In this blog post, we’ll explore how buildings withstand earthquakes and strong winds, the core principles of seismic design, and the conditions under which these principles are applied.
Why can some super-tall buildings withstand strong earthquakes and winds?
The Burj Khalifa, one of the world’s tallest buildings, stands at a total height of 828 meters. This height is more than three times that of the 63 Building in Yeouido and is comparable to the height of Mount Bukhan, one of Seoul’s taller mountains. What’s remarkable is that such a massive structure was designed to withstand earthquakes of magnitude 6.0 or higher and strong winds reaching 36 meters per second along the coast. An earthquake of magnitude 6.0 or higher, if it occurs in the middle of a city, is strong enough to cause many buildings to collapse, and winds of 36 m/s are typhoon-level winds powerful enough to blow people or large objects away. Seismic design is the key to ensuring the building does not collapse even under such extreme conditions.
Principles and Analysis Methods of Seismic Design
When an earthquake or strong winds occur, both the ground supporting the building and the building itself shake. Seismic design refers to the process of designing structures to prevent complete collapse in such situations and to minimize loss of life. At first glance, one might think that simply making the building very strong and rigid would suffice; however, considering economic feasibility and practicality, building structures solely for strength is inefficient and imposes a significant cost burden. Therefore, a more effective approach is to design the structure to possess a certain degree of ductility.
Ductility is the ability of a structure to withstand large loads without severe failure, allowing for significant deformation while maintaining structural integrity. In seismic design, the structure dissipates vibration energy through nonlinear behavior, thereby preventing total collapse and minimizing damage. In other words, structural safety is ensured by absorbing and dispersing energy.
The primary methods for evaluating and designing seismic safety are the equivalent static analysis method and the dynamic analysis method. The equivalent static analysis method involves performing structural analysis by applying a static horizontal force of the same magnitude as the horizontal force that could be generated by an earthquake to the building. Simply put, it treats the seismic force as a single constant force and analyzes how the building responds to it.
Dynamic analysis is a method of evaluating seismic safety by calculating a building’s dynamic response to seismic vibrations. Since each building has its own natural period and characteristics and thus reacts differently to earthquakes, dynamic analysis involves analyzing these individual responses by considering actual time-varying seismic waves. It is easier to understand if you think of it as a principle similar to how three trees sway differently in the same wind.
Five Conditions Required for Seismic Design
Simply applying seismic design does not guarantee that every building will be safe during an earthquake. For a building to properly demonstrate seismic stability, it must meet five conditions.
First, the building must possess sufficient ductility appropriate for its intended use and function. If we compare a tree that bends in the wind to one that breaks, the latter lacks sufficient ductility. Similarly, even if a building possesses ductility, it may ultimately fail to withstand heavy loads and collapse if its basic ductility is not ensured.
Second, there must be limits on the amount of deformation caused by earthquakes or wind. Consider a baby bird nesting in a tree. Just as the baby bird in the nest could fall and be endangered if the tree sways too violently, safety can only be ensured by limiting the relative deformation of living spaces, given that people are inside the building. Furthermore, since ductility has its limits, excessive deformation can cause the structure to fail and collapse.
Third, major structural elements such as columns and walls must be appropriately positioned and constructed to be strong enough to withstand such forces. Even if the overall structure is durable, the entire building could collapse if the columns or walls supporting it are weak; therefore, special attention must be paid to the stability and placement of these components during design.
Fourth, the characteristics of the ground must be thoroughly understood, and a foundation appropriate for those conditions must be selected. If the ground supporting the building consists of soft clay layers, safety can be compromised due to ground subsidence or tilting, no matter how well the building is designed. As seen with the Leaning Tower of Pisa, weak ground affects the entire structure; therefore, securing firm ground or selecting a foundation method suited to the conditions is crucial.
Fifth, materials and reinforcements with excellent seismic resistance and performance must be used. For example, by appropriately placing highly ductile rebar within concrete or installing vibration-absorbing reinforcement devices—that is, by ensuring both resistance and ductility through materials and reinforcement methods—resistance to earthquakes and strong winds is significantly improved. Only when these five conditions are met can the objectives of seismic design be properly achieved.
Earthquake Risk in Korea and the Current Status of Seismic Design
In the past, Korea was perceived as a country relatively safe from earthquakes, but recently, awareness of earthquake risks has been growing. According to data from the Korea Meteorological Administration, 79 earthquakes with a magnitude of 2.0 or higher occurred on the Korean Peninsula and in surrounding waters in 2025. Although this figure is lower than the 87 earthquakes recorded in 2024, it exceeds the annual average of approximately 73 earthquakes since 1999, when digital monitoring began. Therefore, it is no longer accurate to view South Korea as a region completely free from seismic risk. In particular, the importance of earthquake preparedness has been further highlighted by events such as the 2016 Gyeongju earthquake, the 2017 Pohang earthquake, and the 2024 Buan, Jeonbuk earthquake. Since the scale of damage caused by a single strong earthquake is far greater than the frequency of earthquakes, preventive measures and ensuring the safety of structures are of the utmost importance. While the status of seismic design has improved compared to the past, challenges remain. According to the Ministry of the Interior and Safety, as of 2025, the seismic retrofit rate for existing public facilities has improved to 82.7%. This represents more than a doubling compared to the 37.3% recorded in 2011. However, the seismic retrofit rate for private buildings remains below 20%, leading to concerns that many structures are not sufficiently prepared for earthquakes. If a strong earthquake of magnitude 6.0 or higher were to occur, buildings not designed to be earthquake-resistant would be highly likely to suffer various damages, such as cracks, collapse, and fire. Therefore, it is necessary not only to strictly enforce seismic design standards for new buildings but also to continuously expand seismic retrofitting for existing structures. The most effective way to reduce earthquake damage is not post-disaster recovery but preemptive preparedness, and seismic design is one of the key measures for achieving this.
