Basic Training Course on Earthquake Engineering

How Seismic Forces are Resisted Lecturer: Dr Zuhal OZDEMIR Department of Civil and Structural Engineering

University of Sheffield

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Basic Training Course on Earthquake Engineering

Outline Static and Dynamic Loads Seismic Loads Earthquake Design Philosophy Earthquake Response of Structures Earthquake records Equivalent simple system Response spectrum

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Basic Training Course on Earthquake Engineering

Static Loads

Dead loads are those have unchangeable locations in structure and their values are certain and constant Live loads are those movable and their values are uncertain.

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Basic Training Course on Earthquake Engineering

Dynamic Loads Dynamic loads are function of time

Blast load

Impact load

Wind load

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Seismic load

Basic Training Course on Earthquake Engineering

Wind vs Seismic Loads Wind loading - force-type loading (for most buildings static) Seismic actions- ground displacement-type (for most buildings dynamic)

(a) Earthquake Ground Movement at base, and (b) Wind Pressure on exposed area

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Basic Training Course on Earthquake Engineering

Seismic Loads Seismic loads induces inertia forces on the structure.

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Basic Training Course on Earthquake Engineering

Earthquake-resistant design philosophy Normal buildings should be able to resist: (a) Minor (and frequent) shaking with no damage; (b) Moderate shaking with minor damage; and (c) Severe (and infrequent) shaking with NO collapse (to save life and property inside/adjoining the building).

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Basic Training Course on Earthquake Engineering

Earthquake Response

Seismic response of the building is controlled by: - Characteristics of structure itself - Characteristics of earthquake motion - Characteristics of the underlying soil

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Basic Training Course on Earthquake Engineering

Earthquake records

Amplitude Duration Frequency content PGA: Peak Acceleration

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Ground

Basic Training Course on Earthquake Engineering

Equivalent simple structure

A single-degree-of-freedom structure has mass m, stiffness k and associated structural damping ξ.

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Basic Training Course on Earthquake Engineering

Dependence of Response on Natural Period

The seismic response of structures with different periods to the same ground motion will be different. http://www.shef.ac.uk/~tmrnet

Basic Training Course on Earthquake Engineering

Response spectrum

Influence of same ground motion on buildings with different fundamental period http://www.shef.ac.uk/~tmrnet

Basic Training Course on Earthquake Engineering

Response spectrum

Influence of same ground motion on buildings with different fundamental period http://www.shef.ac.uk/~tmrnet

Basic Training Course on Earthquake Engineering

Response spectrum

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Basic Training Course on Earthquake Engineering

Response spectrum

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Basic Training Course on Earthquake Engineering

Elastic Seismic Design Forces Usual seismic design of structures is performed using the maximum force induced in the structure due to earthquake shaking. F = m ag F: Horizontal seismic force acting at the base of the building.

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Basic Training Course on Earthquake Engineering

Elastic Seismic Design Forces For regular structures, vertical distribution pattern of the earthquake forces along the structures is assumed to be in proportional to the deformation shape of the structure.

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Basic Training Course on Earthquake Engineering

Capacity Design Method We design our structure in a way that damage occurs at predefined locations instead of everywhere or arbitrary locations in the structure.

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Basic Training Course on Earthquake Engineering

Earthquake-resistant design philosophy Design the building to remain elastic or to undergo inelastic behaviour.

Structural properties: Stiffness, strength, ductility. http://www.shef.ac.uk/~tmrnet

Basic Training Course on Earthquake Engineering

Earthquake-resistant design philosophy In seismic design, there are two options, design the building to remain elastic or to undergo inelastic behaviour (damage). The latter option is adopted in normal buildings, and the former in special buildings, like critical buildings of nuclear power plants.

(a) Special structures, and (b) ordinary structures

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Basic Training Course on Earthquake Engineering

Earthquake-resistant design philosophy Calculate maximum elastic forces and reduce by a factor to obtain design forces. Damage is expected during an earthquake in normal constructions. the structure should maintain load bearing capacity while it undergoes reversals of inelastic deformations under seismic response.

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Basic Training Course on Earthquake Engineering

Earthquake-resistant design philosophy The design for only a fraction of the elastic level of seismic forces is possible, only if the building can stably withstand large displacement demand through structural damage without collapse and undue loss of strength. This property is called ductility.

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Basic Training Course on Earthquake Engineering

Simplicity, compactness and symmetry in plan layout

Good

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Bad

Basic Training Course on Earthquake Engineering

Continuity and regularity in elevation

Good

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Bad

Basic Training Course on Earthquake Engineering

Regular Foundations

Good

loose Firm

Bad

loose Firm

loose

loose

Firm

Firm

loose Firm

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