Earth Quake Resistant Structures

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EARTH QUAKE RESISTANT STRUCTURES

ABSTRACT
Earthquake is the shaking of the ground caused by the sudden breaking and shifting of large sections of Earth's rocky outer shell. Earthquakes are among the most powerful events on earth, and their results can be terrifying. Earthquakes in general does not kill people directly. Instead, many deaths and injuries result from the collapse of buildings, bridges, and other structures. We cannot prevent natural disasters from striking, but we can prevent or limit their impact by making buildings strong enough to resist their destructive forces. This can be achieved by earth quake resistant structures. In the case of earth quakes, it is possible to neutralize their harm by applying basic engineering and planning principles that are inexpensive. This paper deals with the explanation of basic engineering and planning principles to be taken into account during the construction of earth quake resistant structures. This paper mainly deals with (i) the various types of failures that are caused due to the vibrations during the earthquakes (ii) analysis of the failures and (iii) solutions for overcoming failures.

Key words: Earth quake resistant structures, Shear joint failures, Structural failures, Non Structural failures
Site failures, Foundation failures, Lateral force resisting system.

1. INTRODUCTION
Earthquake is the shaking of the ground caused by the sudden breaking and shifting of large sections of Earth's rocky outer shell. Earthquakes are among the most powerful events on earth, and their results can be terrifying. The force of an earthquake depends on how much rock breaks and how far it shifts. Powerful earthquakes can shake firm ground violently for great distances. During minor earthquakes, the vibration may be no greater than the vibration caused by a passing truck. In order to construct earth quake resistant structures we need to analyze the way in which buildings respond towards the vibrations caused by earth quakes. These vibrations causes many failures like shear joint failures, structural failures, non-structural failures, site failures and foundation failures. In addition to this we need to analyze the lateral force resisting systems. So this paper deals with the understanding of various types of failures due to vibrations caused by earth quakes and also the analysis of the lateral forces acting on the system.

2. HOW BUILDINGS RESPOND TO EARTHQUAKES

An earthquake is the vibration of the earth’s surface that follows a sudden release of energy in the crust. During an earthquake, the ground surface moves in all directions. The most damaging effects on buildings are caused by lateral movements which disturb the stability of the structure, causing it to topple or to collapse sideways. Since buildings are normally constructed to resist gravity, many traditional systems of construction are not inherently resistant to horizontal forces. Thus design for earthquakes consists largely of solving the problem of bracing a building against sideways movement. The actions illustrated in Fig.1 demonstrate combinations of the vertical gravity effects with the lateral effects of earthquakes. [pic]

Fig.1 Effects of combining horizontal and vertical loads.
Net overturning moment = (H*L1) – (W * L2)

In most buildings this system consists in some combination of horizontal distribution elements, such as roof and floor diaphragms and vertical bracing elements such as shear walls and rigid frames. An earthquake shakes the whole building. A major design consideration must therefore be that of tying the building together to prevent it from being shaken apart. This means that the various separate elements must be positively secured to one another. The detailing of construction connections is a major part of the structural design for earth quake resistance.

2.1 Separation Joints

When the building form is complex, various parts of the building may move...
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