Earthquake

Engineering

Presented By :

MAK KHAN SIPONDept. of Civil Engineering,Reg. No: 09105064

What is Earthquake engineering?

Earthquake engineering is the application of civil engineering to reduce life and economic losses due to earthquakes.

Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading.

What is Seismic loading ?

Seismic loading means application of an earthquake-generated excitation to a structure (or geo-structure). It happens at contact surfaces of a structure either with the ground , or with adjacent structures  or with gravity waves from tsunami.

Seismic loading depends primarily on:

• Probable earthquake's parameters at the site (seismic hazard)

• Geotechnical parameters of the site

• Structure's characteristics

• Characteristics of the expected gravity waves from tsunami (if applicable)

Seismic performance • Seismic performance defines a structure's ability to sustain

its due functions, such as its safety and serviceability, at and after a particular earthquake exposure. A structure is, normally, considered safe if it does not endanger the lives and well-being of those in or around it by partially or completely collapsing. A structure may be considered serviceable if it is able to fulfill its operational functions for which it was designed.

What are the Failure modes?

 The major reasons of failure :

• Unreinforced masonry building

• Soft story effect

• Soil liquefaction

•  Insufficient shear reinforcement

Unreinforced masonry building

• The lack of reinforcement coupled with poor mortar and inadequate roof-to-wall ties can result in substantial damage to a unreinforced masonry building.

Soft story effect• Absence of adequate shear walls on the ground level caused

damage to this structure.

Soil liquefaction Soil liquefaction. In the cases where the soil consists of loose granular deposited

materials with the tendency to develop excessive hydrostatic pore water pressure of sufficient magnitude and compact, liquefaction of those loose saturated deposits may result in non-uniform settlements and tilting of structures. This caused major damage to thousands of buildings in Niigata, Japan during the 1964 earthquake.

 Insufficient shear reinforcement

Reinforced concrete column burst  due to insufficient shear reinforcement mode which allows main reinforcement to buckle outwards.

Some Simple Design Criteria

Simple Design Criteria• Choose an adequate lateral load resisting system.

An adequate lateral load resisting system

Simple Design Criteria

• Choose an adequate lateral load resisting system.

• Maintain regularity in elevation.

Maintain regularity in elevation

Simple Design Criteria• Choose an adequate lateral load resisting system.

• Maintain regularity in elevation.

• Ensure connection between structural elements.

Ensure connection between structural elements

Ensure connection between structural elements

Simple Design Criteria

• Choose an adequate lateral load resisting system.

• Maintain regularity in elevation.

• Ensure connection between structural elements.

• Avoid designing in locations of stress concentration.

Avoid designing in locations of stress concentration

Simple Design Criteria• Choose an adequate lateral load resisting system.

• Maintain regularity in elevation.

• Ensure connection between structural elements.

• Avoid designing in locations of stress concentration.

• Spacing between buildings to avoid pounding.

Avoid pounding

Simple Design Criteria• Choose an adequate lateral load resisting system.

• Maintain regularity in elevation.

• Ensure connection between structural elements.

• Avoid designing in locations of stress concentration.

• Spacing between buildings to avoid pounding.

• Adopt capacity design concepts to control the failure mode.

Capacity Design Concepts

Capacity Design Concepts

• An earthquake-resistant building has a number of special structural features. Interior support walls called shear walls, made of reinforced concrete, strengthen the structure and help resist rocking forces. Shear walls in the center of a building form a shear core. Cross-bracing reinforces walls with diagonal steel beams. Base isolators act as shock absorbers, and a moat allows a building to bend.

Shear wall and shear core

• Shear wall and shear core are walls those made of reinforcement concrete which are more stiffer and stronger that gives the structure more strength against the lateral load.

Base Isolation

• A base isolated structure is supported by a series of bearing pads which are placed between the building and the building's foundation.

• A variety of different types of base isolation bearing pads have now been developed.

Example: Lead–rubber bearings, Spherical Sliding Isolation Systems

Lead–Rubber Bearings

• Lead–rubber bearings. These are among the frequently–used types of base isolation bearings. (See Figure) A lead–rubber bearing is made from layers of rubber sandwiched together with layers of steel. In the middle of the bearing is a solid lead "plug." On top and bottom, the bearing is fitted with steel plates which are used to attach the bearing to the building and foundation. The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction.

Earthquake Generated Forces

•To get a basic idea of how base isolation works, first examine Figure. This shows an earthquake acting on both a base isolated building and a conventional, fixed–base, building. As a result of an earthquake, the ground beneath each building begins to move. In Figure , it is shown moving to the right .

Spherical Sliding Isolation Systems

Lead–rubber bearings are just one of a number of different types of base isolation bearings which have now been developed. Spherical Sliding Isolation Systems are another type of base isolation. The building is supported by bearing pads that have a curved surface and low friction. During an earthquake, the building is free to slide on the bearings. Since the bearings have a curved surface, the building slides both horizontally and vertically The force needed to move the building upwards limits the horizontal or lateral forces which would otherwise cause building deformations. Also, by adjusting the radius of the bearing's curved surface, this property can be used to design bearings that also lengthen the building's period of vibration.

Tuned mass damper

• Typically, the tuned mass dampers are huge concrete blocks mounted in sky scrapers or other structures and moved in opposition to the resonance frequency oscillations of the structures by means of some sort of spring mechanism.

Building elevation control• Building elevation control is a

valuable source of vibration control of seismic loading. Pyramid-shaped skyscrapers continue to attract attention of architects and engineers because such structures promise a better stability against earthquakes and winds.

Springs-with-damper base isolator

• It is a base isolation device conceptually similar to Lead Rubber Bearing.

Advantages And Disadvantages

Braced frameAdvantages

•Usually used in steel structures

•Add great amount of stiffness to structure

•Simple to design and analyze

Disadvantages

•May require special tools to install

•Not energy efficient (steel)•Steel is easy to transfer heat. So, it’s easy to lose heat during winter

•Cannot adapt to different load conditions

Braced frameAdvantages

•Usually used in steel structures

•Add great amount of stiffness to structure

•Simple to design and analyze

Disadvantages

•May require special tools to install

•Not energy efficient (steel)•Steel is easy to transfer heat. So, it’s easy to lose heat during winter

•Cannot adapt to different load conditions

Shear wallMany materials are used as shear wall

Woods, steel, concrete and masonry

Commonly used in homes

Advantages

•Provides great stiffness

•Easy to install to existing structures

•Many constructors are familiar with it

•Cheap

Disadvantages

•Less energy dissipation

•Cause higher loses to non-structural components

Base isolator Advantages

- High energy dissipation

- Not required electric

- Good for using in large structures

- Compact

- Have both lateral stiffness and Vertical support

Disadvantages- Difficult to install to existing structures

- Provides lower stiffness

- Sensitive to near fault ground Acc.

Objective of the Presentation

Objective of the Presentation• The main objective of this

presentation is to introduce earthquake engineering, how it works, why it is needed and also to share the fundamental concepts that we try to gather.

Thank You All

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