Core
Walls around stairs and services can provide substantial lateral stiffness. A core is not simply an empty elevator shaft.
Look inside the height
Explore how a tower carries loads and moves people. Select a layer in the diagram, then see how the actual top 10 solve these problems.
An explanatory section of a generic core-and-outrigger tower, not an as-built drawing. The two outrigger bands, lift stops, pile lengths and floor count are illustrative. Burj Khalifa’s buttressed core and One World Trade Center’s moment frame use different arrangements. Structural principles & sources ↗
Outriggers
Deep members connect a core to perimeter columns, engaging a wider structural lever arm. They are one strategy, not a feature of every tower.
Occupied floors
Floor diaphragms collect horizontal forces and transfer them into the lateral system. Occupied floors stop below many architectural crowns.
Elevator zones
Separate low, middle and high zones can reduce the number of shafts that continue through the full height. Transfer lobbies connect different services.
Foundations
A raft spreads load, while piles can transfer it into deeper ground. Foundation type depends on geology, settlement and the tower above.
All systems shown
FROM PRINCIPLE TO PROJECT
Ten towers, different answers
The diagram above remains a generic teaching model. The sourced notes below describe the selected building’s actual system and construction.
Burj Khalifa: Three wings that buttress one another.
Structural system & load path
SOM arranged three concrete wings around a six-sided core. Each wing braces the other two, while the central cell supplies torsional stiffness. The setback geometry aligns columns above with walls below, avoiding disruptive transfers as the floor plate reduces. Gravity and lateral resistance follow the same disciplined geometry.
Project engineering source ↗Foundations & durability
A reinforced-concrete mat, 3.7 metres thick, distributes the tower load to bored piles 1.5 metres in diameter and 43 metres long. The mat was cast in four pours totalling 12,500 cubic metres. Low-permeability concrete forms part of the foundation durability strategy.
Project engineering source ↗How it was built
The Samsung C&T, Six Construct and Arabtec joint venture had to coordinate cranes, labour and material supply vertically. BESIX reports concrete pumping to 585 metres and cycles reaching two floors per week. Special mixes and predominantly night-time pours addressed temperatures exceeding 45°C.
Project engineering source ↗Wind, facade & services
Successive setbacks change the shape the wind encounters, reducing coherent vortex formation. The envelope uses silver-coated glazing to limit solar gain. Mechanical equipment is distributed through double-height service floors; the design also collects air-conditioning condensate for reuse. The steel spire was assembled inside the building and hydraulically raised into position.
Project engineering source ↗Merdeka 118: High-performance concrete, a stiff core and a carefully engineered spire.
Core, mega-columns & outriggers
High-performance concrete in the core and mega-columns works with three sets of three-storey-deep outriggers. Arup describes a mix combining high stiffness, strength and workability. This allowed smaller structural members while maintaining resistance to wind loading.
Project engineering source ↗Excavation beside national landmarks
A circular cofferdam retained the excavation using hoop action. Its self-supporting geometry removed the need for internal struts or ground anchors. Geotechnical monitoring tracked settlement and lateral movement near Stadium Merdeka and Stadium Negara.
Project engineering source ↗How it was built
Samsung C&T and UEM Builders delivered the tower as SUJV. Arup and the contractor co-developed a pumpable concrete mix for high-elevation placement, balancing flow, stiffness and heat of hydration. This made concrete technology central to the construction strategy, rather than simply specifying greater strength.
Project engineering source ↗Spire dynamics & fatigue
The slender spire uses a three-dimensional space truss. Aeroelastic wind-tunnel testing established its wind response, and fatigue analysis examined connections under repeated daily wind events. Strength alone was insufficient: vibration and accumulated cyclic damage were explicit design concerns.
Project engineering source ↗Shanghai Tower: A twisting envelope around a core-and-outrigger structure.
Core, outriggers & super-columns
A concrete core approximately 27 metres square connects through outrigger trusses to super-columns. The core and perimeter act together to resist wind and seismic effects. The foundation uses 1,079 deep piles. The visible twist belongs to the facade geometry; the structural organisation remains comparatively regular.
Project engineering source ↗Aerodynamics & occupant comfort
Thornton Tomasetti reports a 24% wind-load reduction from refinement of the tower form. A double-hung pendulum tuned mass damper further limits wind-induced movement. These address different problems: shaping reduces excitation, while the damper controls the response experienced by occupants.
Project engineering source ↗How it was built
Shanghai Construction Group used bottom-up construction for the tower inside a circular diaphragm wall, with top-down construction around the podium. A 6-metre foundation slab required a continuous mass-concrete pour. An integrated climbing platform combined scaffold, forms and supports. The contractor reports C60 concrete pumping to 582 metres, with other mixes pumped higher.
Project engineering source ↗Double-skin facade
Gensler organised the tower as stacked vertical communities, with atrium spaces between the inner and outer enclosures. This creates a buffer between occupied rooms and the weather. The facade had to accommodate twisting geometry while remaining coordinated with floor edges and supporting structure.
Project engineering source ↗Makkah Royal Clock Tower: A concrete tower that becomes progressively lighter toward its clock and crown.
A changing structural system
The lower tower uses reinforced concrete. Above approximately 347 metres, steel-concrete composite construction reduces self-weight; above 513 metres, the upper structure is steel. The lateral system changes from core walls to a lighter trussed tube, following the demands of the increasingly slender crown.
Project engineering source ↗The clock is a structural project
SL Rasch was commissioned after the underlying hotel towers had already been structurally calculated. The clock addition therefore had a weight constraint. Four V-shaped supports carry the upper assembly, converging into the spire structure. Composite steel and concrete sections provide capacity while controlling dead load.
Project engineering source ↗How it was built
The specialist engineering scope extended beyond the permanent frame to erection planning, fabrication quality control and temporary crane supports. Both internal and external climbing cranes required engineered bracing. The transition between concrete, composite and steel construction made connection detailing and erection-stage stability central to delivery.
Project engineering source ↗Lightweight components at extreme height
The clock hands use carbon-fibre shells, with stiffness supplied by their skins. The 23-metre crescent is a self-supporting fibre-composite structure. Using these materials limits the mass of large components exposed to wind at the top of the building.
Project engineering source ↗Ping An Finance Centre: Eight super-columns and a braced perimeter share the lateral work.
Structural system & load path
A composite concrete core connects to eight super-columns through steel outriggers. Seven double-layer belt-truss zones tie the perimeter together at mechanical and refuge levels. Large diagonal members connect these zones on each face, producing an exterior braced system in addition to the core.
Project engineering source ↗Seismic design
Thornton Tomasetti used nonlinear dynamic time-history analysis in the performance-based seismic review. This evaluates the response to earthquake records beyond a purely elastic force check. The design was developed through multiple alternatives and scrutiny by a seismic expert panel.
Project engineering source ↗How it was built
CSCEC used an integrated construction platform that carried a large tower crane and climbed with the works. The platform coordinated surveying, steel erection, reinforcement fixing, formwork and concrete placement. Combining these operations reduced separate handling steps and provided a working area for several processes at elevation.
Project engineering source ↗Architecture & usable floor plates
KPF and local design institute CCDI organised the headquarters around more than 100 floors of offices, with retail and conference space in the podium. The public atrium and connections to adjacent properties and transit address circulation at the base, where a supertall building meets the city.
Project engineering source ↗Lotte World Tower: Long-span floors carried between eight concrete mega-columns.
Structure & floor planning
Concrete core walls and eight mega-columns form the primary system, linked by outriggers and belt trusses. The office and officetel levels use long-span spandrels up to 24.5 metres between columns. At corners, these members cantilever approximately 14 metres while following the curved floor edge.
Project engineering source ↗Deflection, vibration & transfers
Those long corner cantilevers made floor deflection and vibration important serviceability checks. Belt trusses manage changes in column layout between uses: hotel columns transfer toward the mega-column arrangement below, and the upper diagrid lantern connects through another structural transition.
Project engineering source ↗How it was built from the ground up
Lotte E&C reports a foundation mat 72 metres square and 6.5 metres thick. That massive concrete base supports a mixed concrete-and-steel superstructure. Construction then had to coordinate core and mega-column work with the long-span floor framing and the transfer zones between the tower’s different uses.
Project engineering source ↗Form as wind engineering
The taper helps reduce wind loading, but creates changing geometry and structural spans over the tower height. LERA studied several perimeter arrangements before the owner selected long-span spandrels for the lower occupied zones. The choice traded simpler intermediate supports for more open floor plans.
Project engineering source ↗One World Trade Center: A high-strength concrete core paired with a ductile steel perimeter.
Core and perimeter work together
The reinforced-concrete core works with a ductile perimeter steel moment frame to resist gravity, wind and seismic effects. Floor beams span from the core to the exterior, keeping office areas comparatively open. This hybrid differs fundamentally from the perimeter-tube arrangement of the original towers.
Project engineering source ↗Materials & member size
WSP reports core concrete reaching 14,000 psi, approximately 97 MPa. Greater strength helped control wall thickness, structural weight and rentable-area loss. Its concrete mix replaced more than half the cement content with industrial by-products. The project also used substantial recycled steel.
Project engineering source ↗How it was built
Tishman coordinated the reinforced-concrete core and steel frame. ArcelorMittal supplied 12,500 tonnes of structural steel, primarily large Grade 65 sections. The resulting construction combines cast-in-place walls with fabricated beam-and-column assemblies, rather than relying on a single structural material throughout.
Project engineering source ↗Egress integrated into the structure
The core encloses access stairs and a dedicated stair for first responders. Enhanced fireproofing, redundant water supplies and protected circulation were integrated into the structure and floor planning. These are specific design features of this building, not a claim that any tower is immune to fire or impact.
Project engineering source ↗Guangzhou CTF Finance Centre: Structural planning shaped by offices, residences and a hotel in one tower.
Core, mega-columns & foundations
The developer’s 2014 technical paper describes a 32-metre square core and eight concrete-filled steel-tube mega-columns on mat and pad foundations bearing on rock. Four outrigger levels and six double-layer belt-truss sets link the structure at mechanical and refuge floors. C80 concrete reduced required wall thickness.
Project engineering source ↗Stacked uses & changing floor plates
KPF organised four main transition points as the programme moves upward from offices to residences, hotel and sky lobby. The changes in volume correspond to different occupancy needs. The tower also connects to transport below ground and neighbouring buildings by pedestrian bridges.
Project engineering source ↗How it was built: delayed connections
The construction sequence delayed final outrigger connections to the mega-columns. This allowed for differential shortening between the columns and core, limiting locked-in stresses. The developer’s paper also records wind-tunnel studies and a 1:40-scale shaking-table test used to assess the proposed seismic behaviour.
Project engineering source ↗Envelope & building services
The terracotta piers shade the glazed facade while preserving views. KPF also identifies high-efficiency chillers and heat recovery as part of the environmental strategy. At this scale, shading, cooling loads and space allocation for plant are interdependent architectural and engineering choices.
Project engineering source ↗Tianjin CTF Finance Centre: A curved mega-frame tuned for stiffness, ductility and lower material use.
An integrated structural form
SOM’s composite structural system follows the architectural massing. Diagonal zones increase lower-level stiffness; more vertical zones provide ductility for seismic energy dissipation. Gravity loads help oppose lateral overturning. The frame geometry is doing structural work as well as shaping the facade.
Project engineering source ↗Wind response & material efficiency
The taper, porous crown and wind openings improve aerodynamic performance. SOM reports that structural optimisation reduced steel demand and seismic mass enough to avoid a supplemental damping system. This is a project-specific outcome, not a universal advantage over towers that use dampers.
Project engineering source ↗How it was delivered
China Construction Eighth Engineering Division acted as main contractor, with ECADI responsible for the structural documents as engineer of record. SOM links reduced steel quantities to savings in construction time and cost. Coordination of composite structural members and the curved enclosure was part of the integrated design approach.
Project engineering source ↗Floor spans follow the programme
Larger office plates occupy the lower building, while apartments and hotel rooms use smaller plates higher up. This arrangement informed the taper and structural spans. Separate lift systems and sky lobbies handle the differing access requirements of the three principal uses.
Project engineering source ↗CITIC Tower: A tower that widens at the top, engineered for a demanding seismic setting.
Mega-frame & concrete core
A fully braced perimeter mega-frame and central concrete core form the lateral system. Composite mega-columns and steel-plate concrete walls provide capacity without excessive member size. The perimeter’s concrete-filled steel box sections and belt trusses create an additional line of resistance in Beijing’s high seismic setting.
Project engineering source ↗A widening crown changes the problem
The plan narrows from 78 metres at the base to 54 metres around 385 metres up, then expands to 70 metres at the top. Arup connected parametric models to structural analysis to evaluate more than 800 options, coordinating column centrelines, facade geometry and the changing mass distribution.
Project engineering source ↗How it was built
An integrated steel work platform sat on top of the concrete core and was jacked upward as construction progressed. It carried multiple working levels and reduced reliance on conventional crane operations. The Institution of Structural Engineers singled out this construction system alongside the permanent structural design.
Project engineering source ↗Seismic behaviour & fire strategy
Arup developed seismic and fire strategies as part of the design scope, including structural fire analysis and evacuation planning. Large connected lobby areas and the densely occupied observation deck required particular attention. The design combined structural resistance with circulation and compartment planning.
Project engineering source ↗