Effect of Soft Storey on Multi-storey Building

Abstract

In the present work study is carried out for the behavior of G + 10 storied RC buildings with Rectangular shaped plan of soft storey at different levels. Floor height provided as 3.4m and also properties are defined for the irregular R.C building modelled in STAAD. Pro V8i software. Here twelve models are created in which soft storey is provided at ground, fifth and eleventh storey in all four seismic zones. From result it is found that Location of Soft storey effects seismic behavior of building in every zone from low to high seismicity. As the location of soft storey goes upper it gives more stable structure compared to soft storey at ground level. Soft storey at top level of structure is more stable than soft storey at middle part of structure, soft storey at top level gives Lower values of displacement in all seismic zones.

Introduction

Summary:

The study addresses the seismic vulnerability of buildings with soft storeys—typically those having parking or commercial spaces on lower floors with fewer infill walls—leading to reduced lateral stiffness and potential collapse during earthquakes. Soft storeys cause irregularities in vertical stiffness, concentrating seismic forces and increasing the risk of failure.

Literature Review:
Various researchers have analyzed seismic behavior of soft storey buildings using different structural models (bare frames, infill frames, braced frames, shear walls) and analysis methods (static, dynamic, linear, nonlinear). Key findings include:

• Infill walls improve stiffness and seismic resistance but may not fully prevent soft storey failure.

• The common multiplication factor (2.5) for open ground storey design may be excessive or unrealistic for low-rise buildings.

• Mass and geometric irregularities increase structural demands.

• Nonlinear analyses reveal brittle failure modes in soft storey buildings.

• Ignoring infill walls in analysis leads to underestimating base shear and seismic forces, risking collapse.

Methodology:
A G+10 irregular RC building with soft storeys at different levels (ground, fifth, eleventh floors) was modeled and analyzed under various seismic zones using STAAD Pro software and Indian seismic codes. Equivalent static analysis evaluated axial forces, moments, displacements, base shear, and story drift.

Results:

• Soft storey location affects maximum axial forces, moments, displacements, base shear distribution, and reinforcement requirements.

• Models with soft storeys at the ground floor generally showed higher axial forces and displacements.

• Seismic zone influences seismic demands, with higher zones producing larger forces and displacements.

• Reinforcement needs varied with soft storey location, indicating the importance of targeted design.

Conclusion

1) Location of Soft storey effects seismic behavior of building in every zone from low to high seismicity. 2) As the location of soft storey goes upper it gives more stable stable structure compared to soft storey at ground level. 3) Soft storey at top level of structure is more stable than soft storey at middle part of structure.

References

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Copyright

Copyright © 2025 Sanket P Sharma, Prof. R. M. Phuke. 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.