1. Introduction
Seismic design involves designing structures that can withstand the seismic forces anticipated in the near future due to earthquake activity.
However, just as we cannot predict the future, we cannot accurately determine the characteristics of future earthquakes. This is because, much like the unique features of individual faces, the characteristics of seismic waves vary significantly depending on the location of the earthquake or the observed site.
Nevertheless, we have only identified general trends based on the analysis of various seismic waves observed on Earth until now.
The characteristics of seismic waves are influenced by the following factors, resulting in distinct features for each.
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The size or shape of faults at the epicenter or the destructive form of rocks in the epicentral area.
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The influence caused by the propagation path from the epicenter to the observation point.
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The impact of amplification characteristics in the shallow subsurface soil layers at the observation point.
In order to intuitively understand the impact of the frequency characteristics of seismic waves on structures, it is necessary to first comprehend the phenomenon of resonance.
Commonly, we might think that tall buildings, which are easily swayed by everyday vibrations like wind, are more vulnerable to earthquakes, while shorter buildings are safer. However, in seismic-prone regions worldwide, such as Tokyo in earthquake-prone Japan or California in the United States, many skyscrapers have been constructed.
How is it possible to build numerous skyscrapers in earthquake-prone areas?
The answer lies in the concept of response spectrum, which can be explained by the resonance phenomenon between the frequency characteristics of seismic waves and the objects that vibrate due to earthquakes.
In other words, earthquakes have the property of gently shaking flexible objects with weak force, while strong objects are struck with a stronger force. By designing structures flexibly, not to resist seismic forces but to avoid them, the theoretical background is established for the construction of tall buildings and large bridges, such as cable-stayed bridges, in earthquake-prone areas.
The concept of seismic isolation involves strategies where rigid lower structures deceive earthquakes as if they were longer-period structures. Similar to the strategy of avoiding confrontation and evading the enemy in military tactics, the concept in seismic design, particularly in the short-period range, is about avoiding direct confrontation with seismic forces.
However, it is important to exercise caution regarding the durability of the seismic isolation devices, as there is limited experience with earthquakes in this regard.
2. Responce Spectrum and resonance
2.1 What is Responce Spectrum?
Generally, when we hear the term "spectrum," the first concept that may come to mind is the beautiful seven colors of the rainbow revealed through a prism by sunlight. Sunlight, when viewed directly, is perceived only as brightness without any discernible colors, but when passed through a prism, it decomposes into seven different colors based on frequency.
Similarly, when examining the seismic waves recorded in the time history of seismic waves that represent the size of seismic motion, relatively simple characteristics such as the duration and maximum acceleration of an earthquake can be easily identified. However, it is challenging to accurately comprehend the frequency components included in seismic waves.
Therefore, similar to using a prism to understand the frequency components of light, mathematical tools are employed to decompose the characteristics of seismic waves into frequency components.
One of these analytical methods is the response spectrum, and it is generated through the following process:
After applying a forced displacement to an object, when released, the object undergoes vibration due to the restoring force that tends to return it to its original position and the inertial force that tends to keep it in place. The period during which the object vibrates is referred to as the natural period of the object and varies based on the material and shape of the object. The phenomenon of consuming energy through heat or sound as the object vibrates is called damping.
The response spectrum is the result of analyzing the frequency components of seismic waves through the vibration of an object with a specific period and damping. A schematic representation of its construction is shown in Figure-1.
Considering a plate as the ground and shaking it like seismic motion, the single-degree-of-freedom systems will vibrate according to their respective natural frequencies. The response spectrum is a graph that represents the measured responses of each single-degree-of-freedom system over time, with the natural frequency on the X-axis and the maximum response corresponding to the natural frequency on the Y-axis.
The shape of the spectrum has many undulations depending on the frequency characteristics of seismic waves, and the outstanding period, which corresponds to the period with significant responses, is referred to as the Predominant Period. As damping increases, the characteristics of the period decrease, and the undulations become more gradual.
While the shape of the spectrum varies with seismic waves, the analysis of spectra from seismic waves observed worldwide has revealed that spectra generally exhibit similar properties. A simplified representation of the general tendencies of spectra is shown in Figure-2.
When examining the acceleration response spectrum directly related to the magnitude of seismic forces, it is observed that up to a certain short period, the spectrum generally maintains a constant value. However, as the period increases, there is a tendency for the response to rapidly decrease.
A significant response at a particular period implies that the seismic wave contains a substantial component of that period. Conversely, a smaller response indicates that there is a lesser inclusion of components at that period in the seismic wave.
2.2 The phenomenon of resonance
So, why is the decomposition of seismic wave components by period important, not only in terms of the magnitude of maximum acceleration but also in terms of periods?
This is because the damage to structures caused by earthquakes is significant not only in relation to the size of the earthquake but also when the periods of the seismic waves coincide with the natural periods of the structure, resulting in resonance.
Let's consider a few examples from our daily lives to understand this resonance phenomenon better.
During elementary school, you might have performed an experiment where two sound forks of the same size and shape were placed apart, and when one of them was set into vibration, the other fork started vibrating as well.
This phenomenon occurs because the vibrational energy generated by the vibrating tuning fork is transmitted to the other tuning fork through the medium of air. Tuning forks of similar size and shape, capable of efficiently absorbing the vibrational energy of the air, can easily exchange vibrational energy, leading to resonance. On the other hand, tuning forks of different sizes and shapes cannot effectively absorb vibrational energy, preventing the occurrence of resonance.
Thus, the phenomenon of easily exchanging vibrations occurs only when the natural frequencies of the two objects are similar.
In this way, when the vibrating periods of an object applying external force and another object receiving external force are close, resonance occurs. Considering the important issue we face in seismic design, let's think about the resonance relationship between the seismic force acting on a structure and the structure itself.
For example, if two buildings with significantly different numbers of stories are constructed in close proximity, the lower building, due to its structural characteristics, may have a shorter natural period, while the taller building may have a longer natural period.
If, for instance, an earthquake with a characteristic of strong short-period components and weak long-period components occurs in this region, due to the resonance phenomenon between the earthquake and the structure, there is a high possibility that the lower building will be damaged, while the taller building will be relatively safe.
Conversely, if an earthquake with strong long-period components and weak short-period components occurs, there is a high likelihood that the taller building will be damaged, while the lower building will be relatively safe.
In essence, the determination of a structure's seismic safety is more about whether there is resonance due to the coincidence of the seismic predominant period and the building's natural period, or whether there is a mismatch resulting in no resonance, rather than simply evaluating whether the building was constructed sturdily or poorly.
The seismic design of a structure must consider the frequency characteristics of seismic waves, and the importance of response spectra that represent the frequency characteristics of seismic waves lies in this consideration.
Therefore, predicting the occurrence of seismic events with specific predominant periods in the target site where a structure will be built becomes a crucial issue in seismic design. Unfortunately, or fortunately, we have not yet reached a precise conclusion on this matter. Currently, we are adopting foreign design standards or applying design criteria based on a rough understanding of the characteristics of the ground.
However, for seismic design suitable for South Korea, it is necessary to develop design response spectra reflecting the ground characteristics of the Korean Peninsula. Simply applying design standards from the United States or Japan may lead to results that differ significantly from the actual seismic damage and predictions.
3. The concept of Vibration Control Structure, Siesmic Resistance Structure, Seismic base isolation Structure
3.1 Vibration Control Structure
The term "Know the enemy and know yourself, and you can fight a hundred battles and win them all," similar to a tactical strategy, can be applied to earthquakes as adversaries seeking to protect our lives and properties. In dealing with the enemy known as earthquakes, it is crucial, first, to accurately understand their characteristics and, second, to consider our tactical approach, which involves the design of structures.
Looking at our tactical aspects in designing structures, we can consider different approaches such as creating resilient structures to withstand earthquakes, known as "seismic-resistant structures," or structures that avoid and do not resist seismic waves by escaping from the strong energy band of seismic waves, referred to as "base-isolated structures." Another approach is actively coping with earthquakes, known as "Vibration control structures."
To simplify these tactics, imagine being on a moving train and feeling vibrations. Older individuals inside the train might grab onto handrails to maintain their balance, while younger individuals use their legs to brace themselves and avoid falling. Applying this concept to maintaining balance in the human body, older individuals holding onto surrounding objects to stabilize themselves is akin to the installation of additional components (seismic walls) within a structure to withstand earthquakes, making it a seismic-resistant structure. On the other hand, younger individuals using their legs to brace themselves corresponds to structures equipped with facilities that apply artificial force in the opposite direction of the structure's vibrations to control the shaking – these are known as base shear structures.
The term "Vibration Control" encompasses a broad meaning, including the control of general vibrations (seismic or wind-induced) as well as typical vibration control. In terms of methods for base isolation, two main approaches can be considered.
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A method to suppress the vibrations of a structure by incorporating a detection capability within the structure itself to sense vibrations coming from external sources and the resulting vibrations within the structure. The structure autonomously possesses control mechanisms to respond to vibrations within the structure, whether originating internally or externally, aiming to mitigate and dampen the vibrations of the structure.
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A method of controlling a structure by momentarily adjusting the stiffness or damping of the structure in response to the characteristics of input vibrations, without exerting external or internal forced control on the structure.
The former involves calculating the ground vibrations input to a structure and its response, and then artificially applying control forces in the opposite direction to mitigate the vibrations. The latter involves immediately analyzing the frequency components of incoming vibrations to change the vibration characteristics of the structure, avoiding resonance.
However, while these methods are theoretically possible, there are practical risks. Even small errors in calculations by electronic computers can lead to the destruction of structures. There is also a disadvantage in that constant maintenance is required for the facilities to be prepared for unpredictable earthquakes.
Moreover, having large computers within the building and the need for various measuring instruments make these methods economically impractical for small structures. However, as structures become larger and new technologies develop, these methods are gradually becoming practical.
Vibration control structures, in this context, refer to an active concept aimed at overcoming earthquake damage by actively resisting seismic forces.
A base-isolated structure, or base-isolation structure, refers to a type of structure in which an isolator, such as rubber, is installed between the foundation and the structure. This is done to prevent the significant propagation of ground vibration energy to the structure. The isolation is achieved by either elongating the natural period of the structure or fundamentally blocking the transmission of seismic vibrations to the structure. This method is analogous to how magnetic levitation trains have no vibration, preventing seismic vibrations from being transmitted to the structure.
In addition, various methods can be considered to prevent earthquake damage, such as the following methods.
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A method to prevent seismic waves from reaching urban areas by installing a massive concrete layer underground, causing seismic waves to be reflected into the ground.
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A method of designing structures like ships on fluid surfaces, taking advantage of the fact that fluids, such as water, do not experience seismic forces.
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Another method involves preventing the occurrence of a major earthquake by artificially relieving the stress accumulated in bedrock layers through controlled explosions, similar to detonating atomic bombs.
However, these methods are still speculative and not currently feasible.
3.2 Seismic Resistance Structure
Generally, all structures on Earth are designed to withstand vertical loads such as Earth gravity. However, they are often vulnerable to horizontal loads such as wind or earthquakes.
For example, in the case of a bridge, it may withstand vertical loads like the weight of vehicles and the bridge deck, but horizontal loads caused by flooding, where the river water inundates the bridge deck, can lead to its easy destruction.
Nevertheless, there are bridges like a submerged bridge designed to withstand horizontal loads caused by river flooding. Similarly, seismic-resistant structures are designed to withstand horizontal loads, such as seismic forces.
In ancient times when societies were less developed and lacked the ability to consider horizontal loads like earthquakes or winds, structures would often collapse due to such loads, and the rebuilding process had to be repeated.
As society advanced and the economy grew, critical structures like nuclear power plants, high-rise buildings, and large bridges became susceptible to significant loss of life and property in the event of seismic damage. Therefore, seismic design for contingency planning has become essential for these structures.
Until the late 1970s, South Korea, with limited experience of earthquakes, did not incorporate considerations for horizontal forces like seismic forces in the design of civil and architectural structures, except for wind loads. It was only with the construction of nuclear power plants in the late 1970s that the concept of seismic design began to be introduced.
As rapid economic development took place, the need for seismic design became more apparent. In December 1986, the Building Act was revised, stipulating that structures should have a seismic-resistant design. Subsequently, the "Regulations on the Structure Standards of Buildings" were first established in 1988, providing systematic seismic design standards for buildings.
Recognizing the importance of seismic design for bridge structures, the concept of seismic design for bridges was introduced in the revised Road Bridge Standard Specifications in December 1992. In recent years, there has been a trend towards strengthening seismic regulations.
One significant difference in design considerations for long-span bridge structures in the longitudinal direction, as opposed to buildings, is the consideration of temperature expansion and contraction.
For bridge structures where seismic loads are not the dominant load condition, an innovative approach has been developed to distribute seismic loads effectively among all bridge piers without concentrating them on a few fixed-end piers.
In cases where seismic loads are considered, the traditional design featured a configuration where all horizontal loads were concentrated on a small number of fixed-end piers, which served as the central points for thermal expansion during normal temperature changes. This design aimed to prevent the transmission of significant temperature-induced loads from the bridge deck to the substructure.
However, in seismic load considerations, all horizontal loads tend to concentrate on the few fixed-end piers, creating challenges as these piers may struggle to accommodate the entire seismic load. To address this issue, an effective method has been devised that distributes seismic loads among all piers without constraining temperature loads.
For buildings, the most efficient and straightforward method for earthquake-resistant design, capable of withstanding seismic loads, is the installation of shear walls within the structure, often referred to as Reinforced Concrete Shear Walls.
The functional mechanism of shear walls lies in their effective response to horizontal loads by transforming into the shape of shear force diagrams, in contrast to the deformation pattern of moment diagrams in the frame structure. In other words, the frame structure, which undergoes significant deformation in the lower part, and the shear wall, which experiences minimal deformation in the lower part, work together as an integral system. The shear wall effectively absorbs a significant portion of the shear forces in the lower part of the building, preventing the destruction of the frame structure.
Therefore, it can be said that small apartment buildings, with walls separating individual units or small rooms, exhibit higher seismic resistance compared to larger buildings with spacious interiors, such as large auditoriums.
However, the installation of shear walls with significantly different areas on each floor or the haphazard placement of shear walls on the floor plan can lead to an imbalance in the overall rigidity of the structure. This imbalance can result in seismic damage being concentrated in the floors with weaker rigidity or lead to critical destruction due to building torsion.
Therefore, the arrangement of shear walls, forming a planar symmetry, and ensuring that the area of shear walls does not undergo abrupt changes on each floor are crucial aspects in the design of seismic-resistant structures. This planning is considered the most important issue in the design of seismic-resistant structures.
Nuclear structures are examples of structures that incorporate this concept of shear walls with numerous shear walls designed to resist seismic forces.
3.3 Seismic base isolation Structure
(1) Hiostory of Seismic base isolation Structure
Minimizing the damage caused by earthquakes has been a common concern for people living in earthquake-prone areas.
Looking into the history of seismic-resistant and base-isolation structures that gained attention after the Great Kanto Earthquake, seismic-resistant structures evolved concurrently. The modern era witnessed the recognition of reinforced concrete as superior in seismic resistance, and it became a pivotal point in the development of seismic-resistant structures following the 1906 San Francisco Earthquake (M8.3).
In Japan, two Ph.D. holders, one specializing in seismology and the other in architectural structures, conducted on-site investigations. They reported that ramen-style steel structures and reinforced concrete structures demonstrated excellent seismic performance. In 1915, they proposed the Jindo Method as a seismic design method. Subsequently, after the 1923 Great Kanto Earthquake (M7.9), the world's first seismic design regulations, incorporating a horizontal load factor of 0.1 into building codes, were established.
The concept of isolating buildings from the ground has a long history.
Professor Kellogg of the University of California claims that the world's first base-isolation structure was proposed by an English physician named Calingford in 1903. Calingford suggested a method of placing round stones under buildings and separating them from the ground.
On the other hand, Professor Henkel of the New York State University discovered that a German named Jakob proposed a method of digging holes in the ground, inserting round stones, and constructing buildings on top of them. Jakob applied for a patent for this method in the United States one month after the San Francisco earthquake in 1906.
In Japan, records of a presentation titled "Structure Receiving Seismic Vibrations," describing a method of laying logs in two directions and constructing buildings on top, were found before the Nobi Earthquake in 1891 (M8.4).
In 1921, the renowned American architect Frank Lloyd Wright designed the Imperial Hotel in Japan. While working on the project, he determined the presence of a soft layer underneath the site and suggested, "Why not float the building!" He considered the soft layer as a natural shock absorber for seismic impacts and, despite opposition, designed the structure with elevated foundations resembling floating. It is said that approximately two years after completion, the Kanto Earthquake of 1923 occurred, and the building elegantly withstood the earthquake.
Furthermore, in the United States, in 1929, Martel proposed the concept of the "Flexible First Story," which involves constructing the first floor of a building to be more flexible than the other floors to absorb seismic forces. This concept evolved through research by Green (1935) and Jacobsen (1938), incorporating the idea of energy absorption through yielding.
This concept further developed into "The Soft First Story Method" (1969, Fintel & Kahn). The initial implementation of this method was seen in the construction of the Olive View Hospital near Los Angeles. However, after its completion, the hospital suffered significant damage during the 1971 San Fernando earthquake.
Currently, it is interpreted that relying solely on the first floor, constructed with weak materials like reinforced concrete, to absorb the input energy for the entire building is considered impractical.
In Japan, the Kanto earthquake, which resulted in 140,000 casualties, served as a catalyst for the desire to "avoid earthquake damage." Following the Kanto earthquake, numerous proposals and advancements in base-isolation structures were made driven by this aspiration. In the year following the Kanto earthquake, various researchers proposed solutions such as base isolators with ball bearings, columns attached to springs, and pin-type columns with pump-type dampers (1927).
In the 1930s, there was an era known for the famous "Yukang Debate," which questioned whether a strong structure or a flexible structure was better. Among the various seismic-resistant structures proposed after the Great Kanto Earthquake, the one that was actually realized was based on the ball bearing system proposed in 1933.
The "base-isolation" proposal involved designing base-isolation columns with a large spherical bottom and connecting a spherical pin at the top. During an earthquake, the base-isolation column rotates, allowing horizontal displacement in the building, similar to the current pendulum mechanism.
This mechanism was applied to a bank building constructed in 1934, earning recognition as the world's first practical base-isolated structure.
Around the 1970s, the challenge of earthquake resistance transitioned from the research stage to practical implementation, and base-isolated structures started to be constructed worldwide.
In the aftermath of the 1963 earthquake that devastated about half of the 50,000 households in the Macedonian capital, Skopje, and caused over 80% damage when considering injuries, UNESCO coordinated international aid for recovery. With support from Switzerland, the world's first base-isolated structure using rubber bearings was completed in 1969 as a seismic mitigation measure – an elementary school.
The base-isolation device used in a 3-story reinforced concrete building consisted of 7cm-thick square rubber pads with a side length of 70cm, adhered together to form a rubber block that swells sideways under a load of about 50 tons.
(2) Seismic base isolation Building
As mentioned earlier, seismic waves exhibit strong characteristics in short-period components and weak characteristics in long-period components.
Base isolation structures, utilizing these seismic wave characteristics, aim to artificially lengthen the natural period of a structure, thereby reducing the magnitude of seismic forces acting on the structure.
In high-rise buildings, the building's natural period naturally functions as a base-isolation structure by becoming longer. However, in low-rise buildings, where the natural period cannot be easily extended structurally, a method involves inserting laminated rubber at the connection between the building and the ground to forcibly lengthen the building's natural period.
However, flexible structures, similar to a swaying reed in the wind, experience the drawback of significant displacement, even though they generate less force in terms of acceleration. To address this drawback, damping devices, known as dampers, designed to dissipate the building's vibrational energy, are sometimes installed in various forms.
The lifespan of these base isolators depends on the durability of the laminated rubber and the efficiency of the damping device. In the case of large structures, there were concerns about whether laminated rubber, a soft material, could withstand the structure's weight. This concern hindered the practical implementation of large base-isolated structures until the early 1980s.
However, with advancements in chemical engineering proving the durability of laminated rubber, recent years have witnessed the widespread adoption of base isolation, even in large structures such as museums, city halls, research facilities, etc.
In some cases, rather than implementing base isolation for the entire structure, partial base isolation, designed to protect essential equipment like large computers within a building, may be more practical. This form of base isolation is referred to as a layer isolation structure.
The difference between base-isolated structures and conventional seismic-resistant structures can be observed in the vibrational patterns illustrated in Figure-3. This difference in vibrational patterns highlights a crucial issue – the safety of interior decorations within the structure, which is considered more important than the overall structural integrity before discussing the safety of the structure itself.
Traditionally, seismic design focused on ensuring that even if partial damage occurred in the primary structural elements of a building, complete destruction would not ensue, satisfying the design conditions.
However, when examining actual seismic damage, it becomes apparent that injuries or secondary disasters resulting from the complete destruction of critical structural elements are less common compared to injuries caused by damage to interior decorations or secondary hazards such as fires due to gas pipe displacement or damage to water pipes.
Therefore, base isolation design prioritizes the safety of interior facilities and equipment over the overall structural safety. This approach is particularly emphasized for structures like museums, fire stations, government offices, hospitals, etc., where the safety of interior spaces is deemed more critical by designers.
For example, the Northridge earthquake that struck the California region on January 17, 1994, was a vertically oriented seismic event resulting in 56 fatalities and 7,300 injuries. In the affected area, there were ten hospitals, most of which suffered damage and loss of functionality. However, the USC (University of Southern California) affiliated hospital, constructed with base isolation, reported minimal damage, with no significant impact on operations.
Notably, on the morning of the earthquake, an emergency brain surgery was performed at this hospital. While surgery was temporarily halted during the seismic event, it resumed once the building's quiet shaking subsided, and the procedure was completed successfully.
(The damage was caused by the 1989 Loma Prieta earthquake and was repaired with a seismic besed isolation structure)
(3) Seismic base isolation bridge
In South Korea, although it cannot be considered as a full-fledged seismic isolation bridge, the first application of elastic bearings in bridges took place in the 1980s with material support from the IBRD (International Bank for Reconstruction and Development). Since the introduction of elastic bearings in Japan during that period, domestic applications began by imitating the shape of these bearings.
However, in the early stages, due to the lack of established rubber quality, incidents occurred where the rubber and steel plates were delaminated under the vertical load caused by the bridge's self-weight. This led to a controversy resulting in the removal of all installed elastic bearings. Consequently, for some time, domestic civil engineers harbored distrust towards rubber products.
In 1987, with the establishment of the Korean Standard Specification (KS F4420) for elastic bearings, ensuring the quality of rubber products, the use of elastic bearings in domestic bridges gained momentum. Initially, these early elastic bearings were employed not so much for their role in creating longer natural frequencies for seismic isolation but rather for absorbing vehicular impact loads and providing noise reduction, owing to the favorable properties of rubber materials. Presently, numerous bridges in South Korea are constructed using elastic bearings.
In recent times, elastic bearings have gained preference, particularly in railway bridges, due to their superior everyday usability in terms of noise reduction and impact resistance compared to steel bearings.
In South Korea, the application of seismic isolation bridges, specifically those with elongated natural frequencies and vibration energy absorption effects, began in earnest around 1997.
The increased interest in seismic isolation bridges domestically was triggered by the growing prevalence of such bridges in the United States and Japan. One of the motivations for exploring seismic isolation bridges in South Korea was to address the drawback of traditional steel bearings, where seismic loads concentrate at the fixed supports, making it challenging to design continuous bridges with multiple spans due to difficulties in managing horizontal forces. The attempt was made to leverage the load distribution effect of seismic isolation bearings.
Advantages of treating bridges as continuous structures, as opposed to simple bridges, include reduced expansion joint devices, leading to improved vehicle drivability. Additionally, there are benefits in terms of maintenance and ease of addressing issues such as waterproofing and noise in the expansion joint areas.
The first seismic isolation bridge with lead rubber bearings applied in South Korea was the Warren truss section of Gwangandaegyo Bridge, Section 3, located in Gwang-an-dong, Busan. The Section 3 of Gwangandaegyo Bridge transitioned into a seismic isolation bridge during the construction phase due to design changes and was pursued as a seismic isolation bridge from the design stage. Another example of a bridge constructed with seismic isolation principles from the design stage is the replacement project for Dangsan Railroad Bridge.
The Dangsan Railroad Bridge, being a railroad bridge with the characteristic requirement of no deformation in the direction of the rail, applied seismic isolation concepts in the direction perpendicular to the track, while adopting seismic isolation concepts in the longitudinal direction.
Furthermore, the introduction of seismic isolation bridges gained momentum with the construction of the front elevated bridge at Incheon International Airport's passenger terminal. This marked the beginning of seismic isolation bridges in South Korea. Presently, these bridges have become so widespread that for long-span bridges, it is almost impossible to design them without employing seismic isolation bearings. In recent times, the performance of such bridge structures has transitioned from the realm of seismic systems to the architecture market, emphasizing the importance of digital data storage in the information age. The use cases and achievements in these bridge structures are now extending beyond the seismic system's origins, highlighting the shift towards digital data preservation in the architecture sector.
4. Closing Remarks
We have become acutely aware of human vulnerability to the forces of nature through the damages caused by the 1995 Great Hanshin Earthquake in Japan. There is a growing interest in whether a similar earthquake could occur on the Korean Peninsula, given its proximity to Japan. If such an earthquake were to occur, there is a concentrated effort among the Korean population to understand how to cope with it.
While predicting earthquakes remains impossible even with modern science, devising strategies to deal with them is well within human capability. Therefore, it is essential to assume the possibility of earthquakes in the Korean Peninsula, traditionally considered a seismic safe zone, and establish contingency plans for how we should respond in the event of an earthquake.
Despite heightened awareness and scrutiny regarding the seismic safety of large structures such as high-rise buildings and nuclear power plants due to recent economic development, we tend to overlook the safety of everyday architectural and civil engineering structures in which we live.
Let's imagine a scenario where a magnitude 6 or 7 earthquake occurs in the fault of Yangsan, which is considered to have the highest seismic risk in our country. First, we may be concerned about the safety of the Gori Nuclear Power Plant located in the nearest area to the epicenter.
Although the safety of the nuclear power plant could be questionable depending on the magnitude of the earthquake, what about other residential areas and urban centers in the Busan region? According to common knowledge, in the event of a seismic event of such magnitude, more than half of the buildings in the nearby city would be severely damaged or collapsed, bridges would be destroyed, and dams would face potential collapse.
Under the rubble of collapsed buildings, there would be cries of anguish from trapped victims, and inside damaged structures, there would be pleas for help from injured individuals trapped under large furniture or household items. Along the roadsides, there would be casualties from falling exterior tiles or glass fragments from nearby high-rise buildings, and citizens unable to evacuate due to jammed entrances, facing hazards such as fires and casualties.
Even for those fortunate enough to survive the earthquake, they would likely be busy rescuing injured victims or verifying the survival of their loved ones. Additionally, with transportation routes like bridges severed, it would take days for relief supplies to reach affected areas. The aftermath would be chaotic, with people scrambling for necessities such as water, emergency rations, and medication.
This imaginary scenario is not just a product of the author's imagination but reflects real-life events that have occurred in various regions around the world.
To prevent such a horrific situation from becoming a reality, we need to address various aspects step by step.
Firstly, we should start by improving the housing structures of vulnerable groups, such as brick buildings.
Brick structures offer no resistance against horizontal loads like seismic forces, resulting in instantaneous brittle failure. The major drawback of brittle failure is that it occurs without any warning sounds, leaving no temporal margin for evacuation.
Secondly, the task involves securing easily collapsible large furniture inside buildings by affixing them to the walls. The focus is on mitigating injuries caused by furniture displacement inside buildings, which tends to be more numerous than casualties resulting from building collapses. This is a feasible action with minimal economic burden.
Thirdly, simultaneous with an earthquake, it is essential to lock kitchen gas valves and, in the case of apartments, leave entryways open.
Fourthly, at the national level, efforts should be directed toward securing refuge spaces, such as parks, within urban areas.
Investing significant funds to reinforce structures is an integral part of seismic design, with the preference for robust materials like reinforced concrete over blocks. Additionally, widespread adoption of base-isolation design is believed to play a crucial role in disaster preparedness.
Topic
Seismic Design
Seismic Isolation Design
Vibration Control Design
Period Characteristics
Resonance Phenomenon
Response Spectrum
Vibration Control Structure
Earthquake-resistant Structure
Seismic Isolation Structure
History of Seismic Isolation Structures
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Dr. Gyusik Jeon, with over 20 years of experience in Architectural Engineering, has a diverse career including roles at KEPCO's Power Research Institute (1980-1997), Technical Director at Unison Construction (1997-2000), and currently works with a seismic base isolators production company. He graduated from Busan National University in Civil Engineering and holds a Master's and Ph.D. from the University of Tokyo's Seismic Research Institute.
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