EQ ARCH 2003-Version
Transcript of 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.
EARTHQUAKE MAGNITUDE AND INTENSITY
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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.
EARTHQUAKE MAGNITUDE AND INTENSITY
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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