Seismic Retrofitting of Tall Buildings And Skyscrapers
A skyscraper is a tall, continuously livable structure with multiple stories. The phrase was first used to refer to a structure with at least 35 to 50 stories, typically used for commercial, industrial, and residential uses. A tall structure is also referred to as a skyscraper.
Skyscraper design and construction require making livable, safe places in extremely tall structures. The structures must bear their weight and withstand wind and earthquakes, as well as defend residents from fire. However, they must also be easily accessible, even on higher floors, and must offer the residents with utilities and a comfortable environment. Given the delicate balances between engineering, economics, and construction management, skyscraper design issues are among the most challenging.
Seismic Retrofitting
Retrofitting is the process of integrating new features or technologies into existing systems in order to increase the stability of the building. It involves making modifications to an existing structure in order to safeguard it against flooding and other dangers like strong winds and earthquakes.
Seismic retrofitting refers to the alteration of current structures to increase their resistance to seismic activity, ground motion, or soil failure as a result of earthquakes. Seismic retrofitting is clearly necessary, as evidenced by our growing understanding of the seismic demand on structures and by the recent occurrence of significant earthquakes close to urban areas.
Seismic retrofitting is an advancement in building technology that addresses the effects of natural catastrophes on structures and their increasing frequency and intensity.
Need for Seismic Retrofitting of Tall Buildings And Skyscrapers
To protect the security and safety of a facility, its occupants, the machinery, equipment, and supplies.
Necessary to lower the risk and losses caused by non-structural factors.
Primarily focused on structural upgrades to lower seismic risk.
Hospitals are an example of a building that has to be strengthened since its services are seen to be crucial immediately following an earthquake.
Seismic Retrofitting Strategies For Tall Buildings And Skyscrapers
Following the introduction of new seismic regulations and the accessibility of modern materials (such as fiber-reinforced polymers (FRP), fiber reinforced concrete, and high strength steel), seismic retrofitting (or rehabilitation) solutions have been developed over the past few decades.
The use of base isolation technologies and/or additional damping to reduce the seismic demand.
Enhancing the local carrying capacity of structural components. This approach takes a more cost-effective approach to upgrading local capacity (deformation/ductility, strength, or stiffness) of specific structural components because it recognizes the inherent capacity within the current structures.
Retrofitting with selective weakening. This is a counterintuitive approach to changing the structure’s inelastic mechanism while maintaining its intrinsic capacity.
Having movable connections, to allow for more movement between seismically independent structures.
Adding seismic friction dampers to add dampening and a configurable amount of extra stiffness at the same time.
More comprehensive methods of building retrofitting, such as combined seismic and energy retrofitting are also being investigated, and more research is being done in these areas. By combining seismic strengthening with energy retrofitting, these integrated techniques will optimize cost reduction while enhancing the seismic and thermal performance of structures.
Seismic Retrofitting Techniques for Tall Buildings And Skyscrapers
Buildings made of concrete that are susceptible to earthquake-related damage and failure must use seismic retrofitting techniques. Every year for the past 30 years, there have been earthquakes of moderate to severe intensity. These occurrences cause failures and damage to concrete structures.
Thus, the goal is to concentrate on a few particular procedures that could advance practice for the assessment of the seismic vulnerability of important existing reinforced concrete structures and for their seismic retrofitting using various cutting-edge techniques like base isolation and mass reduction. Some of the most widely used retrofitting techniques are:
Adding New Shear Walls
This method is frequently used to update tall buildings with non-ductile reinforced concrete frames. Precast or cast-in-place concrete components may be used as the additional pieces.
Shear walls are commonly used for seismic retrofitting of existing structures. These walls are designed to resist lateral forces, such as those generated by earthquakes, by transferring the loads to the foundation. They are typically made of reinforced concrete, masonry, or wood and are strategically placed throughout the building to provide stability and reduce the potential for collapse during a seismic event. Shear walls can be added to existing structures by attaching them to the building frame or by constructing them as freestanding elements within the building. The use of shear walls for seismic retrofitting is an effective and widely used approach to enhance the safety and resilience of structures in earthquake-prone regions.
2. Integrating Steel Bracing
Steel bracing is a common method used for seismic retrofitting of existing structures to improve their ability to withstand earthquakes. Bracing involves the installation of steel members in a diagonal pattern to transfer the seismic forces acting on the structure to its foundation. The bracing system provides additional support and stiffness to the structure, reducing its susceptibility to damage during a seismic event. Steel is a popular material for bracing because of its high strength, ductility, and durability, which allows it to withstand significant seismic forces. Proper design and installation of steel bracing can significantly improve the seismic performance of a building and help ensure the safety of its occupants.
Jacketing
Jacketing is a popular technique for seismic retrofitting of existing buildings. In this technique, a new layer of reinforced concrete is added to the existing structure, which increases its strength and stiffness. The new layer also provides additional protection against earthquake-induced damage. Jacketing is particularly useful for buildings that were constructed before the development of modern seismic design codes and standards. The technique can be applied to a variety of building types, including concrete, masonry, and steel buildings. The effectiveness of jacketing depends on several factors, such as the quality of the existing structure, the design of the new layer, and the quality of construction.
Base Isolation
Base isolation describes the separation of the superstructure from the ground. It is the most effective tool for controlling passive structural vibration. Base Isolation is also known as Seismic Isolation.
Base isolation ensures that the structural components of the superstructure significantly dissociates from the ground's trembling, preserving the integrity of the building and improving its seismic performance. Both freshly constructed buildings and seismic upgrades of existing structures can use this earthquake engineering method, which is a type of seismic vibration control.
The process of retrofitting a building with base isolators typically involves the following steps: First, the building is evaluated to determine the type and amount of base isolators required. Then, the building's foundation is reinforced to ensure that it can support the additional weight of the isolators. Next, the isolators are installed between the building's foundation and its superstructure, using a combination of grout, anchor bolts, and steel plates to ensure a secure connection. Finally, the building is reconnected to the utilities and the surrounding infrastructure, and any necessary modifications are made to the interior and exterior finishes. The result is a building that is better able to withstand the forces of earthquakes and other seismic events..
Advantages of Base IsolationBuilding motion is separated from the ground. Lower seismic loads mean less structural damage, Minimal superstructure repair.
The structure can continue to be used while being constructed.
Does not require a significant alteration to the existing superstructure
Disadvantages of Base IsolationIt is expensive.
Unlike other retrofitting methods, it cannot be used on partial structures.
Implementation is difficult and inefficient.
Mass Reduction Technique
The mass reduction technique is a highly effective method for seismic retrofitting. By reducing the mass of a structure, the force generated by an earthquake can be significantly decreased. This can greatly increase the structure's resistance to seismic activity and reduce the risk of structural damage or collapse. Additionally, mass reduction can often be achieved through relatively simple means, such as removing non-essential elements or replacing heavy materials with lighter ones. Overall, the mass reduction technique is an important tool for ensuring the safety and resilience of structures in earthquake-prone areas.
Supplementary Dampers
Supplementary dampers are a commonly used strategy for seismic retrofitting, which involves modifying existing buildings to better withstand earthquake shaking. These dampers work by dissipating energy during seismic events, reducing the overall force experienced by the building. They are typically installed at the building's base or within the structure, and can be either passive or active systems. Passive dampers, such as friction or viscous dampers, rely on the physical properties of the materials to absorb energy. Active dampers, on the other hand, use sensors and control systems to adjust their damping properties in real-time, providing more precise control over the building's response to seismic events. Overall, the use of supplementary dampers can be an effective way to enhance the seismic performance of existing structures, improving their safety and resilience in the face of earthquakes.
Tuned Mass Dampers
Tuned mass dampers (TMD) are spring-based devices that use movable weights. These are frequently used in extremely tall, light constructions to lessen wind sway. In eight to ten storey buildings that are vulnerable to damaging earthquake induced resonances, similar designs may be used to impart earthquake resistance.
Slosh Tank
Slosh tanks, also known as tuned liquid dampers, are a form of seismic retrofitting that can be used to mitigate the effects of earthquakes on structures. These tanks consist of a liquid-filled container that is designed to move in response to the shaking caused by an earthquake. As the liquid in the tank sloshes back and forth, it absorbs the energy of the seismic waves, reducing the force and displacement that is transmitted to the building. Slosh tanks can be particularly effective for tall buildings that are vulnerable to the lateral forces generated by earthquakes. However, they do require careful design and installation to ensure that they function correctly, and they may not be suitable for all types of structures. Overall, slosh tanks can be a useful tool for enhancing the seismic resilience of buildings in earthquake-prone areas.
Seismic retrofitting is an important process that can help to keep buildings and other structures safe during an earthquake. If you’re looking to retrofit your building or structure, contact us for your seismic retrofitting plans www.jpcdesignconsortium.com/contact-us.