Study of Seismic Analysis for Vertical Extension of Multi Storey Building - A Review

Abstract

Expanding horizontally is impractical sometime because in this era where urban areas are rapidly developed, peoples have shortage of land due to financial aspect and limited space. In this situation vertical extension of building is more ideal solution then Horizontal expanding or construct the new building from the scratch. But due to lack or awareness and economical point of view house owner or developers may prioritize minimizing cost. As a result of sometime peoples are not designed our building for future extension, for that and due to revised seismic standard building need to redesign and check for seismic loading. In this study we are evaluate the importance of study in vertical extension with comparing the various research available for seismic analysis of multi storey building like Dynamic analysis (Time history method or Response spectrum method) with or without geometrical non linearity. This study suggests that for building more than seismic zone 2, dynamic analysis is required to get the proper response during seismic event, before extending any storey above it. Also suggested If requires do retrofitting of the building according to dynamic analysis of building before extension

Introduction

Context & Importance:
Vertical extension—adding floors to existing multistorey buildings—is a common but critical practice, especially in earthquake-prone regions. Despite many studies on seismic analysis of buildings with varying heights and shapes, limited research focuses specifically on vertical extensions. Many homeowners extend buildings without professional advice, risking structural failure during earthquakes.

Objective:
The study aims to review existing research on seismic behavior of buildings and emphasize the need for focused research on vertical extensions using dynamic analysis methods.

Methodology

The review categorizes research into four areas:

1. Importance of dynamic analysis for buildings.

2. Comparison of Response Spectrum Analysis (RSA) and Time History (TH) Analysis.

3. Role of P-delta effects (non-linear secondary effects) in seismic behavior.

4. Rationale behind the need for studying vertical extensions.

Key Findings from Literature Review

• Seismic Behavior:

  • Base shear and storey shear increase by approximately 50% with each higher seismic zone (e.g., zone II to V), causing higher internal stresses and displacement in buildings.

  • Regular buildings show higher base shear due to greater stiffness; however, irregular buildings experience larger displacement under seismic loading.

  • Rectangular-shaped buildings perform better than square or irregular shapes in seismic response due to better stiffness.

  • Adding structural elements like cross struts can reduce displacement by up to 67%, improving building flexibility and seismic resistance.

• Dynamic Analysis Techniques:

  • Time History Analysis provides more accurate but time-consuming results compared to Response Spectrum Analysis, which is faster but less precise.

  • Dynamic analysis is crucial for irregular and high-rise buildings, as static methods often underestimate seismic effects.

  • P-delta effects increase displacements and moments; hence, including these non-linear effects leads to more realistic structural behavior predictions.

• Vertical Extension Studies:

  • Vertical extensions increase loads on structural elements, requiring additional reinforcement and strengthening, especially in columns and foundations.

  • Older buildings designed with elastic analysis have reserve strength but may require member enlargement or reinforcement under modern limit-state codes.

  • Vertical extension is a sustainable urban strategy, promoting housing densification without urban sprawl, reducing construction waste and carbon emissions.

  • Energy-efficient renovations combined with vertical extension improve building sustainability, reduce energy use, and enhance financial viability.

  • Lightweight and industrialized construction methods for vertical extension are innovative approaches to minimize additional loads and ease construction.

• Practical Considerations:

  • Structural assessment must include load-bearing capacity of existing foundations and soil conditions.

  • Strengthening strategies vary: some columns need reinforcement increases of 12-17%, while lateral wind loads are less impactful after vertical extension.

  • Vertical extensions can improve housing availability and community quality of life but require careful design adjustments and ongoing evaluation.

Conclusion

Based on the findings of several studies, the following conclusions have been reached: 1) An existing building strength and soil capacity is crucial factor to considered in analysis before proceeding with vertical extensions. 2) Earthquake load effects increase significantly with extension because seismic weight of the building also increases. 3) Generally, for mid rise building, Wind load does not show significant effect after extension of building. 4) Vertical extensions increase loads on existing structural elements. Due to which load bearing elements experience higher utilization ratio, as a result of more reinforcement. 5) Even modern codes may reveal strengthening of building due upgradation of zone with extension. But reinforcement adequacy must still be verified. 6) The composite action of new concrete with existing concrete must be considered. 7) Lightweight and industrialized construction methods are recommended for vertical extensions on older buildings. 8) The removal of unnecessary weight from lower floors can help offset the added load of the extension. 9) Rectangular building exhibit better seismic performance, so for future extension plans use rectangular building shape then other. 10) Dynamic analysis methods (Response Spectrum and Time History) provide more accurate results than static linear analysis (Equivalent Static Method), especially for high-rise and irregular buildings. 11) Time History analysis is considered the most accurate but is computationally intensive and less economical than Response Spectrum analysis. 12) Response Spectrum analysis is a good and fast option for low to mid rise building. Also used for determine the behavior of building during earthquake before and after extension. 13) Considering P-Delta effects in analysis significantly increases displacement and bending moments, indicating its importance for accurate structural behavior prediction. 14) Vertical extensions are a viable solution for increasing housing capacity, especially in urban areas with limited land. Densifying cities, reducing urban sprawl, and minimizing construction waste. 15) Vertical extensions can be used to improve the energy efficiency of existing buildings.

References

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Copyright

Copyright © 2025 Neeraj Singh Saral, Rakesh Kumar Grover. 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.