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Comparative Study | Structural Engineering | Volume 15 Issue 9, September 2026 | Pages: 1192 - 1201 | India
Response Spectrum Analysis of an I-Shaped Building with Mass, Stiffness and Geometrical Vertical Irregularities
Abstract: Vertical irregularities in multi-storey reinforced concrete buildings can modify the spreading of mass, lateral stiffness and geometry along the height, thereby altering the dynamic characteristics and concentrating seismic demand. This paper presents a systematic comparative study of the influence of mass, stiffness, vertical geometric and combined irregularities on the seismic response of a G+15 RC special moment-resisting frame (SMRF) with an L-shaped plan. Thirteen 3D finite-element models were developed in ETABS and analysed using linear response spectrum analysis in accordance with IS 1893 (Part 1): 2016. One regular reference model and twelve irregular variants were considered, with irregularities introduced individually and in combination at one, two and three storey levels. The fundamental period, base shear, storey displacement, inter-storey drift ratio and storey acceleration were extracted in the two principal horizontal directions. The mass-irregular model with discontinuities at three levels recorded the maximum fundamental period of 2.134s, the maximum base shears of 25795.12kN (X) and 25103.29kN (Y), and the maximum X-direction roof displacement of 47.25mm. The vertical geometric-irregular model with discontinuities at two levels produced the maximum Y-direction displacement of 54.04mm and the largest floor accelerations of 949.9mm/s2 (X) and 960.5mm/s2 (Y). The combined-irregularity models governed the Y-direction drift ratio, reaching 0.00169. The findings show that no single irregularity type controls every response quantity, and that lower base shear does not necessarily indicate lower demand. Seismic evaluation of vertically irregular RC frames should therefore employ multiple response parameters simultaneously.
Keywords: Seismic response, Mass irregularity, Stiffness irregularity, Vertical geometric setback, Combined irregularity, Response spectrum analysis, ETABS
How to Cite?: D. S. S. Yaswanth, Dr. S Shameem Banu, "Response Spectrum Analysis of an I-Shaped Building with Mass, Stiffness and Geometrical Vertical Irregularities", Volume 15 Issue 9, September 2026, International Journal of Science and Research (IJSR), Pages: 1192-1201, https://www.ijsr.net/getabstract.php?paperid=SR26919100504, DOI: https://dx.doi.org/10.21275/SR26919100504