Development of Anti-earthquake Structures: Seismic Retrofit
Moving plates and volcanism as well as interactions among the hydrosphere, biosphere, atmosphere, and solid Earth are all manifestations of Earth's dynamic nature. Earthquakes are also indication that Earth is an internally active planet. As one of nature's most frightening and destructive phenomena, earthquakes have always aroused a sense of fear and have been the subject of myths and legends.
geologists define earthquake as the shaking or trembling caused by the sudden release of energy, usually as a result of faulting, which involves displacement of rocks. After an earthquake, continuing adjustments along a fault may generate a series of earthquakes known as aftershocks. Most of these are smaller than the main shock, but they can cause considerable damage to already weakened structures.
through the years, scientists around the world has never been invented a machine that could ever predict when and where this earthquake strikes. Thus, this can't be avoided, but this stagnant issue triggers the engineers to innovate design that could oppose this phenomenal disturbance and give surge of this seismic retrofit.
The study answers the questions:
1. What is Seismic Retrofit?
2. What are the advantages of the anti-earthquake structures?
3. what are the possible problems that may occur and its solutions?
Seismic Retrofit
Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. with better understanding of seismic demand on structure and with our recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged.
The retrofit techniques outlined here are also applicable for other natural hazards such as tropical cyclones, tornadoes, and severe winds from thunderstorms. Whilst current practice of seismic retrofitting is predominantly concerned with structural improvements to reduce the seismic hazard using the structures, it is similarly essential to reduce the hazards and losses from non-structural elements. It is also important to keep in mind that there is no such thing as an earthquake-proof structure, although seismic performance can be greatly enhanced through proper initial design or subsequent modifications.
A seismic retrofit not only protects the employees, customers, equipment and inventory inside a building, but can lower insurance premiums, attract lenders and help guarantee the building's status as an essential facility, providing peace of mind and longevity for renters.
The cost of hardware installed during the seismic retrofit generally becomes equity in the building because it increases the property's value lowers its Probable Maximum Loss (PML). A PML of less than 20% can reduce insurance premiums. Most building owners can recover their seismic retrofit costs in 2-8 years because of reduced earthquake insurance premiums.
The lower PML a seismic retrofit may provide can also be important when the times comes to sell or add improvements to the building. A PML of less than 20 % fulfills the requirements of most lenders and because more lenders will be able to lend on your property, you'll attract more qualified buyers or be able to more easily acquire cash for improvements.
Advantages
Perhaps the most practical benefit from a seismic retrofit is very simply, the prevention of loss. The losses incurred from a fifteen-second earthquake can be devastating both to the building as wells as the people inside it. Many permanently because of the destruction caused by seismic activity. Lost profit because of an earthquake is often related to:
- Loss of life
- Medical cost
- Loss of tenants
- Litigation from employees& tenants
- Cost of temporary relocation
- Loss of assets within the building
- Loss of building productivity, building use and overall business operations
A seismic retrofit will eliminate or minimize these losses, ultimately benefiting the building's owner.
Seismic retrofit is primarily applied to achieve life safety; options for the level of seismic retrofit generally fall into four classifications, depending on the expected seismic activity and the desired level of performance. Realistically, for historic buildings, only the first three categories apply.
Basic Life Safety. This addresses the most serious life-safety concerns by correcting those deficiencies that could lead to serious human injury or total building collapse.Upgrades may include bracing and tying the most vulnerable elements of the building, such as parapets, chimneys, and projecting ornamentation or reinforcing routes of exit. It is expected that if an earthquake were to occur, the building would not collapse but would be seriously damaged requiring major repairs.
Enhanced Life Safety. In this approach, the building is upgraded using a flexible approach to the building codes for moderate earthquakes. Inherent deficiencies found in older buildings, such as poor floor to wall framing connections and unbraced masonry walls would be corrected. After a design level earthquake, some structural damage is anticipated, such as masonry cracking, and the building would be temporarily unusable.
Enhance Damage Control. Historic buildings are substantially rehabilitated to meet, to the extent possible, the proscribed building code provision. Some minor repairable damage would be expected after a major earthquake.
Immediate Occupancy. This approach is intended for designated hospitals and emergency preparedness centers remaining open and operational after a major earthquake.Even most modern buildings do not meet this level of construction, and so for a historic building to meet this requirement, it would have to be almost totally reconstructed of new materials which, philosophically, do not reflect preservation criteria.
Problems
Seismic retrofit is expensive and needs much budget. To avoid another retrofitting, an owner must make sure that the contractor he/she must hire is expert enough to assure the project's durability.
Seismic Retrofitting is a suitable technology for protection of a variety of structures. It has matured in the recent years to a highly reliable technology. But, the expertise needed is not available in the basic level. The main challenge is to achieve a desired performance level at a minimum cost, which can be achieved through a detailed nonlinear analysis. Optimization techniques are needed to know the most efficient retrofit for a particular structure. Proper Design Codes are needed to be published as code of practice for professionals related to this field.
Enhanced Life Safety. In this approach, the building is upgraded using a flexible approach to the building codes for moderate earthquakes. Inherent deficiencies found in older buildings, such as poor floor to wall framing connections and unbraced masonry walls would be corrected. After a design level earthquake, some structural damage is anticipated, such as masonry cracking, and the building would be temporarily unusable.
Enhance Damage Control. Historic buildings are substantially rehabilitated to meet, to the extent possible, the proscribed building code provision. Some minor repairable damage would be expected after a major earthquake.
Immediate Occupancy. This approach is intended for designated hospitals and emergency preparedness centers remaining open and operational after a major earthquake.Even most modern buildings do not meet this level of construction, and so for a historic building to meet this requirement, it would have to be almost totally reconstructed of new materials which, philosophically, do not reflect preservation criteria.
Problems
Seismic retrofit is expensive and needs much budget. To avoid another retrofitting, an owner must make sure that the contractor he/she must hire is expert enough to assure the project's durability.
Seismic Retrofitting is a suitable technology for protection of a variety of structures. It has matured in the recent years to a highly reliable technology. But, the expertise needed is not available in the basic level. The main challenge is to achieve a desired performance level at a minimum cost, which can be achieved through a detailed nonlinear analysis. Optimization techniques are needed to know the most efficient retrofit for a particular structure. Proper Design Codes are needed to be published as code of practice for professionals related to this field.
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