Final Project Report of Base Isolation

CHAPTER 1 INTRODUCTION 1.1 Background:

Recent years have seen a number of occurrences of catastrophic structures failure due to severe seismic events i.e. earthquakes. The huge earthquakes in Chile and Haiti that lead to a large number of death tolls and massive loss of properties are the examples. Nepal is too vulnerable to the disasters. So, it has been a great concern of all to make seismically strong structures. One of the widely implemented and accepted seismic protection systems is base isolation. Base isolation is an emerging approach that that is supposed to avoid the forces imposed on structures during earthquake the fundamental concept is to isolate a structure. The fundamental concept is to isolate a structure from ground motion, especially in the frequency range where the building is most affected. The goal is to reduce interstory drifts and floor accelerations to limit damage to the structure and its contents in a cost-effective manner. For simple buildings, base- friction isolation maybe achieved by reducing the coefficient of friction between the structure and its foundation, or by placing a flexible connection between the structure and its foundation. For reduction of the coefficient of friction between the structure and its foundation, one suggested technique is to place two layers of good quality plastic between the structure and its foundation, so that the plastic layers may slide over each other. However still a lots of concerns are there regarding its efficacy. It has been observed that base-isolated buildings are vulnerable to strong impulsive ground motions generated at near-fault locations. Also flexible connections between the structure and its foundation are also difficult to achieve on a permanent basis.

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1.2 Objectives:

 To prepare earthquake resistant building.  To analyze the seismic effect on base-isolated structure.  To study the strength and applicability of base-isolation system.

1.3 Methodology: We have constructed two models of building, one with base isolation and the other general model , both fixed on base plywood. Cutting, drilling and welding were the major process gone through to develop the required models. 1.4 Rationale need for study: Nepal is geographically very vulnerable to earthquakes. The poor structural strength of buildings in rural areas greatly exacerbates the effects. Lots of major earthquakes have caused much causality. Recent observations of seismic vibration clearly give an indication that another major event would be a catastrophic. It is impossible to prevent the upcoming disaster but our small attention towards the strength of structures can decrease the effects and the lives can be saved. A simple, appropriate solution involving locally available materials may provide a significant improvement to the current situation.

1.5 Overview of the report: This report is the overall explanation about the project model we have accomplished in six months duration in the mechanical workshop. This report also includes diagrams and CAD models of our project. To sum up, this report is a complete overview of our project.

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CHAPTER 2 LITERATURE REVIEW

The idea that a building can be uncoupled from the damaging effects of the ground movement produced by a strong earthquake has appealed to inventors and engineers for more than a century. Many ingenious devices have been proposed to achieve this result, but very few have been tried and the concept now generally referred to as base isolation or seismic isolation has yet to become acceptable to the engineering profession as a whole. •

Over 1000 buildings across the world have been equipped with seismic base isolation

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In India base isolation technique was first demonstrated after 1993 Killari EQ

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Two single storey building (one school and another shopping complex building) were built with rubber base isolators resting on hard ground

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The four storey Bhuj hospital building was built with base isolation technique after 2001 Bhuj EQ

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Fig. 2: base isolated in a building of Tokyo

Fig 1: view of basement of Bhuj Hospital (Source:encylopedia)

CHAPTER 3 DISCUSSION Following is the description about the process involved, time period and physical description about our project.

3.1 Collection of materials: The required materials for model construction were 1. Gabion rod:( for beams, column and base) 2. Ply wood:( for supporting base and foundation) 3. Iron sheet:( for raising the column and ceiling development) 4. Roller :( for isolation) 5. Rivet 6. Enamel paints

3.2 Model construction: 3.2.1 Foundation development: For the development of foundation, we have used the ply wood of thickness (18 mm). As both the model with base-isolation and without base isolation should be placed together in

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the shake table for demonstration, we have made it of dimension (516mm x 630mm) for that purpose. For the building model foundation we have used the ply wood of thickness (8 mm) of dimension (250mm x 250mm) for both the models. 3.2.2 Structure development For the development of structure, we have used the gabion rod of diameter (3mm). As it was stiff enough for supporting the weight of roof, we decided to use single rod for each column. To make the column fixed we used iron sheet of small length about (35 mm) and drilled 3 hole of diameter (3mm). Riveting was done in order to fix the iron sheet with the ply and in the centre hole the gabion rod was made fixed by welding. 3.2.3 Slab development The weight of the ceiling should be high enough in order to make the deflection visible prominently. For this we used heavy metal sheet of dimension (245mm x 250mm). The iron sheet was made fixed with the column (gabion rod) by using arc welding. 3.2.4 Base isolation Since the base isolation for real structures are achieved by using rubber pad, for simplicity we used roller just to show the pattern of vibration during seismic effect. Four rollers were used each separated by a distance 158mm along breadth and 185mm along length. We rest the base of the building above the roller so that any shake could move the whole model to and fro thereby minimizing the vibration on its structure. 3.2.5 Fixing the models For fixing the base isolated model we tied the column with the help of elastic rubber to bolt at an angle of 70 degree for its free movement. However we fixed the general model with the help of nut and bolt fastened to the base. 3.2.6 Painting the model In order to make the model attractive and give fineness to it, we painted the model with different colors. 5

3.3 Time Period The project started from 22 March 2010 and completed on 28 June 2010. It took 12 weeks to complete the project.

3.4 Testing At first the two models were placed in the shaking table. A horizontal force was applied to create the shaking motion. The base isolated model did not show any deflection in its column rather the structure shifted as a whole. Whereas the general model showed the deflection in its column. Since the deflection was not prominent, to obtain an observable deflection we placed a weight of 5 kg on the floor of model with base isolation and on slab of general model. This made our test more realistic as actual buildings have huge amount of weight. The practicability of base isolation to make the building earthquake resistant was hence realized by us.

3.5 Technical and Physical Description

Model structure

Dimensions( in mm)

Thickness(in mm)

1.Base(for fixation)

516 x 630

18

2. Foundation base

250 x 250

8

2.Column

270

ϕ3

3.Ceiling

245 x 250

2.5

Overall model dimension: (250mm x 250mm x 270mm) , weight:2 kg 6

3.6 Process of working As the horizontal force is applied on the base plywood, we can observe deflection both in case of isolated structure and general structure. However, the column of general model drags the slab due to inertial force and the isolated structure moves along thereby causing no any effect on columns.

4. Cost Estimation

4.1 Material Cost S.No. Items(Specification)

Cost per unit(NRs)

No. items

of Total cost(NRs)

1 2

Plywood( thickness 8) Plywood( thickness 18)

75 225

2 1

150 225

3 4 5 6 7 8 9

Roller Gabion rod Elastic rubber Nut and bolt Metal sheet( slab) Rivets Iron sheet(for fixation)

50 50 45 5 150 20 40

4 1 1 30 2 2 1

200 50 45 150 300 40 40

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10

Enamel paint

150 Total(a1)

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4.2 Miscellaneous Cost: a)

Travelling Cost: 150(NRs)

b)

Printing Cost: Report=25 pages*3=75(NRs) Proposal=10 pages*3=30(NRs)

4.3 Gross Total: a1+4.2(a)+4.2(b)=1605(NRs) 5. Problems encountered  Problem in finding the material as per dimension  No proper welding in gabion rod  Problem in drilling small holes in thick metal sheet  Problem in making the proper contact of roller with the ply

6. Conclusions 

Inertia is the major factor for buildings destruction.

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Earthquake resistant building can be obtained by isolating base and its structure.

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Base isolation is applicable to low to medium rise building.

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150 1350

FIGURES

Fig 3: isometric view of general model

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Fig 4: front view of general model

Fig 5: top view of general model

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Fig 6: top view of base isolated model

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Fig 7: front view of base isolated

Fig 8: top view of base isolated model

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Fig 9: roller used for isolation

Fig 10: base isolated model shifted( left) and general model deflected(right)

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Fig 11: final model

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Model with base isolation using roller

Deflection in general model