EQ ARCH 2003-Version

7/29/2019 EQ ARCH 2003-Version

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IMPORTANCE OF ANARCHITECTURAL DESIGN

ON BEHAVIOUR OF THE BUILDINGDURING EARTHQUAKE

Sumant B. PatelStructural Engineering Department

B.V.M. engineering collegeVallabh Vidyanagar


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Soil

Flow of seismic inertia forces through all structural components.

Earthquake Shaking

Floor Slab

Walls

and/orColumns

Foundations

Inertia Forces


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It is the total design lateral force at the base of astructure.

VB = AhW

BASE SHEAR

Where,

Ah =Horizontal Seismic Co-efcient

(Explained in subsequent slides)

W =Seismic weight of the building


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HORIZONTAL SEISMIC CO-EFFICIENT

Where,

Z = Zone factor

I = Importance factor

R = Response reduction factor

Sa/g= average response acceleration co-e

fcient


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It is a factor to obtain

the design spectrum

depending on the

perceived maximum

seismic risk

characterized by

Maximum Considered

Earthquake (MCE) in the

zone in which the

structure is located. The

basic zone factors

included in this standard

are reasonable estimate

of e

ective peak groundacceleration.

ZONE FACTOR (Z)


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A major diference between the earthquake

intensity and magnitude lies in the fact that

magnitude of an earthquake is determined based on

measuring the ground motion with instruments

(seismographs), whereas the intensity of an

earthquake is determined based on observations of

earthquake eects on building structures and human

perceptions.

EARTHQUAKE MAGNITUDE AND INTENSITY


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Another essential diference between a magnitude

and intensity of an earthquake lies in the fact that

magnitude is a unique indicator of a size of an

earthquake - each earthquake is characterized with a

single value which indicates its magnitude. At the

same time, each earthquake is characterized with

various intensities, depending on the location of aparticular site with respect to the epicenter.



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Bright(100 lumens)

Normal(50 lumens)

Dull(20 lumens)

Near

Far

Reducing illumination with distance from an electric bulb

100 Watt Bulb


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For example, Canada's largest historic earthquake,

the Queen Charlotte Island earthquake of August

22, 1949 was characterized with magnitude 8.1 on

the Richter scale. The same earthquake was

characterized with MMI intensities ranging from III to

over VII, as illustrated in the figure in next slide.



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As an illustration of MMI intensity of VII or higher in the area close tothe epicenter of this earthquake "cows were knocked o their feet,

and a geologist with the Geological Survey of Canada working on the

north end of Graham Island could not stand up. In Prince Rupert

(MMI intensity VI), "windows were shattered and buildings swayed."


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It is a factor used to obtain the design seismic

force depending on the functional use of the

structure, characterized by hazardousconsequences of its failure, its post-earthquake

functional need, historic value, or economic

importance.

e.g : hospitals; schools; monumental structures;

emergency

buildings like telephone exchange etc.

IMPORTANCE FACTOR (I)


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RESPONSE REDUCTION FACTOR (R)

It is the factor by which the actual base shear

force, that would be generated if the structure

were to remain elastic during its response to

the Design Basis Earthquake (DBE) shaking

shall be reduced toobtain the design lateral

force.

It depends on the perceived seismic damage

performance of the structure, characterized

by ductile or brittle deformations.

It is a discount factor. If the building is more

ductile, it attracts more force.

Ratio (I/R) shall not be greater than 1.0


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AVERAGE RESPONSE ACCELERATION CO-EFFICIENT(Sa /g)

It depends on types of Soil and time period of thebuilding.

e.g. : Hard Soil (Rocky) , Medium Soil and Soft Soil


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CENTRE OF MASS

The point through which the

resultant of the masses of a

system acts. This point

corresponds to the centre of

gravity of masses of system.


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20m

8m

4m

10m

20 kN/m2

10 kN/m2

I II

III

Let origin be at point A, and the coordinates of the centre ofmass be at (X, Y)

Total mass = M1

+ M2

+ M3

= 20x10x4 + 10x10x4 + 10x20x4

(Weight) = 800 + 400 + 800

= 2000kN

X = (800x5 + 400x15 + 800x10) / (2000) = 9.0 m= =

A

CENTRE OF MASS

CoM = (9.0, 6.8)


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CENTRE OF STIFFNESS

The point through which

the resultant of the

restoring forces of a

system acts.


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CENTRE OF STIFFNESS

20m

8m

4m

10m

A

Let Column stiness about X-direction is 4k and about Y-

direction is k

Therefore,

k1 = k2 = 3k and kA = kB = kC = 8k

2

1

A B C

CoS = (10.0, 4.0)

1m

2.8m


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CENTRE OF STIFFNESS

20m

8m

4m

10m

A

2

1

A B C

1.4

7m

k1 = 3k, k2 = 6k and kA = kB = 8k, kC = 5k

X = (8k x 10 + 5k x 20) / ( 8k + 8k + 5k) = 8.57mY = (6k x8) / ( 3k + 6k) = 5.33m

CoS = (8.57, 5.33)

Eccentricitiesex = 0.43m

ey = 1.47m


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ECCENTRICITY (CENTER OF MASS)

Rope swings and buildings, both swing back-and-forth when shaken horizontally. The formerare hung from the top, while the latter are raisedfrom the ground.

(a) Single-storey building (b) Three-storey building

Even if vertical members are placed uniformly in planof building, more mass on one side causes the floorsto twist.

Earthquake GroundShaking

Twist

Light Sideof Building

Heavy Sideof Building


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ECCENTRICITY(CENTER OF STIFFNESS)

Buildings have unequal vertical members; theycause the building to twist about a verticalaxis.

Vertical Axis aboutwhich building twists

EarthquakeGroundMovement

(b) Building on slopy ground

(a) Swing with unequal ropes

(c) Buildings with walls on two/one sides (in plan)

Wall

Columns

Columns

Wall

Wall

One-side open ground storey building twists during

earthquake shaking.

EarthquakeGroundShaking

These columns are more vulnerable

Vertical members of buildings that move morehorizontally sustain more damage.

EarthquakeGround

Movement


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Shear wall is a stielement and attracts

more forces.

Ideally, Shear wallshould be on theperiphery.

Reinforced concrete shear walls in buildings an excellent structuralsystem for earthquake resistance.

RC Walls

Plan

RC

ShearWallFoundation

SHEAR WALL


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8m

A

B

A

1 4 72 3 5 6

SHEAR WALL

k1 = k2 = = k7 = 8k

ki = 56

F1 = F2 = F3 = = F7 = (ki / k ) x F = (8/56) x 100 =

F = 100kN

20m


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SHEAR WALL20m

8m

A

B

A

1 4 72 3 5 6

F = 100kNk1 = k7 = 120k , k2 = k3 = = k6 = 8k

ki = 2 x 120k + 5 x 8k = 240k + 40k = 280k

F1

= (120/280) x 100 = 42.86 kN ,

F2 = (8/280) x 100 = 2.86 kN


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A FIELD EXAMPLE


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How Architectural FeaturesAfect Buildings During

Earthquakes?


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If we have a poor configuration to start

with, all the engineer can do is to provide a

band-aid - improve a basically poor

solution as best as he can. Conversely, if we

start-o with a good configuration and

reasonable framing system, even a poor

engineer cannot harm its ultimate

performance too much.

- Henry Degenkolb,

Earthquake Engineer ,USA

CONFIGURATION


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CONFIGURATION

Buildings with one of their overall sizes much larger or much smallerthan the other two, do not perform well during earthquakes.

(b) too long

(c) too large in plan(a) too tall

Simple plan shape buildings do well during earthquakes.

(a) Simple Plan

::good

(b) Corners

and Curves

:: poor

(c) Separation joints make complex plans intosimple plans


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Sudden deviations in load transfer path along the

height lead to poor performance of buildings.

(a) Setbacks

(b) Weak or Flexible Storey

(c) Slopy Ground (d) Hanging or Floating Columns

Unusually

Tall

Storey

ReinforcedConcrete WallDiscontinued inGround Storey

(e) Discontinuing Structural Members

CONFIGURATION


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Pounding can occur between adjoining buildings due to horizontalvibrations of the two buildings.

Fus

e

POUNDING

d = 200mm

approx

d = 1+

2

Floor ofBuilding 1

Floor ofBuilding 2


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SHORT COLUMN EFFECT

Buildings with short columns two explicit examples of common occurrences.

Regular ColumnShort Column

Mezzanine Floor

Tall Column

Sloped Ground

(b)

(a)


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Opening

RegularColumn

PartialHeight

Wall

Shortcolumn

Short columns effectin RC buildings when partial height wallsadjoin columns the effect is implicit here because infill walls areoften treated as non-structural elements.

Portion ofcolumnrestrained frommoving

SHORT COLUMN EFFECT

Short columns are stiffer and attract larger forces duringearthquakes this must be accounted for in design.

Short Column:Attractslarger horizontal force

Tall Column:Attractssmaller horizontalforce

Long

Short


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Slum area

A A

ROAD

3 m

0.6m

SECTION A-A

k1 = 12EI / L13 = 12EI /

33

k2 = 12EI / L23 = 12EI /

0.63

W W W W

SHORT COLUMN EFFECT


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SHORT COLUMN EFFECT

Effective height of column over which itcan bend is restricted by adjacent wallsthis short-column effect is most severe whenopening height is small.

Short columnbetween linteland sill ofwindow

Source: Wakabayashi,M.,Design ofEarthquake-Resistant Buildings, McGrawHill Book Company, New York, USA


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REFERENCES

1) IS:1893 (Part1) 20022) Earthquake Tips, IIT Kanpur and BMTPC -New Delhi

3) British Columbia Institute of Technology

http://commons.bcit.ca/civil/students/earthquakes/

unit1_03.htm


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THANK YOU

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