Advanced Techniques, Benefits and Challenges of Retrofitting the Existing RC Buildings
Any technology or material has its limitations and to meet the new requirements, new technologies have been invented and used over the ages. A large number of reinforced concrete structures located at seismic prone areas are not capable of withstanding earthquakes according to the current coal provisions. Furthermore the seismic behavior of the existing buildings are affected due to design deficiency, construction deficiency, additional loads, additional performance demand, etc. Recent earthquakes have clearly demonstrated an urgent need to upgrade and strengthen these seismically deficient structures. The retrofitting is one of the best options to make an existing inadequate building safe against future probable earthquake or other environmental forces. Retrofitting reduces the vulnerability of damage of an existing structure during a near future seismic activity. It aims to strengthen a structure to satisfy the requirements of the current codes for seismic design. A significant amount of research work has been carried out in recent years to develop various strengthening and rehabilitation techniques to improve the seismic performance of structures. This paper aims to present an overview on different innovative and cost effective techniques of retrofitting for strengthening the damaged structure.
Earthquakes of varying magnitude have occurred in the recent past across the globe, causing extensive damage to life and property. The recent earthquake (Bandi Mir Samdani neighbourhood of Muzaffarabad, Pakistan) that struck on 8th Octobar,2008 destroyed many houses, schools, hospitals etc. Those buildings which were partly or totally destroyed have naturally to be rebuilt, and for safety in future, must be constructed using adequate earthquake resisting measures according to the various Pakistani standards and appropriate guidelines UBC 1997.
The seismic behaviour of the existing buildings is generally affected by their original structural inadequacies, material degradation due to aging and alterations carried out during use over time. These kind of structures cannot survive against severe earthquake. The large strain energy released during an earthquake travel as seismic waves in all directions. These waves can be classified as body waves consisting of P-waves (Primary) & S-waves (Secondary) and surface waves consisting of L-waves & Rayleigh waves. S-waves cause maximum damage to the structures by vibrating the surface in horizontal and vertical direction The main types of damage in reinforced concrete structures due to earthquake are cracking in tension zone, diagonal cracking in the core and loss of concrete cover, stirrups bursting outside and buckling of main reinforcement. The complete replacement of such buildings in a given area is just not possible due to a number of social, cultural and financial problems. Therefore, seismic strengthening of existing undamaged or damaged buildings is a definite requirement. It will involve actions for upgrading the seismic resistance of an existing building so that it becomes safer under the occurrence of probable future earthquakes.
The main objective of this paper is to describe the all techniques to give a clear understanding to the readers about repair and retrofitting of RC structures. Such as reinforced concrete jacketing, steel jacketing, fiber reinforced polymer, composite jacketing, steel bracing system, addition of shear walls, seismic isolation system.
SIX MAJOR REASONS TO SEISMIC RETROFIT
1. Marketability of a building is improved
Buyers are attracted the security a seismic retrofit provides to tenants. The number of potential lenders increases when the Probable Maximum Loss (PML) is low. More lenders can mean more buyers!
2. The risk of injury and legal litigation is reduced
Owners can lose substantial amounts of money if it can be proven they were aware a building needed structural work, but had no plan in place to correct the problem. No amount of insurance coverage will probably cover successful litigation against negligence. A thorough seismic retrofit provides peace of mind and asset protection.
3. Earthquake coverage can be reduced
A lower coverage cap can reduce premiums. (At this time, some insurance companies do not recognize the PML of a building).
4. Lenders who request a PML of less than 20% are usually satisfied when a thorough and professional seismic retrofit has been completed.
5. Insurance companies in the future may not write coverage for earthquakes due to past losses and other events. Rates have increased 3 to 6 times the rate charged since 2005!
6. Tenants who consider the operation of the building critical to the survivability of their businesses feel more secure and will remain in occupancy contracts for longer periods.
THE BENEFITS AND CHALLENGES OF RETROFITTING
The benefit:
? Retrofitted buildings are more adaptable and suitable to existing activities or future activities if required, more comfort;
? Retrofitted buildings are more energy efficient, lower carbon emissions from the building operations;
? Greater sustainable use of embodied-carbon investment (capital carbon).
The challenges of retrofitting:
? Expensive and inconvenient;
? Internal spaces may reduce upon installation of internal wall-insulation;
? Might cause negative impact to heritage and archaeological assets caused by usage of unproven methods, technologies or instruments;
? Further research is needed especially on insulation mechanism on walls and the effect on retrofit on buildings fabrics;
? More education, training and activities on maintaining and preserving the buildings need to be taught to address issues and to create awareness;
? The risk of retrofitting needs to be highlighted, not just focusing on the benefits of retrofitting and discussion between retrofit and refurbishment.
Other benefits of retrofit existing buildings includes; cost saving in long run by reducing the usage of energy and water by incorporating new technology, services or equipment; increasing the comfort level in a building by redesign the facade and interior to improve end users productivity and satisfaction through improving interior thermal comfort; lowering the greenhouse emission and optimizing the water usage in building; future-proof buildings which means the building will be use and last for many years when it is equipped with current technology based; and preserving cultural and heritage significance of an existing buildings by enhancing the building exterior and interiors to meet current standards and design based on the needs of end users.
CONCLUSION
Seismic retrofitting has now become a crucial issue. Recent occurrences of earthquakes in different parts of the world have clearly demonstrated the urgency of repairing seismic deficient structures. Several numbers of experimental and analytical programs focused on innovative seismic retrofitting techniques have been included in current state of an art review. Design guidelines and recommendations should be made more readily available to ensure more rapid and effective applications of various strengthening methods. Design manuals and codes of practice should be updated to take these issues into consideration. However, before applying any seismic retrofit method to a damaged or deficient structure, a proper and accurate assessment of the seismic performance and current state of the structure is essential.