Skyscrapers Series · @JayStructure
Outrigger Systems in Supertall Buildings
How the world’s tallest skyscrapers resist wind — and why the solution involves tying the core to the columns with giant steel arms
Supertall Engineering
Jay Sah
Site Engineer · High-Rise Construction · Sydney
At 300 metres above the ground, the wind does not feel like it does at street level. It is not a gust — it is a sustained, dynamic force that pushes and pulls at the building constantly. Without the right structural system, a tower this tall would sway metres at its tip. The occupants would feel it. The structure would fatigue. Cladding would fail.
The outrigger system is the engineering answer to this problem. It is how the Burj Khalifa, the Shanghai Tower, the Petronas Towers, and virtually every supertall building ever constructed manages to stand up against the wind — and stay comfortable enough for people to live and work inside.
The Wind Problem at Height
Without structural intervention, a 400m tower
could sway over 1 metre at its tip.
Human perception of sway begins at around 10–15mm/s. Outrigger systems reduce sway by 25–40% compared to a core-only structure.
What is an Outrigger System?
An outrigger system connects the central core wall of a supertall building to its perimeter mega-columns using massive steel or concrete arms — the outriggers — that typically span the full width of the building at one or more levels. These outrigger levels are often called mechanical floors or refuge floors and occupy one to three full storeys of the building height.
Outrigger System Components
🏙️
Core Wall
Central RC spine — primary lateral resistance
🔧
Outrigger Arms
Steel trusses spanning from core to perimeter
⚪
Mega Columns
Large perimeter columns — receive outrigger forces
🔗
Belt Trusses
Ring beams connecting all perimeter columns at outrigger level
How It Resists Wind
Without outriggers, a core wall resists wind as a pure vertical cantilever. The core takes all the bending. The columns contribute nothing to lateral resistance — they are just carrying gravity loads. This is inefficient. The core must be enormous to resist all the overturning alone.
When outriggers are added, the moment from wind is converted into a couple — a tension force in the leeward columns and a compression force in the windward columns. The core no longer has to resist the full overturning moment alone. The perimeter columns are now engaged. The whole building works together as a structural system.
Wind Resistance Comparison
Core: 100%
Core: ~65%
Core: ~50%
Outriggers reduce the bending demand on the core — engaging the full perimeter of the building in wind resistance
Real Buildings — Real Outrigger Systems
Burj Khalifa
828m · Dubai
Buttressed core with Y-shaped plan. The three wings act as outriggers to each other. No traditional outrigger trusses — the geometry IS the system.
Shanghai Tower
632m · Shanghai
Eight outrigger levels connecting an inner core to a mega-column perimeter frame. Plus a 120-tonne tuned mass damper at the top.
Taipei 101
508m · Taipei
Eight super columns connected to a central core plus a 660-tonne tuned mass damper — the most visible in the world, hanging visibly in the building interior.
The Construction Challenge
Building an outrigger system is one of the most logistically complex operations in high-rise construction. The outrigger trusses are fabricated from heavy structural steel sections — individual members weighing 30 to 80 tonnes — that must be lifted by the tower crane to heights of 200 metres or more and connected with precision.
Outrigger Level Takes 2–4 Months
Each outrigger level requires its own sub-programme. Steel erection, concrete encasement of connections, connection bolting, and structural inspections all happen while the rest of the building continues around it. The outrigger level is essentially a building within a building.
Delayed Connection — The Key Strategy
Outrigger arms are often intentionally left disconnected from the perimeter columns during construction — and only fully connected after a large portion of the building above has been completed. This prevents the dead load of all those floors from locking differential shortening stresses into the outrigger connections. Timing of this final connection is a critical structural engineering decision.
Column Shortening — The Hidden Problem
Concrete columns shorten over time under sustained load — a combination of elastic deformation, creep, and shrinkage. Over a 400-metre building, the difference in shortening between the core and the perimeter mega-columns can be 50 to 80mm. This must be accounted for in the outrigger connection design — otherwise the outriggers will try to resist the differential movement and generate forces they were not designed to carry.
Key Numbers — Outrigger Systems
40%
reduction in core bending demand
80t
max single steel member weight
2–4
outrigger levels per supertall
80mm
max differential column shortening
The Reason Supertalls Can Exist
Without outrigger systems, the core wall would have to be so large to resist all lateral loads that it would consume most of the floor plate — leaving no usable space. The outrigger system is what makes supertall towers architecturally viable. It distributes the wind resistance across the entire structural perimeter of the building.
Every skyline you see — Dubai, Shanghai, New York, Kuala Lumpur — is filled with buildings that stand because an engineer somewhere designed a system of steel arms connecting a concrete core to a ring of giant columns, and then figured out exactly when to bolt those connections permanently in place.
Watch the full outrigger system breakdown
I cover the Burj Khalifa, Shanghai Tower and Taipei 101 structural systems in detail on the @JayStructure channel.
Supertall Buildings
Wind Engineering
Structural Engineering
Burj Khalifa
Skyscrapers