How supertall towers are designed for earthquakes

Two loads, two strategies

Wind and earthquakes both push a building sideways, but they do so in very different ways. Wind is a pressure applied to the outside over minutes or hours, and it can be measured and modelled with reasonable confidence. An earthquake shakes the ground beneath the building, and the structure responds to that motion through its own mass and stiffness. The forces depend on how the building moves as much as on the ground shaking itself. [1]

That difference changes the design goal. Against wind, a building is usually kept stiff so it barely moves. Against a strong earthquake, trying to make a building rigid can attract larger forces. Instead, engineers often want a structure with enough strength and, just as importantly, enough ductility: the ability to deform well beyond its elastic range without collapsing. [1]

The two loads also arrive with different frequency content. A tall, flexible building tends to have a long natural period, and ground motions that emphasise longer periods can be particularly demanding. Seismic design for a supertall tower is therefore tailored to the soil, the distance to active faults and the period of the structure, not applied as a single standard recipe. [2]

Ductility and capacity design

Ductility is the capacity of a member or a connection to yield, bend and stretch without breaking. In a well-detailed steel frame, the beams are allowed to form plastic hinges at their ends while the columns and connections remain strong enough to hold the frame together. In reinforced concrete, ductility comes from closely spaced stirrups and careful anchorage of the reinforcement, which keep a cracked section from failing suddenly. [3] [4]

Engineers control where the damage happens through a principle called capacity design. They choose a ductile element to act as the fuse, then design the surrounding elements to be stronger than that fuse, so that the building has a predictable way to absorb energy and does not fail in a brittle manner elsewhere. The goal is not to prevent all damage in a severe earthquake but to keep the structure stable and the occupants safe. [1]

Shear walls, cores and coupling beams

The reinforced concrete core that serves the lifts and stairs in a supertall tower is also a highly effective seismic element. A shear wall resists horizontal force through its own in-plane stiffness, and a closed core is a strong and stiff shape in both directions. Where openings for doors are needed, the wall is divided into piers connected by coupling beams, which can be detailed to yield and absorb energy. [5]

In many tall buildings the core is designed to carry most of the earthquake force, working with an outrigger system that engages the perimeter columns. The columns add stiffness and help resist overturning, while the core provides the ductile, energy-absorbing behaviour. This division of labour is one reason core-and-outrigger systems appear so often in seismic regions as well as in windy ones. [6]

Dampers: turning motion into heat

A building can be given extra energy-absorbing capacity by adding dampers. Viscous dampers use a piston moving through a fluid to convert motion into heat, much like a shock absorber in a car. Viscoelastic dampers use the shearing of a polymer layer. Both add damping without adding much stiffness, so they reduce movement without attracting more force, which is exactly what is wanted in a strong earthquake. [1]

A different approach is the buckling-restrained brace, a steel brace that is allowed to yield in both tension and compression inside a restraining tube. Unlike an ordinary brace, it does not buckle, so it can absorb energy steadily in both directions. Dampers and yielding braces are often placed in the core or in dedicated bays, where they can be inspected and, if necessary, replaced after a major event. [4]

Base isolation: when it is used and when it is not

Base isolation puts flexible bearings between the building and its foundation so that the ground can move while the building stays relatively still. Elastomeric bearings, lead-rubber bearings and friction pendulum bearings lengthen the effective period of the structure and add damping. The approach is widely used for hospitals, data centres and historic buildings, where keeping the contents and the structure undamaged is the priority. [7]

For very tall buildings the picture is more complicated. Isolation requires room to move, sometimes half a metre or more, and a tall tower can develop uplift and large overturning forces at its bearings. Isolating a light or very slender structure can also make it too flexible for comfort in everyday wind. For these reasons, base isolation is more common in low and mid-rise structures and in special tall buildings than in the tallest towers. [7] [2]

Where isolation is not practical, engineers get the same benefit in other ways, by adding damping devices within the structure, by detailing the core and frame to be ductile, and by designing for the specific ground motion expected at the site. [7]

Performance-based design

Because a supertall tower is not covered neatly by standard code tables, seismic design for these buildings often uses performance-based methods. Instead of following a single prescription, engineers define the performance the building must achieve at several levels of shaking, from frequent small events to rare severe ones, and then demonstrate through analysis and testing that the structure meets those targets. [1] [2]

The analysis includes the non-linear behaviour of the structure, the soil conditions and the expected ground motions, often represented by a suite of recorded and simulated earthquake records. Full-scale or large-scale testing of critical components, such as a damper or a beam-to-column connection, may be used to confirm that the assumed behaviour is real. [8]

Soil, site and long-period shaking

The ground under a building is not a fixed platform. Soft soils can amplify certain frequencies of shaking and lengthen the period of the motion that reaches the structure, and deep sedimentary basins can trap and amplify waves in ways that make distant earthquakes damaging to tall buildings. Mexico City is a well-known example, where soft lake-bed soils amplified long-period shaking far from the earthquake source. [1]

Because tall, flexible buildings have long natural periods, they can resonate with this long-period motion. Seismic design for a supertall tower therefore begins with a site-specific study of the soil profile and the nearby faults, producing ground motions that represent the shaking the building is actually likely to experience rather than a single generic value from a map. [2]

Case: tall buildings in seismic zones

Taipei 101 stands in a region of high seismic hazard, and its design combines a stiff, ductile concrete core with a massive tuned mass damper near the top. The damper is best known for controlling wind-induced sway and the comfort of occupants, while the ductile core and its connections address the earthquake demand. The building shows how the wind and seismic strategies are developed together rather than separately. [9] [10]

For towers in places like Tokyo, Taipei, Istanbul or the west coast of the Americas, seismic design is part of the everyday engineering, not an afterthought. The common thread is a structure that is strong enough to resist the load, stiff enough to be comfortable, and ductile enough to deform, absorb energy and survive the rare event for which it was designed. [1] [2]

Resilience: what happens after the shaking

A modern seismic design goal is often broader than life safety. A building that survives an earthquake without collapsing but has to be demolished afterwards is a poor outcome for a city, and for a supertall tower the cost of closure can rival the cost of the structure. Resilience treats the building as something that should be usable again, or at least repairable, after a strong event. [8]

That idea changes the design. Replaceable dampers, connections that can be inspected, and a clear plan for what may yield and what must stay elastic all make repair easier. Some projects go further and target immediate reoccupancy after a moderate earthquake. The structural system is chosen not only for its strength but for how gracefully it will behave and how readily it can be brought back into service. [1]

Takeaways

Earthquakes demand a different response from wind. Rather than pure stiffness, engineers design for ductility, ensuring the structure can deform and absorb energy without collapsing. Capacity design keeps the yielding in chosen locations and protects the rest. [1]

Concrete cores and shear walls carry much of the force, dampers and yielding braces add energy absorption, and base isolation suits low and mid-rise buildings more often than the tallest towers. For supertall buildings, performance-based design ties these tools to the specific shaking expected at the site. [7] [2]