SEISMIC ISOLATION
Seismic isolation (earthquake isolation or base isolation) is a method that protects the structure and all the components inside the building from the destructive effects of the earthquake by creating a layer between the building and the ground thanks to special devices (earthquake isolation devices) placed between the building itself and its foundation.
Seismic Isolation and Working Principle
Seismic isolation (earthquake isolation or base isolation) is a special device (earthquake isolation devices) placed between the building itself and its foundation, creating a layer between the building and the ground, and the aim is protecting all components inside the building from the destructive effects of the earthquake.
Earthquake isolators (seismic isolators or base isolation devices) are placed one per column in buildings and more than one under the curtain, and the superstructure is separated from the foundation and the ground.
Seismic isolation increases the period of the structure to which it is applied, thanks to the lateral flexibility of the devices, and meets the horizontal displacement demand that will occur during an earthquake at the isolator interface (with earthquake isolation devices). In addition, the damping rate, which is accepted as 5% in normal structures, increases to 20% and above when it comes to earthquake insulation, and plays an extra role in reducing the destructive effects of the earthquake.
Earthquake isolation protects both the structural and non-structural elements of the superstructure and thus ensures that the building survives any earthquake with zero damage and remains fully functional.
Earthquake isolation is the only proven and applicable method that can control relative floor drifts and floor accelerations in a building at the same time. In addition, earthquake insulation is the only method that enables the structure and all its components (structural and non-structural elements) to survive the largest expected earthquake in the area where that structure is located, and thus guarantees the uninterrupted use of the building after an earthquake.
All national and international earthquake regulations are prepared with the acceptance that the structure will be damaged at a certain level depending on the ductility level, otherwise it is not possible to design the structures. That is, all structures will receive a certain level of damage under the expected design earthquake in that area. The purpose of the regulations is not to provide damage, but to ensure the safety of life by preventing the collapse of the structures. Damage to the buildings in any earthquake can only be achieved with earthquake insulation application. Even if the loss of life can be minimized when buildings are constructed in accordance with the regulations, the only method that can prevent financial losses that will occur after a major earthquake is earthquake insulation. However, as it will enable non-structural elements (walls, ceilings, mechanical-electrical parts, cabinets, etc.) to survive a major earthquake without damage, earthquake insulation has a great psychological benefit as well as economic benefits on human health.
In addition, with the widespread use of earthquake insulation, the damage to the environment during the repair and demolition works of the buildings damaged after the earthquake is also prevented.
Detailed analysis of the above mentioned subject is available in the file named “Basic Differences in Classical and Earthquake-Proof Design in Buildings”. You can reach this file from here.
The visual regarding the above mentioned subject is available in the file named “Earthquake Resistant Design Options”. You can reach this file from here.
Important Points To Be Considered with Sismic Izolation
Important issues to be considered in a building with earthquake isolation are listed below.
Electrical and Mechanical Details
In addition to the isolator, since the structure is completely separated from the ground, the mechanical details (all connections such as electricity-water-waste-natural gas) must also be supported with special details in accordance with earthquake isolation and movement in all directions. Such special applications may be commercially available.
Photos of Example connection details will be added here.
Joint Details
The earthquake insulated building will be completely separated from the ground and a gap will remain around the building, since it is built in such a way that it can move freely in all directions during a possible earthquake. This gap must be crossed with all-round joints. Again, standard joints produced for such applications can be found in the market.
Drawings and photos of sample joint details will be attached here.
Vertical Component of the Earthquake
None of the earthquake isolation devices alone have an effect against the vertical component of the earthquake. If extra precautions are to be taken against vertical earthquakes, it is mandatory to use extra special damping systems in addition to the earthquake isolator. On the other hand, the effects of vertical components of earthquakes on both structural and non-structural elements are much lower than horizontal components. Considering this, according to the results of the structural analysis, it is decided whether or not to take measures against vertical earthquakes and as a result, extra special devices are used if necessary.
Building Architecture
In buildings that are planned to be built with earthquake isolators, the building must be designed and modeled with isolator starting from the architecture. For example, the dimensions of the columns where insulators will be placed should be adjusted by calculations and the general architecture should be determined in a way that is suitable for the insulator application. The architectural approach and design in buildings with and without insulators are different from each other, and an insulator cannot be applied to an architecture that is planned and prepared without an insulator. For this reason, a building for which an earthquake isolator is planned should be solved with an appropriate architecture from the beginning.
The basic points to be considered in terms of architecture in earthquake insulated buildings are available in the file named “Architecture in Earthquake Insulated Buildings – General Approach Principles”.
Static Calculations
After the architectural solutions of the building are adjusted to be compatible with the earthquake isolator application, static calculations can be made more effectively. Similarly, static calculations should be made with structural analysis programs that have earthquake isolator models, the capacity to perform linear and nonlinear analyzes and have proven themselves in this field.
Before static calculations begin, published by AFAD be taken from Turkey Earthquake Hazard Map design spectrum together with site-specific seismic hazard analysis also be outsourced to experts and concerned the structure of the accounts should be started thereafter.
The basic points to be considered during static modeling and analysis in earthquake insulated buildings are available in the file named “Static Modeling in Earthquake Insulated Buildings – General Approach Principles”.
Design Oversight System
Earthquake-proof structures fall under the category of “special building”. In this context, T.C. The Ministry of Environment and Urbanization requires working with predetermined experts during the design and implementation stages of special buildings. According to this system called “Design Supervision (TGUA in Turkish)”, when it comes to an earthquake insulated building, it is mandatory to work with design supervisors at both the site-specific earthquake hazard analysis (TGUA-1) and the design of the earthquake insulated structure (TGUA-5). Design supervisors are responsible for checking and approving the calculations made in the relevant areas.
Design Supervisor for detailed information about the system, enacted on Official Gazette dated 11.01.2019 “Turkey Earthquake Building Regulation Communiqué Regarding the Scope of Things Design Surveillance and Control Service” is found in the document says.
Field Installation:
It is very important that the insulators are installed in the relevant places in the field by the expert teams in this field. The assembly of these devices should be done very precisely and carefully. Otherwise, no matter how correct design and production is made, it is very difficult to return an error that will occur during assembly.
Field assembly application examples will be added here.
Structural Differences and Savings
When earthquake isolation is applied to a building, it cannot be expected that a size or reinforcement savings will be achieved in structural elements. In some cases, savings such as reducing the size of the superstructure elements and the amount of reinforcement may be in question, but this may vary for each structure and must be checked with calculations.
In buildings with earthquake isolation, the need for shear walls is reduced or completely eliminated.
Square columns and beam frames should be preferred instead of thin and long column / shear wall type carrier systems and floor without beams in seismically isolated structures.
Reinforcement with Earthquake Isolation
Earthquake isolation can be used not only in new constructions but also on existing structures. However, beforehand, an expert team must make an assessment in order to understand whether the building is suitable for strengthening with earthquake isolation. After the preliminary checks by the expert team, if there is no obstacle in reinforcement with isolator; It starts with determining the concrete quality of the existing structure (with current core purchases and material tests) and understanding the structural system of the building. Then, the building is modeled with an earthquake isolator and analyzed. Meanwhile, the strength and dimension checks of the structural elements on the floor and ceiling of the floor where the isolator will be applied and the columns are also checked and the strengthening requirement in the structural elements is determined. As a result of these operations, the scope of the construction works to be carried out during the reinforcement of the building with isolator is also determined. Most of the procedures written above are the work that should be done when a retrofit without an isolator is already planned. Regardless of isolator production and assembly, with the determination of the construction works to be carried out, whether the isolator can be reinforced and the final costs of the work are revealed.