Review Paper on Research Done in Effects of Outrigger Systems in High Rise Buildings in Siesmic Zones

Abstract

Introduction

An outrigger system is a structural solution widely used in high-rise buildings to resist lateral loads (e.g., wind and earthquakes). It connects the central core of the building to outer edge columns using horizontal rigid arms, usually deep beams or trusses, often combined with a belt truss. This system helps reduce bending and swaying, increases stiffness, and improves structural stability by distributing lateral loads more efficiently.

Purpose and Behavior

• The core wall alone becomes less effective at resisting lateral forces as building height increases.

• Outriggers brace the core and transfer part of the overturning moment to the outer columns through tension and compression.

• This system decreases lateral displacements and increases structural rigidity and resistance to overturning.

Types of Outrigger Systems

1. Conventional Outrigger System: Directly connects the core to edge columns through outriggers and belt trusses.

2. Virtual Outrigger System: Uses floor diaphragms to transfer forces indirectly, improving flexibility and avoiding construction complications.

Static and Dynamic Analysis

Structural systems like:

• Outrigger Braced Frame (OBF)

• Moment Resisting Frame (MRF)

• Pendulum Tuned Mass Damper (PTMD)

are evaluated under static (gravity/wind) and dynamic (earthquake) loads. Outrigger systems (especially OBF) show superior performance in seismic resistance, controlling displacement, velocity, and acceleration better than some damping systems.

Advantages of Outriggers

• Increase lateral stiffness and reduce core overturning.

• Minimize uplift forces on foundations.

• Allow for cost-effective construction by reducing the need for rigid framing.

• Improve the performance of rectangular-plan buildings.

• Utilize external columns as part of the lateral load-resisting system.

Disadvantages

• May reduce usable floor area (if placed at multiple levels).

• Can complicate construction and erection processes.

• Need careful placement and design (often at mechanical floors).

Engineering Necessity

Outriggers are essential in modern high-rise design for maintaining structural safety, especially under lateral loads. They ensure balance, reduce tipping risks, and meet safety standards, particularly in seismic and high-wind zones.

Key Research Insights

• Shareef et al. (2022): Studied 36- and 50-storey buildings with outrigger walls in seismic zone V using ETABS. Found outriggers significantly improve performance under lateral loads.

• Singh et al. (2022): Analyzed G+9 irregular composite frames and confirmed the benefit of belt trusses and outriggers in improving base shear, drift, and displacement.

• Kamath et al. (2022): Conducted parametric studies on 40-, 60-, and 80-storey buildings. Found outrigger arm length has the greatest effect on improving system performance.

• Alavi et al. (2021): Proposed a stiffness-based design method for outrigger placement using uniform deformation principles, validating it through hand calculations and showing accurate performance predictions.

Conclusion

1) Outriggers, particularly in double-sided configurations with shear walls, substantially enhance seismic performance in tall RCC buildings. 2) Performance gains are evident across stiffness, displacement, drift, and shear metrics, with maximum reductions in displacement exceeding 34% in the studied case. 3) Integration with shear walls further amplifies benefits, leveraging both systems’ stiffness contributions. 4) Response Spectrum Method analysis confirms that outrigger systems can meet Indian seismic code requirements with improved efficiency compared to conventional framing. 5) Future research should explore optimal outrigger height placement under Indian seismic spectra, compare conventional vs. virtual outriggers experimentally, and assess cost-benefit trade-offs for varying building geometries.

Copyright

Copyright © 2025 Abu Talha Anwar Pasha Deshmukh, Dr. Durgesh H. Tupe. 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.