Seismic Performance of Irregular building frames through Plan Irregularities

The rapid increase in aesthetic and limitation of availability of land led to trends of irregular building configurations. The irregularities in building led to reduction in seismic performance and making seismic design more challenging. Two such type of plan irregularities are the re-entrant corners and torsion in the irregular geometric buildings. These irregular buildings experiences high stress concentration at corners due to changes in torsion & stiffness in building which is vulnerable and shall need to analyze the seismic demand to lower the risk of damage. In this background, the present work is to analyze the effect of re-entrant corner building frames having different geometry shapes along with moment resisting systems when subjected to various incidence of angle of input time histories. To address this re-entrant corner irregular shape frames such as L-shape frames, T-Shape frames, H-Shape frames, and U-shape frames were modeled and analyzed along with one regular rectangular shape frame. The irregular geometric shape frames used in the present study comprises of three different re-entrant corner irregularity percentages i.e. 25%, 37.5%, and 56.25%. The Time history dynamic analysis is performed for the work. The input angle of incidence varies from 0° to 135°. The responses such as absolute displacement, maximum displacement, the impact of lateral torsional coupling, inter-story drift ratio, torsional irregularity ratio, base shear force, comprehensive damage index and diaphragm rotation demand is measured based on the angle of incidence. The result shows that high irregularity percentage in models are more vulnerable in seismic response. demands. It is evident that the L-shape frame is more sensitive to the various angle-incidence as compared to other shape models. The significant decrease in comprehensive damage index were seen in irregular shape models when subjected to 135-degree angle, versus a zero-degree angle of incidence. The codal approach yields a fundamental time period that is considerably lower than the one determined by the finite element method. This concludes that the provisions given in code is inadequate and further irregularities, and other major factors shall be present within the code approach and should be amended. The comprehensive damage index increases with increase in plan irregularity. Hence, the feasible solution is to reduce the irregularity effect in structure to improves performance and safety.