul. - Aug. 2016), PP 46-52 www.iosrjournals.org DOI: 10.9790/1684-1304064652 www.iosrjournals.org 46 | Page Evaluation of Angle of Excitation for Torsion by Using Irregularities in R.C.C Frame Danish Ali 1 , Mangulkar Madhuri N 2 1 (P.G. Student, Department of civil Engineering, J.N.E.C, Aurangabad, Maharashtra, Indi) 2 (Assistant Professor, Department of civil Engineering, J.N.E.C, Aurangabad, Maharashtra, India) Abstract: Torsional behaviors of asymmetric and irregular R.C.C structures are one of the most frequent sources of structural failure during strong ground motions. In this paper G+ 9 stories irregular shape building considered with mass, stiffness irregularity. For the evaluation of critical angle of seismic incidence for torsion by using dynamic analysis response spectrum method in STAAD PRO as per I.S 1893-2002. Set values from 0 to 90 degree with increment of 10 degree interval have been used for angle of excitation. Building column divided into three main categories including corner, side and middle column. The angle at which maximum torsional moment is obtain that is considered as a critical angle and results are compared in terms of axial force, bending moment and shear force for column. Keywords:Mass and Stiffness Irregularity, I.S 1893-2002, Torsion, Angle of Excitation, Column Forces. I. INTRODUCTION Because of the nature of earthquake, a dual design philosophy has been adopted for the design of building in earthquake prone regions. The buildings which do not fulfill the requirements of seismic design, may suffer extensive damage or collapse if shaken by a severe ground motion. The seismic evaluation reflects the seismic capacity of earthquake vulnerable buildings for the future use. It has been analyses that survey conducted on modes of failure of building structures during past severe earthquakes concluded that most vulnerable building structures are those, which are asymmetric in nature. Asymmetric-plan buildings, namely buildings with in-plan asymmetric mass and strength distributions, are systems characterized by a coupled torsional-translational seismic response. Asymmetric building structures are almost unavoidable in modern construction due to various types of functional and architectural requirements. IS 1893-2002 code deal with torsion by placing restrictions on the design of buildings with irregular layouts and also through the introduction of an accidental eccentricity that must be considered in design. The lateral-torsional coupling due to eccentricity between center of mass (CM) and center of rigidity (CR) in asymmetric building structures generates torsional vibration even under purely translational ground shaking. During seismic shaking of the structural systems, inertia force acts through the center of mass while the resistive force acts through the center of rigidity as shown in figure No.1. Figure No.1:- Generation of torsional moment in asymmetric structures during seismic excitation. Although irregular buildings are preferred due to their functional and aesthetic considerations torsion is generally occur due to irregularities in frame structure following are the different types of irregularities as shown in figure No.2 The framed structure is one of the most significant modern developments in high rise structural form. The lateral resistance of framed structures of different geometric plans (H-shape, T-shape, Irregular shape etc.) is provided by very stiff moment resisting frames. The gravity loading is shared between interior columns. This structural form offers an efficient, easily constructed structure appropriate for buildings less than 40 meters. Design eccentricities include a multiplier on the static eccentricity to account for possible dynamic amplification of the torsion. Also, the design eccentricities often include an allowance for accidental torsion that is supposed to be induced by the rotational component of ground motion, by possible deviation of the ECR(elastic center of resistance) and center of mass (CM) from their calculated positions or by unfavorable distribution of live loads. The design eccentricity formulae given in B.I.S 1893-2002 code can be written in the following form.