Structural Behaviour of Multi-Storey Buildings with Circular and Rectangular Columns under Earthquake Loads

Abstract

Moment-resisting frames (MRF) of reinforced concrete (RC) are the most popular structural system for multi-storey construction in seismically active zones and the size and shape of the columns have significant impact on the seismic performance of the MRF structure. The paper presents a comparative nonlinear static (pushover) analysis of a ten-storey (G+9) RC moment-resisting frame with six different types of cross-sectional area of the columns, three rectangular cross sections (450×600 mm, 500×600 mm and 550×600 mm), and three circular cross sections (250 mm, 300 mm and 350 mm). All the other geometric and material parameters were kept constant and shape and size of the columns were the only variables. The nonlinear static pushover analysis was performed based on the Indian seismic design provisions in ETABS, and seismic demand parameters were estimated by equivalent linearisation method developed by FEMA-440. The results of the Storey shear, Storey drift and Storey displacement indicate that the circular column configurations always have lower base shears than the rectangular column configurations of similar size, and storey drift and storey displacement are marginal, while equivalent-linearization performance points are more favourable. The six base-shear and storey-shear profiles in the above comparison confirm this tendency at all three size pairings, and show that circular columns have a slight seismic performance benefit over the rectangular columns in multi-storey RC frames.

Introduction

The text presents a study on the seismic performance of a ten-storey reinforced concrete (RC) moment-resisting frame, with particular emphasis on whether circular columns perform better than rectangular columns during earthquakes.

Earthquake ground shaking produces lateral forces that must be resisted by a building’s structural system. Since many existing buildings in seismic regions were designed before modern seismic codes or do not satisfy current requirements, evaluating their seismic performance is important. In an RC moment-resisting frame, columns resist both gravity and earthquake-induced forces. The shape and size of columns therefore have an important influence on structural behavior. Circular columns provide more uniform concrete confinement and have similar bending resistance in all directions, potentially giving them advantages over rectangular columns.

Objectives of the Study

The study aims to:

1. Evaluate the seismic behavior of a 10-storey RC frame with three different rectangular column sizes: 450 × 600 mm, 500 × 600 mm, and 550 × 600 mm.
2. Evaluate the same building using three circular column sizes with radii of 250 mm, 300 mm, and 350 mm, designed to have comparable cross-sectional areas and reinforcement ratios.
3. Compare the six models in terms of:
   • Storey shear
   • Storey drift
   • Storey displacement
   • FEMA-440 performance points
4. Determine which column shape provides the most favorable overall seismic performance.

All other building characteristics—such as storey height, bay arrangement, beam dimensions, slab thickness, materials, and seismic zone—were kept constant so that column cross-section was the primary independent variable.

Literature Review

Previous research has established that seismic performance depends on several factors, including school/building configuration, infill walls, ground-storey conditions, structural detailing, displacement capacity, and load patterns.

The literature indicates that:

• Pushover analysis is a widely used method for evaluating nonlinear seismic performance.
• Displacement-based assessment can be more appropriate than purely force-based approaches for evaluating seismic capacity.
• Infilled frames generally have lower collapse risk than bare frames.
• Open-ground-storey buildings can experience significantly greater ground-storey drift.
• Proper ductile detailing is highly important for structural capacity.
• Circular RC columns generally provide better confinement and can respond more effectively to strengthening or retrofit measures because of their continuous geometry.
• However, relatively few studies have examined whether the advantages of circular columns at the individual-member level translate into improved performance for an entire multi-storey building.

This study addresses that gap by comparing six otherwise identical ten-storey RC building models with different column shapes and sizes.

Methodology

A G+9 (ten-storey) RC building was modeled using ETABS. The building was designed for Seismic Zone V, with a zone factor of 0.36.

The six column configurations were:

• Rectangular: 450 × 600 mm
• Rectangular: 500 × 600 mm
• Rectangular: 550 × 600 mm
• Circular: 250 mm radius
• Circular: 300 mm radius
• Circular: 350 mm radius

The models used:

• M25 concrete for beams
• M30 concrete for columns
• Fe415 reinforcement
• 450 × 600 mm beams
• 125 mm slab thickness
• 3.0 m typical storey height
• 3.3 m ground-storey height
• Medium/Type II soil

The structural design followed relevant Indian standards, including IS 456:2000, IS 1893, IS 13920, and IS 875.

Pushover Analysis

The study used nonlinear static pushover analysis. First, gravity loads were applied using force control, followed by displacement-controlled lateral loading in the X-direction.

The analysis generated:

• Base shear versus roof displacement curves
• Storey shear
• Storey drift
• Storey displacement
• Structural capacity and performance levels

The performance levels considered were:

• Immediate Occupancy (IO)
• Life Safety (LS)
• Collapse Prevention (CP)

FEMA-440 Analysis

The study also applied the FEMA-440 equivalent linearization procedure to determine seismic performance points. This method represents the nonlinear structural system using an equivalent linear system based on effective period and equivalent damping, which depend on structural ductility.

The resulting performance points were used to compare the seismic demand and capacity of the six column configurations.

Overall Summary

The central idea of the study is that column geometry may significantly influence the seismic performance of an entire RC building. Circular columns have theoretical advantages because they provide more uniform confinement and similar bending properties in different directions. However, the study seeks to determine whether these member-level advantages actually produce better performance at the multi-storey building level.

By keeping all building parameters constant and changing only the column shape and size, the research provides a controlled comparison of three rectangular and three circular column configurations using ETABS, pushover analysis, and FEMA-440 performance assessment. The study therefore contributes to performance-based seismic design by examining whether circular or rectangular columns provide superior seismic behavior in a ten-storey RC frame.

Conclusion

For this purpose, 6 different configurations of a 10-storey RC moment-resisting frame (MRF) with comparable cross sectional areas of columns—(450 x 600 mm), (500 x 600 mm), (550 x 600 mm), (radius 250 mm), (radius 300 mm), and (radius 350 mm)—were selected and evaluated using a comparative nonlinear static (pushover) approach. The following conclusions are drawn based on the storey shear, storey drift, storey displacement and FEMA-440 equivalent-linearization results: 1) As the variation in cross-sectional shape of the column is the only variable used to differentiate between the two column families, the resulting effect is not primary, but measurable and is felt globally in the seismic response of the building being studied. 2) At all of the size pairs compared, 2. storey drift and 2. storey displacement are consistently (but not so significantly) greater for the rectangular column configurations than for the circular column configurations of comparable size. 3) In comparison, the FEMA-440 performance point achieved for these circular column configurations is associated with a reduced spectral displacement demand and a slightly reduced effective period in comparison with the corresponding rectangular column configurations, suggesting a slightly superior overall seismic performance for these circular column configurations. 4) In comparison to the gradual increase in seismic base shear with increasing cross-sectional area of the circular column sets, the larger rectangular column sets (500×600 mm and 550×600 mm) share a disproportionately larger portion of the seismic base shear. 5) These findings are aligned with member-level studies that show good confinement and retrofit performance for circular RC columns, [4, 5, 19, 23], and are expanded from the level of a single member to the level of a full-scale multi-storey building analysed using pushover analysis. 6) It would be useful for future work to incorporate explicit shear and joint failure criteria, to confirm the conclusions drawn from the pushover analysis using nonlinear time-history analysis, and to broaden the range of column configurations for machine-learning-based surrogate modelling (as presented by Montes Rodriguez et al. [24]).

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Copyright

Copyright © 2026 Shahnavaj ., 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.