Impact of Earthquake Incident Angles on Displacement in Un-Symmetrical Buildings

Abstract

Introduction

Overview

India is highly vulnerable to natural disasters, especially earthquakes, with 85% of the area at risk and 57% in high seismic zones, including Delhi. Earthquake simulation is complex, and building failures often stem from irregularities in shape, mass, stiffness, or strength. Unsymmetrical structures are particularly vulnerable. This study examines how incident angles of seismic forces (0°, 30°, and 60°) impact the seismic behavior of different RC (Reinforced Concrete) building shapes.

2. Objectives

The main goals of the study are:

1. Analyze seismic performance of RC buildings with different plan geometries (L, Plus, Square).

2. Evaluate displacement responses using time history analysis.

3. Study the effect of varying earthquake incident angles on building performance.

3. Methodology

• Software: ETABS 2018

• Structures: Three G+5 RC buildings (L, Plus, and Square plan shapes)

• Time history: El Centro Earthquake (1940, magnitude 7.1)

• Parameters: Incident angles considered were 0°, 30°, and 60°

• All buildings followed uniform material specs: M20 concrete, Fe415 steel, and same dimensions.

4. Analysis

• Each building shape was subjected to seismic forces at the three incident angles.

• Time history analysis was performed using ETABS to evaluate roof displacement as a key indicator of structural response.

5. Results

• Maximum displacement occurred at 30° incident angle for all building shapes.

• Displacement increased by 2%-3% from 0° to 30° and then decreased by 7%-8% from 30° to 60°.

• L-shaped buildings showed the highest roof displacement, 14.34% more than other shapes.

• Square and Plus shapes showed similar displacement patterns, with smoother performance.

Conclusion

Following conclusion are found. 1) The analysis indicates that displacement reaches its peak at an incident angle of 30° for all building shapes. However, to accurately identify the most critical incident angle, it is recommended to conduct further investigations with smaller increments between 30° and 60°. 2) The findings reveal that L-shaped buildings exhibit higher displacement under seismic forces compared to other configurations, such as plus-shaped and square-shaped buildings. This suggests that asymmetrical structures are less favorable due to their reduced strength and stability against earthquake-induced forces. 3) Square-shaped buildings demonstrate superior resistance to seismic forces and exhibit enhanced structural stability. Therefore, symmetrical building configurations are recommended to ensure optimal seismic performance.

References

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Copyright

Copyright © 2025 Kajal Late, Prof. A. A. Kusnale. 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.