PSI - Issue 14

Siva Naveen E et al. / Procedia Structural Integrity 14 (2019) 806–819 Siva Naveen E, Nimmy Mariam Abraham, Anitha Kumari S D / Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction The behavior of any building depends on the arrangement of structural elements present in it. The important aspects on which the structural configuration depends are geometry, shape and size of the building. When a building is subjected to dynamic loads, inertia forces are developed and gets concentrated at the center of mass of the structure. Usually, the vertical members such as columns and shear walls resist the horizontal inertia forces and the resultant of these forces gets concentrated at a point called center of stiffness. When the center of mass doesn’t coincide with the center of stiffness, eccentricity develops in the structure. Eccentricity occurs due to the irregular arrangement of structural configuration which in turn induces torsion in the structure. Location and size of structural elements have significant effect on torsional coupling which results in damage of structures. Regular structures have no significant discontinuities in plan or in vertical configurations. Irregular structures have certain physical discontinuities either in plan or in elevation or both which affect the performance of the structure subjected to lateral loads. Irregularities in the distribution of mass, stiffness and geometry along the height of any building are grouped as vertical irregularities. Horizontal irregularities can be attributed to the presence of discontinuities in plan. Different structural irregularities affect the seismic response of structures in different ways. Irregularities are introduced in real structures for both aesthetics and utility. The magnitude of variation in response depends on the type, degree and location of irregularities present. The judicious choice of these parameters in the design of structures improves performance of the structure. So far, many researchers have investigated the effect of seismic response on structures having vertical and horizontal irregularities. Valmundsson and Nauhave (1997) studied the seismic behavior of multistoried buildings having vertical structural irregularities and concluded that 30% decrease in stiffness have increased the storey drift in the range of 20-40%. Guevara et al. (1992) focused on the effect of floor plan on the seismic behavior of structures. Study includes the dynamic analysis of H and L shaped buildings. The paper suggests that buildings having H and L shaped plan should be divided into rectangular blocks separated by seismic joints. Wood (1992) investigated the effect of seismic response of setback structures and concluded that the presence of setbacks did not affect the seismic behavior. The behavior was found to be similar to that of regular structure having no setback. Khoure et al. (2005) studied the response of nine-storey steel frames with setback irregularities and observed that the higher torsion response at the upper portion of the setbacks. Tremblay and Poncethave (2005) studied the dynamic behavior of building frames with irregular distribution of mass. They have concluded that both static and dynamic analysis methods are ineffective in predicting the response of the frames having mass irregularity. Gokdemi et al. (2013) studied the effect of torsional irregularity on structures. According to the authors, torsion is caused due to the eccentricity between center of mass and center of stiffness. The intensity of moment due to torsion was found to be a function of eccentricity ratio. Ozmen et al. (2014) performed parametric studies on six buildings with varying shear wall positions. Based on the floor rotations, a torsional irregularity coefficient was proposed. According to their findings, as the number of storey decreases, the torsional irregularity coefficient increases and the maximum storey rotations occur for the top storeys. Ahmed et al. (2016) have studied the effect of seismic response of L shaped buildings. Equivalent static and response spectrum methods were performed using ETABS software. They observed that the response of L shaped building is higher than that of the regular frame due to torsion. Patil et al. (2017) studied the dynamic response of multi-storey buildings with plan asymmetry. They have numerically analyzed multi storyed frames having different plan shapes. They have reported that the increase in height of T and L shaped buildings increases the displacement response and stress at the re-entrant corners. As per the study conducted on existing literature, researchers have mainly focused on single irregularity. The works reported are mainly related to mass, stiffness or geometry. Real structures contain multiple irregularities in various combinations. However, the studies on the effect of combination of irregularities are scarce. Hence, the present research addresses the behavior of structures having combination of irregularities, subjected to ground motion. The study includes the analysis of both regular and irregular multistoried reinforced concrete (RC) frames. Irregularities in both elevation and plan are studied. The vertical irregularities considered for the study include mass, stiffness and vertical geometric irregularities. The horizontal irregularities considered are torsion and re-entrant corner irregularities. A total of 54 irregular frames are analyzed. Out of the cases studied, 34 configurations have single irregularity and 20 possess combination of irregularities. The main purpose of the study is to identify critical combinations of irregularities.