Seismic Analysis of Multi-Storey Reinforced Concrete Buildings with Floating Columns: Structural Performance, Design, and Cost Assessment

Abstract

In this paper, research on the structural behaviour of a G+2 reinforced concrete (RC) building both with and without floating columns (FC) subjected to seismic Zone II conditions in Mandideep, Bhopal (M.P.), India were carried out. The STAAD Pro V8i was used to achieve both the static (equivalent static method) and dynamic (response spectrum) analysis in accordance with the requirements of IS 1893 (Part 1): 2002, and the structural members were designed in accordance with the requirements of IS 456:2000. The major parameters considered are the displacement, bending moment, shear force, axial force, storey drift, peak storey shear, mode shapes and material cost. The findings indicate that floating columns present substantial structural anomalies: there is column movement by 61.8 percent, beam bending by 532 percent and base shear by 26.9 percent and the total cost of construction is 16.02 higher. The results are validated by benchmarking the findings with the results published in the recent past. The research provides a novel input to the existing literature through discussing an unsymmetrical plan with long-span transfer beam in the lowest Indian seismic zone - a set up which has not been represented in any literature.

Introduction

The text analyzes the seismic performance of G+2 reinforced concrete (RC) buildings with and without floating columns (FCs) under low-seismic Zone II conditions. Floating columns, supported by transfer beams rather than extending to the foundation, create a “soft storey” effect that increases vulnerability to seismic forces by disrupting the direct load path. Past studies show that FCs lead to higher inter-storey drifts, reduced natural frequency, increased bending moments, and elevated expected losses even in low-seismic zones.

Key findings from the study:

• Structural modeling: G+2 RC buildings in Mandideep, Bhopal, were modeled in STAAD Pro with detailed geometry, material properties, and loading parameters according to IS 1893:2002 and IS 456:2000. FC buildings had larger transfer beams and reinforced columns to support point loads, while WFC buildings had uniform beams and columns.
• Static analysis: FC buildings showed 61.8% higher column displacement and a 532% increase in beam bending moments compared to WFC buildings, necessitating larger cross-sections and heavier reinforcement.
• Dynamic analysis: Response spectrum analysis revealed that FC buildings are more flexible with lower natural frequencies, leading to higher seismic response under excitation. Mode shape analysis confirmed larger deformations in FC structures.
• Implication: Even in low-seismic zones, floating columns significantly degrade seismic performance, requiring careful design of transfer beams and reinforcement to mitigate risks.

In short, the study highlights that floating columns, while enabling architectural flexibility, dramatically increase seismic vulnerability and require substantial structural reinforcement, both in static and dynamic contexts.

Conclusion

1) The design and analysis of a G + 2 RC building with floating columns and without floating columns using a complete seismic and a dynamic analysis including both the statical and dynamic analysis was carried out. One can conclude the following: 2) There is no problem with either building when loaded statically, although the internal forces and displacements are very large in the FC building. 3) Known problems FC structures cannot withstand dynamic seismic loading without extension of members. Only structural safety is ensured after deepening transfer beam to 500 mm and increasing column sections. 4) • FC building consume 27.4 percent more concrete, 15.1 percent more steel and 16.02 percent more construction cost compared to the WFC building. 5) Column shift is higher by 61.8, beam bending moment by 532 and base shear by 26.9 percent in the FC arrangement. 6) Storey drift increases in the Z-direction by 193% with Mode Shape 1 having control over the dynamic response. 7) Although floating columns have structural issues, they are vital in architecture in terms of their layout remedial effects - removal of layout anomalies and the creation of large open spaces - and are structurally feasible with a good design, with detailed transfer beam detailing and reinforcement. 8) As a precautionary measure, seismic analysis and detailing of floating column buildings is required even in Zone II (lowest seismic zone)

References

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Copyright

Copyright © 2026 Ravikant Prajapati, Mrs. Ankita Singhai, Dr. Rahul Kumar Satbhaiya. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.