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SEISMIC ANALYSIS
To generate forces on the structure due to base motion arisingfrom earthquake.
Structural
response
Verticalmotion
or zon amotion
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
1
SEISMIC ANALYSIS
API RP 2A IS 1893
STRENGTH LEVEL EQ
(200 YEARS)
DESIGN BASIS EQ
(DBE)
DUCTILITY LEVEL EQ(2000 YEARS)
MAXIMUMCONSIDERED EQ
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
2
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SEISMIC ANALYSISGEOMETRY
ANDSEASTATE
LINEARISE
SOIL MODELPSI INPUT
FILE
SUPERELEMENT
DYNAMIC ANALYSIS
& FREQUENCIES
DYNAMIC RESPONSERESPONSE
SEISMICSPECTRASPECTRA METHOD API IS 1893
LOAD COMBINATIONMODEL: CQC
NUMBER CHECKPRST 1.0
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
3
SEISMIC ANALYSIS
Peak Ground Acceleration (PGA) Indication of Strengthof earthquake
PGA = 0.3 X Spectral average between period 0.1 to 0.3sec.
Structure
PGA
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
4
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SEISMIC ANALYSIS
AS PER IS: 1893-2000
ZONE SEISMIC
INTENSITY
ZONE
FACTOR.
III Moderate 0.16
.
V Very 0.36
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
5
SEISMIC ANALYSIS
ar qua e es gn r er a
Specific design criteria depends on the country, location andtype of soil stratum etc.
IS 1893
.
Maximum Considered Earthquake (MCE)
API RP 2A
Strength Level Earthquake (SLE)
Ductilit Level Earth uake DLE
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
6
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SEISMIC ANALYSIS
ar qua e es gn r er a
OPERATIONAL EARTHWUAKE (200 YEARS RETURN PERIOD)
conventional structural design Allowable stresses can be increased
EXTREME EARTHQUAKE (2000 YEARS RETURN PERIOD)
structure to be stable
Redundant framing
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
7
SEISMIC ANALYSIS
e pea groun acce era on o a par cu ar s e epen s onthe following parameters.
Soil stratum
Distance from epicenter
.
IS 1893 defines PGA as
Sa Sa
0.1 0.30.4
2
G Gs sPGA =
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
8
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SEISMIC ANALYSISResponse SpectraSpectra Normalized to 1.0 Gravity (API RP 2A)
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
9
SEISMIC ANALYSIS
Response spectra for rock and soil sites for 5% damping (IS 1893)
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
10
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SEISMIC ANALYSIS
e o s o na ys s
Seismic co-efficient method
Time series method
Response spectra method
esponse cons era on
Horizontal acceleration both orthogonal directions
Vertical acceleration
Number of modes to be combined by complete quadraticcombination (CQC)
.(Square Root of Sum of Sequences)
e.g. ( ) ( ) ( )2 2 2
X Y ZER ER ER ER= + +
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
11
SEISMIC ANALYSIS
e sm c o-e c en me o
Design horizontal co-efficient
2h
ZISaA
Rg=
Where
Z =zone factor
I =importance factor
=average response acceleration co-efficient
R =response reduction factorg
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
12
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SEISMIC ANALYSIS
Total base shear can be calculated as
= .
Where
Ah=design horizontal seismic co-efficient
W=total weight of structure
Distribution of Design Forces
Design seismic force at each floor is to be calculated by
i ii B n
W hQ V=
1
j j
j
W h=
n=number of storage or points of mass located along the height.
14 June 2009Dr. S. Nallayarasu
Department of Ocean EngineeringIndian Institute of Technology
Madras-36
13
i=se sm c we g o oor,
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