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PRESENTED BYS.BHARANI

S.SUBITCHAPRE-FINAL YEARS

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Earthquake is the worst of all natural disasters.

The various techniques be adapted to make the buildings more resistant.

Due to shaking of the ground , base of the building will experience motion & tendency of roof is to stay in its original position due to inertia force.

Due to wall and column connection, the force will drag the roof along with them.

So its tendency is to attack from the base and at beam column joint and protrude through structure.

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GENERAL DESIGN PHENOMENONBeam Column Effect

For higher zones strong column and weak beam are better. Beam damage will cause localized effect whereas the column

damages it leads to entire structural damage.

Joint displacement due to seismic waves Column Failure

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Inverse Pendulum Effect

The parking area do not have any partition walls

It is too weak to carry earthquake force

Design Phenomenon

Stiff masonry walls are avoided and bare frames are considered in design calculations.

Steel sections will be raised as vertical reinforcement and hollow blocks as partitions hence the inverted pendulum effect is not captured

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Beams as a Structural Member Beams are the horizontal members in a structure.

It has two types of failure.

flexural failure Shear Failure

Column as a structural member: Columns, the vertical members in RC buildings, contain two

types of steel reinforcements.

Long straight bars placed vertically along the length to sustain axial force and transverse ties placed horizontally at regular intervals along its full length.

Columns can sustain two types of Damage axial-flexural Failure shear failure.

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Horizontal Bands and its Role It holds a masonry building as a Single unit by tying all the

walls together.

There are four types of bands in a typical Masonry building, namely

1. gable band -employed in pitched or sloped roofs.

2.roof band, not required R.C or reinforced brick roofs , but used in pitched or sloped roof.

3.lintel band -since it ties the walls together and also breaks the monotonous continuity of wall.

4.plinth band- Used in uneven settlement of foundation in soil .

It will be better to use RC bands

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Shear Wall vertical plate-like RC walls called Shear Walls. Their thickness varies from 150mm to 400mm.

Shear walls are like vertically-oriented wide beams that carry earthquake loads downwards to the foundation.

It provide around the elevator core or stair well is known as shear core.

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Edges of shear walls experience high compressive and tensile stresses due to overturning effect.

To ensure that shear walls behave in a ductile way, concrete in the wall end regions must be reinforced in a special manner to sustain these load reversals without loosing strength

End regions of a wall with increased confinement are called boundary elements which have high bending strength.

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Shorter columns suffered more damage as compared to taller column.

Because of same cross-section move horizontally

the short column is stiffer,it attracts larger earthquake force and X-shaped cracks.

 Stiffness of a column means resistance to deformation

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Design Phenomenon: this effect must be addressed in structural design

the reinforcement must extend beyond the short column into the columns vertically above.

the width has to be increased in stone or brick masonry.

Beam Column Joint more strength is not expected when both materials are same.

have to take care on these unavoidable joints.

During earthquake the upper bars and lower bars act in a different direction causing elongation or damage of joint.

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Design StrategyIn design practice large column size, having large closed loops are placed inside.

The anchoring of the bars at the ends and Micro concreting in the congested junction.

Hidden Beams They are concealed beams having their depth equal to that of the slab

The load carrying capacity increase to 135% with an economical increase of just 0.4 – 0.5%.

These beams are designed for negative bending moment

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As moment increases, the linear stress distribution form persists

The extreme fiber stress reaches the yield stress value.

Further increase in the bending moment cannot produce any increased fiber-stress and

Finally fibers reach the yield stress the section will yield and the complete yielding is termed as plastic hinge.

The section now carries the maximum bending moment without strain hardening taking place.

The beam will behave as if it is hinged at the plastic section and a condition of collapse has been reached.

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Reduced Beam Section This is provided along the length of steel beams. their area of cross section lesser than the proceeding section that it will

act as a plastic hinge.

In case of steel section also a circular arc will be cut in the required flange portion of span.

 

 

Reduced Beam Section  

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The lateral thrust will be more in domes and shells. We will be having a thin walled cylindrical tube of diameter about 10

to 15 cm and steel rods Then stressing will be done as per design and then the micro concrete

is injected in pressure into the tube.

Techniques to Adopt on Sky Scrappers In large multistoried buildings provide as Bearing, Bracing, Friction

pendulum and Dampers instead of beams, columns, and other structural elements to take Vibration produced by lateral force.

Pre tensioning Technique

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Rubber Bearings

Rubber bearing are made from layers of rubber, a thick steel plate between the thin steel plates .

Placed between the bottom of a building and its foundation. The bearings to be strong for vertical load Weaker for horizontal loads, so that they can move

sideways due to lateral thrust.

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Viscous Dampers

It is shock absorbers.

Containing closed cylinder with viscous fluid and a piston.

As the piston move in and out of the cylinder oil is forced in and out causing friction cause building sway.

The damper is usually installed as part of a building's bracing system.

Friction Dampers

They are designed to have moving parts which slide over each other.

The damper is made up from a set of steel plates.

At forces,the plates can slide creating friction causing energy dissipation.

The plates are specially treated to increase the friction between them.

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Cross Bracings

It is common vertical load distribution.

But we can also adopt this technique to foundation

It will distribute the load to joints and through foundation finally.

Friction Pendulum:

In large multistory buildings, we can always expect some appreciable movement in it base due to the vibration

. to resist completely we can allow the structure to deform at its foundation level by provision of friction pendulum

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Constraint is that, human has to satisfy his unlimited wants through limited resources.

As a part of the civil engineering world, we all have a role to play in developing newer and more effective techniques to increase the seismic resistance of buildings to make them invulnerable to an appreciable intensity of earthquakes

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Reference

•MCEER Information Service

•IS 1893 – 2002 CRITERIA FOR EARTHQUAKE RESISTANCE DEGIN OF STRUCTURES

•EARTHQUAKE RESISTANCE TIPS – IITK- bmptc

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