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Wednesday, January 11, 2017

BASE ISOLATION AND SEISMIC CONSIDERATION IN EARTHQUAKE RESISTANT STRUCTURES - 4

Page 4                                                                                                                            
CHAPTER 6
CASE STUDY

It has become evident in recent times that base isolation can be very effective in the event of an earthquake. The cost of installing base isolation systems has been so great that it is generally only used for emergency centres, historical buildings, and buildings housing very expensive and sensitive equipment and are limited to developed nations only and in a developing country like India, base isolation technique is as good as nonexistent. Having technological &research institutes in almost every part of a country, still research in this field is limited to few IITs only. The only instance of base isolation in India is at district hospital constructed post 2001 Bhuj earthquake incorporating lead rubber bearing system Cost involved in constructing a new building is higher than the cost of conventional earthquake resistant structural system. Seismic isolation bearings are expensive. Due to these economic considerations, even in developed countries these devices have so far been used for important buildings only. To enable its use for common buildings, some low cost devices have to be developed.


Fig. 6.1.Time Period of base isolated & non base isolated on soft & stiff soil.
(Source: S. J. Patil, G. R. Reddy Website: www.ijetae.com)

Soft soil ground condition isn’t suitable for base-isolated structures. After LRB yield, the structure period corresponding to the equivalent linear stiffness can be further prolonged. As a result, the natural period just enters into the range of the predominant period of earthquake wave. It leads to the acceleration amplification which makes the enlargement of seismic energy response. Consequently, it should be paid much attention on the design of absorption and isolation for base-isolated structures under the soft soil ground condition.
Requirement of tests on prototype bearing of every type increases the cost of the project. Therefore, development and standardization of testing methods for evaluating the properties of isolation devices should be formulated.


Fig. 6.2. Rubber bearing provided to Bhuj hospital.
(Source: S. J. Patil, G. R. Reddy Website: www.ijetae.com)

Fig. 6.3. Indian scenario for base isolation
(Source: S. J. Patil, G. R. Reddy Website: www.ijetae.com)

But however some low cost isolation devices can be incorporated to ordinary structures situated in high seismic zones, especially to structures from rural regions where maximum part of a India’s population dwells. Of course, these low cost isolation devices, can never met the performance level as those of high end devices like LBR, FPS etc but can be of great help in minimizing number of casualties during major seismic events.
Some examples of low cost isolation system include rubber bearings reinforced with fibre glass mesh instead of steel(this reduces weight as well as cost of the bearings to great extend.

 
Fig. 6.4. Scrap tyre pad as low cost isolator device
(Source: Pallavi WamanraoTaywade, Madhuri Narayan Savale)

Scrap rubber tyre pads can also be utilized for isolating a building. Since the tires are being designed for friction, load transfer between scrap tire layers would be large enough to keep all layers intact. A minimal slip generated between the piled layers at high strain rates may even help to dissipate some extra energy. Steel mesh in tyre can be assumed to provide vertical rigidity to an extent. Rectangular shaped layers cut from tread sections of used tires and then piled on top of each other to form Scrap Tire Pad (STP) can function as an elastomeric pad.


CHAPTER 7
CONCLUSION

Seismic base isolation method has proved to be a reliable method of earthquake resistant Design. The success of this method is largely attributed to the development of isolation devices and proper planning. Different types of isolation devices have been proposed and extensive research has been made on them.
They can serve the purpose for almost all types of conditions. Adaptable isolation systems are required to be effective during a wide range of seismic events. Besides, the existing devices are expensive and to make isolation feasible for ordinary buildings, it is efforts are required to develop cost effective devices.

REFERENCES

[1]. Pallavi Wamanrao Taywade, Madhuri Narayan Savale.“International Journal of Innovative Research in Science, Engineering and Technology ”(An ISO 3297: 2007 Certified Organization) Vol. 4, Issue 3, March 2015, pp 1215-1228
[2]. S. J. Patil, G.R.Reddy.“International Journal of Emerging Technology and Advanced Engineering” Website: www.ijetae.com (ISSN 2250-2459), Volume 2, Issue 7, July 2012, pp438-453
[3]. J. Appl. “Sci. Environ. Manage. ” Vol. 16, Dec, 2012, pp 299 -307
[4]. Dr. R. S. Talikoti, Mr. Vinod R. Thorat, “International Journal of Engineering Research & Technology (IJERT)” ISSN: 2278-0181 www.ijert.org Vol. 3 Issue 7, July – 2014, pp 863-868
[5]. M. Botis,C. Harbic.“Bulletin of the Transilvania University of Brasov Series I: Engineering Sciences”  Vol. 5 (54) No. 1 – 2012, pp93-98
[6]. Hossein Monfared, Ayoub Shirvani, Sunny Nwaubani.“ International Journal of Civil and Structural Engineering”Volume 3, No 3, 2013, pp 451-463

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