Expert Session

on

Effect of Earthquake on Design of Reinforced Concrete Structures

R. N. G. Patel Institute of Technology, Bardoli

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Prepared by:

Dr. Kamalsinh M. Padhiar

Head & Associate Professor

Civil Engineering Department,

R. N. G. Patel Institute of Technology, Bardoli

Outline of Presentations

• Different Layer of Earth
• Natural Disaster
• Earthquake zones in India
• Effects of Earthquake
• Major Tectonic Plates
• Causes of Earthwaves
• Types of Earthquake waves
• Seismograph
• Difference between Magnitude and Intensity
• Geography and tectonic features
• Seismic Effects of Structure on the Building
• Earthquake Resistant buildings and their Design
• Damage in the building during the Earthquake
• Strong Column Weak Beam Theory concept
• List of Indian standards
• Bands in Building Construction
• Vertical Reinforcement in Construction
• Reinforcement and Design Strategy in Beams, Columns, and Their Joints
• Shear Wall
• Ways to reduce the effects of earthquakes in building

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Different layer of earth

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Volcano

Landslides

Tsunami

Hurricane

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Earthquake Zones in India

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Effects of Earthquake

• Primary Effects

Ground break, Fault formation

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• Secondary Effects

Failure of R. C.Structures

Failure of railway, highway & bridges

Landslides and slope failure

Liquefaction and Foundation Failure

Failure of retaining walls

Tsunami

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Major Tectonic Plates on Earth’s surface

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Causes of Earthquake

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• Faults are fractures in Earth's crust where rocks on either side of the crack have slid past each other. 

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Types of Seismic Waves

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Measuring Instrument-Seismograph

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Difference between Magnitude and Intensity

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Difference between Magnitude and Intensity

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Global Occurrence of Earthquake

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• India lies at the northwestern end of the Indo-Australian Plate, which encompasses India, Australia, a major portion of the Indian Ocean, and other smaller countries.
• This plate is colliding against the huge Eurasian Plate (Figure 1) and going under the Eurasian Plate; this process of one tectonic plate getting under another is called subduction.

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Geography and Tectonic Features

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Major Earthquake in India

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Failures after Earthquake

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Railway track after the Earthquake

Failure of Express Highway in Kobe

Navalakki Port, Bhuj 2001

Ahmedabad, Bhuj 2001

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Seismic Effects on different Structures

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Seismic Effects on Structures

• When the ground moves, even the building thrown backward, and the roof experiences a force is called Intertia Force.
• The larger is the relative horizontal displacement u between the top and the bottom of column, the larger is the internal force in the column.

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Flow of Intertia force to foundation

• Under horizontal shaking of the ground, horizontal inertia forces are generated at the level of the mass of the structure (usually situated at the floor levels).

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Effect of Architectural Features of building during Earthquake

• Size of Building: In tall buildings with a large height-to-base size ratio, the horizontal movement of the floors during ground shaking is large.
• Vertical Layout of building: The earthquake forces developed at different floor levels in a building need to be brought down along the height to the ground by the shortest path; any deviation or discontinuity in this load transfer path results in poor performance of the building.

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• Adjacency of Building: When two buildings are too close to each other, they may pound on each other during strong shaking. With the increase in building height, this collision can be a greater problem. When building heights do not match the roof of the shorter building may pound at the mid-height of the column of the taller one; this can be very dangerous.

Effect of Architectural Features of building during Earthquake

R. N. G. Patel Institute of Technology, Bardoli

How building twist during an Earthquake?

• Buildings vibrate back and forth during earthquakes. Buildings with more than one storey are like rope swings with more than one cradle.
• In buildings with unequal structural members (i.e., frames and/or walls) also the floors twist about a vertical axis and displace horizontally. Likewise, buildings, which have walls only on two sides (or one side) and flexible frames along the other, twist when shaken at the ground level.

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Earthquake Resistant Building

• The engineers do not attempt to make earthquake proof buildings that will not get damaged even during the rare but strong earthquake; such buildings will be too robust and also too expensive.
• Instead, the engineering intention is to make buildings earthquake resistant; such buildings resist the effects of ground shaking, although they may get damaged severely but would not collapse during the strong earthquake. Thus, safety of people and contents is assured in earthquake-resistant buildings, and thereby a disaster is avoided. This is a major objective of seismic design codes throughout the world.

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Earthquake Design Building Philosophy

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• Under minor but frequent shaking, the main members of the building that carry vertical and horizontal forces should not be damaged; however, building parts that do not carry load may sustain repairable damage.

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• Under moderate but occasional shaking, the main members may sustain repairable damage, while the other parts of the building may be damaged such that they may even have to be replaced after the earthquake.

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• Under strong but rare shaking, the main members may sustain severe (even irreparable) damage, but the building should not collapse.

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Damage in Building

• Some cracks are avoidable but some are not avoidable.
• In a reinforced concrete frame building with masonry filler walls between columns, the cracks between vertical columns and masonry filler walls are acceptable, but diagonal cracks are not acceptable.

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Acceptable Damage: Ductility

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How to make Building Ductile for Good Seismic Performance

• In hilly areas stone masonry with mud mortar is more prevalent but in recent times it is replaced with cement mortar.

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Capacity Design Concept

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Strong Column Weak Beam Theory

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Oscillation of Building

• The building will oscillate back and forth horizontally and after some time come back to the original position.
• The time taken for each complete cycle of oscillation is the same and is called the Fundamental Natural Period T of the building.

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Indian Seismic Code List

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IS 1893(Part I),2002: Indian Standard Criteria for Earthquake resistant Design of Structure

IS 4326, 1993: Indian Standard Code of Practice for Earthquake Resistant Design and construction of Buildings

IS 13827, 1993: Indian Standard Guidelines for Improving Earthquake Resistance of Earthen buildings

IS 13828, 1993: Indian Standard guideline for Improving Earthquake resistance of Low Strength Masonry Buildings

IS 13920, 1993: Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures subjected to Seismic Forces

IS 13935, 1993: Indian Standard Guidelines for Repair and Seismic Strengthening of Buildings

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Role of Bands in Building Construction

• Bands are provided to hold the masonry building as a single unit by tying all walls together.
• Types of bands:

1) Horizontal Bands

2) Gable Bands

3) Lintel Bands

4) Plinth Bands

• IS 4326-1993 and IS 13828-1993 provide size and details of bands.
• For RCC Bands minimum thickness is required as 75 mm, and at least 2 bars of 8 mm used with 6 mm diameter bar at c/c 150 mm.

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Building with no Horizontal Band Collapse in Earthquake

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Building with Bands

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Vertical Reinforcement in Masonry Building

• When the ground shakes the inertia force causes small-sized masonry wall piers to disconnect from the masonry above and below.
• The rocking of a masonry pier can crush the masonry at the corners.
• Rocking is possible when masonry piers are slender, and when weight of the structure is small otherwise it is fail in the x type or diagonal cracking.

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Vertical Reinforcement in Building

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How earthquake Affect Reinforced Concrete Structures

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• For a building to remain safe during earthquake shaking columns should be stronger than beams, and foundations should be stronger than columns.
• In Earthquake prone areas to construct building three components should be effectively designed like: Beams, Columns, and Beam Column Joints.

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Reinforcement and Design Strategy in Beams

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Reinforcement and Design Strategy in Beams

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Reinforcement and Design Strategy in Columns

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Reinforcement and Design Strategy in Columns

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Reinforcement and Design Strategy in Beam Column Joint

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Reinforcement and Design Strategy in Beam Column Joint

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Shear Wall Building

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• Reinforced concrete buildings often have plate-like RC walls called Shear Wall.
• Thickness of the shear wall can be as low as 150 mm, or as high as 400 mm in high-rise buildings.

Advantages of Shear Wall:

• Easy to construct because reinforcement detailing of walls is relatively straightforward and therefore easily implemented at the site.
• Shear walls are efficient, both in terms of construction cost and effectiveness in minimizing earthquake damage in structural and non-structural elements.

R. N. G. Patel Institute of Technology, Bardoli

Architectural aspects of Shear Wall

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• Reinforcement details and design consideration of the shear wall is provided in the IS: 13920-1993.

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Ways to Reduce the Effects of Earthquake in Buildings – Base Isolation

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Ways to Reduce the Effects of Earthquake in Buildings – Seismic Dampers

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• Dampers work as a hydraulic shock absorbers of the cars.
• When seismic energy is transmitted through the dampers, dampers absorb part of it and thus dampen the motion of the building.
• Dampers are used since the 1960s.
• In India generally friction dampers are used.

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