Analysis of C- Shaped Irregular Building using Staad Pro with Floating and Non-Floating Columns at Different Floor Levels

Abstract

Floating columns and swimming pool are widely used in modern urban multi-storey construction to meet architectural and parking needs. These are severely vulnerable to seismic loads due to broken load transfer paths. In the present study, an irregular C-shaped plan building with floating and non-floating columns at different floor levels with swimming pool provision using STAAD Pro is dealt with. The presence of a swimming pool adds an additional significant dead load and current demand of architectural designs for buildings for longer spans, which further complicate the seismic behaviour of an irregular structure. Equivalent static and response spectrum analyses are carried out to estimate the storey drift, lateral displacement, base shear and torsional effects for different seismic zones. Special attention is paid to the structural response of the swimming pool floor where the transfer of the hydrostatic pressure and the heavy water load through the supporting beams and floating columns require a higher flexural and shear capacity. Six structural models (M1–M6) representing different column arrangements and different seismic zone (III to V) were analysed under lateral loading in the X- and Z-directions. To evaluate the critically loaded paths and safety margins of structure under combined gravity and lateral loads, the load combinations as per Indian standard codes are considered. The aim of this study to analyse the multistorey building under the effect of lateral forces act on it by earthquake loads and then compare the results in the form of storey drift and storey displacement, Base shear graphs for the different structural models under different seismic conditions. The provision of swimming pool in the building also effects the building seismic response which also be analyse by this study. The obtained results are systematically compared for evaluating the variation in seismic response of buildings with floating and non-floating columns at different floor levels. Comparison of storey drift and displacement helps in identification of structural configuration with larger lateral deformation and thus larger seismic demand. Lastly the deign performed on model M5 and M6 to check which way is economical to make earthquake resistance building.

Introduction

The text presents a study on the seismic performance of C-shaped irregular multi-storey buildings with floating and non-floating columns, analyzed using STAAD.Pro. The main purpose is to understand how plan irregularity, vertical column discontinuity, seismic loading, and the placement of swimming pools affect structural behavior.

Background

C-shaped buildings are commonly used for architectural and functional reasons, but their re-entrant corners and uneven distribution of mass and stiffness can produce significant torsional effects. Under earthquake loading, these irregularities may increase storey displacement, storey drift, and uneven force distribution among beams and columns.

A floating column is a column that terminates at an intermediate floor rather than continuing to the foundation. Its load is transferred through a transfer beam or girder to supporting columns below. Although floating columns can provide open spaces for parking, lobbies, or other architectural requirements, they introduce a vertical discontinuity in the load path.

In contrast, non-floating columns continue continuously from the upper floors to the foundation, providing a more direct load-transfer mechanism.

Important Structural Parameters

The study evaluates structural behavior using several key parameters:

• Storey drift: Relative lateral movement between two consecutive floors.

• Storey displacement: Horizontal movement of an individual floor under lateral loads.

• Base shear: Total horizontal seismic force transferred from the structure to the foundation.

• Equivalent Static Method (ESM): Represents earthquake effects through equivalent horizontal static forces.

• Response Spectrum Method (RSM): A dynamic linear analysis method used to determine structural responses for different vibration periods.

Literature Review

Previous studies have examined floating columns, seismic response, shear walls, and irregular structures using STAAD.Pro. The reviewed research generally indicates that floating columns can increase lateral displacement and storey drift, particularly under stronger seismic conditions. Other studies suggest that shear walls can reduce these responses. Research on irregular buildings and swimming pools also demonstrates that changes in mass distribution and structural configuration can significantly affect seismic behavior.

Methodology

The proposed research follows a systematic modeling and analysis procedure:

1. AutoCAD modeling:
   The C-shaped building plan is first prepared in AutoCAD, including its dimensions, grids, beams, and column positions.

2. STAAD.Pro modeling:
   The AutoCAD geometry is converted into three-dimensional structural models in STAAD.Pro. Beams and columns are connected across successive floors to represent the building's three-dimensional behavior.

3. Floating-column configurations:
   Different models are created by changing the location and floor level of floating columns. Non-floating-column models are used as reference configurations.

4. Swimming-pool placement:
   Swimming pools are positioned at different locations, including the right wing, rear wing, and left wing of the C-shaped building. The pool introduces additional permanent and imposed loads, including water weight, structural weight, finishes, and potentially hydrostatic pressure.

5. Multiple structural models:
   Six different model parameters are considered to compare floating and non-floating column configurations under different seismic conditions.

6. Material and section properties:
   Appropriate material properties and beam/column dimensions are assigned. The same material and section properties are maintained across comparative models as far as possible so that the effect of floating-column placement can be examined more clearly.

Conclusion

1) All the analysed building models satisfy the permissible limits of storey displacement and inter-storey drift under the considered seismic loading conditions. It can be observed that the lateral deformation behaviour of the models is acceptable. 2) The higher the seismic zone class, the greater the storey displacement. The buildings exposed to higher seismic zone factors comparatively showing higher lateral displacement than the lower seismic zones. 3) The placement of floating columns has a great impact on the behaviour of the structure. Different patterns of displacement and drift are obtained for floating columns provided at different floor levels. This implies that the position of floating columns should be given due consideration in structural planning and design. 4) The results indicate that the lateral displacement generally increases with the increase in storey height, although fluctuations are observed at certain intermediate storeys due to variations in structural stiffness and configuration. Among the investigated models, M6 exhibits the maximum displacement, reaching approximately 15.2 mm at the 21st storey, followed closely by M5 with a displacement of approximately 15 mm. Model M4 also shows a comparatively higher displacement response, reaching approximately 12.5 mm around the upper storeys. In comparison, M1 and M3 exhibit moderate displacement responses of approximately 8.0 mm and 7.8 mm, respectively, at the uppermost storey. 5) The design runs for Models M5 and M6 were carried out to evaluate their structural performance and associated construction costs.

References

[1] Prof. Sarita Singla, Er. Ashfi Rahman (IJERT) (2015) “Effect of Floating Columns on Seismic Response of Multi-Storeyed RC Framed Buildings” Vol. 4 Issue 06. [2] Arpit Shrivastav, Aditi Patidar (SSRG - IJCE) (2018) “Seismic Analysis of Multistorey Buildings having Floating Columns” Volume 5 Issue 5. [3] Akash Agrawal, Anurag Wahane (IRJET) (2020) “Analysis of Elevated Swimming Pool with Different Positions on the Terrace of RCC Frames using STAAD Pro.” Volume: 07 Issue: 09. [4] Rashmi Agashe, Marshal Baghele, Vaishanvi Deshmukh, Sharad Khomane, (IRJET) (2020) “To Study Analysis and Design of Multi-Storey building using STAAD-pro. and Comparing with Manual Calculations” Volume: 07 Issue: 04. [5] Divya Nayak, Shubham Dashore. (JETIR) (2023) “Review on Structural Analysis of Building Structure with Floating Column” Volume 10, Issue 5. [6] IS: 875 (Part I) – 1987, “Code of Practice for Design Loads (Other than Earthquake) For Buildings and Structures”, Part 1 Dead Loads - Unit Weights of Building Materials and Stored Materials, Second Revision, September 2003. [7] IS: 875 (Part 2) – 1987, “Code of Practice for Design Loads (Other Than Earthquake) For Buildings and Structures”, Part 2 Imposed Loads, Second Revision and June 1998. [8] IS CODE 456-2000. RCC design [9] IS 1893 -2016 (PART -1) Criteria for Earthquake resistance design of structure [10] IS: 875(Part3): Wind Loads on Buildings and Structures -Proposed Draft & Commentary

Copyright

Copyright © 2026 Mr. Kamal Changotra, Prof. Sourabh Lalotra. 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.