Analysis of Steel Structure with and Without Infill

Abstract

The present study focuses on the seismic performance evaluation of a steel structure considering two configurations: a bare frame and the same frame with infill. The analysis aims to understand the influence of bare frame & infills on the seismic behavior of steel buildings, particularly in high seismic risk areas. A G+9 storey steel framed building is modeled and analyzed using ETABS software. The structure is located in Seismic Zone IV as per IS 1893:2016, with an importance factor of 1.5, reflecting its critical nature. The seismic analysis is carried out using the Response Spectrum Method, which effectively captures the dynamic characteristics of the structure under earthquake loading. Three models are developed: one representing the bare steel frame, and the other incorporating infills with Masonry & Glass. The primary parameters compared include base shear &storey displacement. The results indicate that the inclusion of glass infill panels alters the dynamic response of the building significantly. While the stiffness and lateral load resistance increase due to infills, the overall displacement values show noticeable variation when compared to the bare frame. This study emphasizes the importance of considering non-structural components like infills in seismic design and highlights their potential contribution to overall structural performance during earthquakes.

Introduction

Earthquakes are unpredictable natural disasters that generate lateral forces on structures, potentially causing severe damage or collapse, especially in high-rise buildings located in seismic zones. The rapid urbanization and construction of tall buildings pose challenges for engineers, as these structures are highly vulnerable to seismic and wind-induced forces. The structural performance during earthquakes depends on factors such as earthquake intensity, building design, material properties, and structural configuration.

Infill in Buildings:
Infill refers to non-structural panels or walls placed between columns and beams. Common infill materials include masonry, glass panels, AAC blocks, and gypsum boards. While infills are not primary load-bearing elements, they significantly affect seismic performance:

• Masonry infill: Increases lateral stiffness, reduces inter-storey drift, but may cause brittle failure if not integrated properly.

• Glass infill: Offers aesthetic value and natural lighting but minimal lateral resistance, posing safety risks in earthquakes.

• Proper detailing of infills is critical to balance structural safety, stiffness, and energy efficiency.

Literature Review:
Recent studies highlight strategies to improve seismic resilience of high-rise buildings:

• Steel bracing (e.g., Inverted-V type) improves stiffness, lateral resistance, and reduces torsional effects.

• Seismic Response Spectrum Analysis enables performance-driven material optimization for steel structures.

• Bracing systems, including modern innovations like diagrids, are essential for safety, cost efficiency, and sustainable high-rise design.

Research Objectives:

1. Analyze seismic behavior of multi-storey steel structures under dynamic loads.

2. Compare the performance of different infill materials (masonry vs. glass).

3. Evaluate structural parameters like base shear and displacement.

Structural Modeling and Analysis:
Three 10-storey steel building models were analyzed using ETABS:

1. Bare Frame Model (BFM) – without infill.

2. Three-side masonry + one-side glass panel (TSP&OSW).

3. Four-side glass panel (FSP).
   Design followed Indian standards, considering dead, live, and earthquake loads. Both linear static and response spectrum analyses were performed to assess structural behavior and the impact of infill materials on lateral resistance and displacement.

Key Insights:

• Masonry infills increase base shear resistance and lateral stiffness compared to bare frames.

• Glass infills contribute less to structural strength and may lead to higher displacements under seismic loads.

• Proper selection and integration of infill materials are critical for earthquake-resistant high-rise design.

Conclusion

The study reveals that the presence of infill walls significantly increases the storey shear capacity of the structure when compared to the bare frame model. 1) The three-side masonry wall & one-side glass panel configuration demonstrated the highest storey shear values in both EQ and RSA methods, indicating greater lateral stiffness and load resistance. 2) The four-side glass panel model also improved shear resistance over the bare frame, but performed lower than the masonry wall model due to the lower stiffness of glass infills compared to masonry. 3) RSA consistently produced higher storey shear values than EQ for all models, emphasizing its capability to capture dynamic effects more accurately. 4) Overall, masonry infill significantly enhance seismic performance, while glass infill provide moderate improvement over a bare frame. The selection of infill type should balance structural stiffness, architectural needs, and seismic safety requirements. 5) Infill significantly reduce storey displacement compared to bare frame structures, enhancing lateral stiffness. 6) Masonry infill walls provide better displacement control than glass panels due to higher rigidity and mass contribution. 7) RSA consistently produces higher displacement values than EQ, indicating its greater sensitivity to dynamic effects. 8) For earthquake-resistant design, incorporating masonry infill is more effective in controlling lateral deflections, whereas bare frames are the most flexible but most vulnerable to seismic displacements.

References

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Copyright

Copyright © 2025 Sangeetha T. R., Pradeep A. R., Anusha P, H Siddesha. 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.