performance based design” dhara shah...resistant design standards is1893 part-1 [4] and is13920...
TRANSCRIPT
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“Fragility analysis of pile supported wharf using
Performance based design”
Synopsis of PhD. Thesis
Submitted to
Gujarat Technological University, Ahmedabad
for the Degree of
Doctor of Philosophy
in
Civil Engineering Branch
by
Ms. Dhara Shah
Enrollment No. 119997106003
2011 Batch
under supervision of
Prof. Dr. Bharat J. Shah
Applied Mechanics Department, LDCE, Ahmedabad
Co-supervisor
Dr. Beena Sukumaran
Rowan University, US
Professor and chair, Civil and Environment Engineering Department
Rowan University, New Jersey
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Contents
1. Abstract
2. Introduction / State of the art
3. Objective and scope of work
4. Literature review
5. Identification of research gap and Hypothesis
6. Problem formulation / Problem definition
7. Research methodology
8. Experiments/ Data collection/ Core Analysis
9. Deriving Seismic fragility curves for some important ports in Gujarat using CSM
a. Mundra port
b. Dahej port
c. Navlakhi port
d. Hazira port
e. Kandla port
10. Results and Discussions / Conclusions
11. Future scope
12. Validation
13. Publications with copies
14. References
3
1. Abstract
Maritime transportation has played a vital role in deciding economy of a country through
prehistoric times. Rapid development of international sea trade in the last few decades has drawn
attention towards seismic safety of port structures. A number of pile supported wharves have
suffered extensive damage due to seismic events in the past decade, causing extended economic
losses to port [1]. Currently in India, no guideline is available for seismic design of Port
structures and hence seismic vulnerability analysis of such structures becomes essential. Seismic
fragility analysis is a vital tool to comprehend structure’s performance and probability of failure
for different intensity of earthquakes. In the present study, seismic fragility curves are developed
for a typical pile supported wharf for some important port sites in Gujarat i.e. Mundra, Kandla,
Navlakhi, Dahej and Hazira, thereby representing very severe and moderate level of seismic
hazards (Zone V and III) as per IS1893 part-1:2002. Fragility curves are developed for three
levels of ground shaking i.e. Serviceability Earthquake (SE), Design Based Earthquake (DBE),
and Maximum Considered Earthquake (MCE). The structural model of wharf is prepared in SAP
2000 using Winkler model to represent soil pile system. Pushover analysis is performed to obtain
the capacity curve of wharf. Damage states are defined as per PIANC. Site specific spectra is
constructed using geotechnical report of port sites and related seismic events are selected,
normalized, and scaled from 0.1g to 1.0g, which represents demand. Using Capacity Spectrum
Method and linear Time History Analysis, maximum displacements at deck are obtained and
response matrix is created. Based on the damage states and the response matrix, the fragility
curves of the wharf are constructed.
It is observed that the selected port sites have much higher ground motions than specified by the
default spectrum of IS1893 part-1:2002. It is also revealed that the port sites Mundra, Kandla and
Navlakhi are most susceptible to seismic risk. Dahej and Hazira ports are comparatively at lower
risk. The Indian standard (IS1893 part-1:2002) thus underestimates the fragility of wharf at
selected sites, stating it to be functional for DBE and MCE. The site specific spectrum obtained
at selected sites clearly indicates the wharf as deficient in terms of serviceability during its
design life. Hence, site specific spectrum is necessary for seismic design of port structures. There
is also a need to review the exisitng Indian standard in context to ground motions.
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2. Introduction
Port transportation is one of the most important logistical systems, supporting universal
movement of passengers and cargos cost effectively, thereby acting as a backbone for economic
growth of country. A large numbers of important ports are located in active seismic regions
worldwide. Historical cases of seismic events in seaports have shown vulnerability of wharves to
threatening earthquakes including Loma Prieta in 1989, Kobe in 1995, Bhuj in 2001, Haiti in
2010, Tohoku in 2011 and others [2]. Although the probability of earthquakes is lower for port
structures, the risks of damage are greater, making seismic vulnerability assessment of such
structures an essential operation. Indian ports handle nearly 95% of foreign trade by volume and
70% by value [3]. About 65% of country’s land is under moderate to very high seismic risk and
the country has witnessed several major earthquakes in the past three decades. Currently, there is
no guideline in India for earthquake resistant design of port structures. The existing earthquake-
resistant design standards IS1893 part-1 [4] and IS13920 [5] are proposed for buildings that
behave very differently from port structures during earthquakes [6].
3. Objective and Scope of study
In the absence of specific seismic design code for port structures, it becomes necessary to make
vulnerability analysis of structure to understand its behavior and probability of failure (or
probability of repair work after seismic hazard) for different intensity earthquake. Hence seismic
fragility analysis of port structures becomes essential.
The ultimate objective of the study is to derive seismic fragility curves for a pile supported wharf,
for three different levels of earthquake motions, for some important port sites in Gujarat.
Scope of work
Preparing 3D model of pile supported wharf in SAP2000, analyzing it for various forces
acting on it as per IS4651 part-3 [7] and designing it for given load combinations as per
IS4651 part-4 [8].
Performing nonlinear static pushover analysis on the wharf to obtain its capacity curve
and identifying damage states as per PIANC.
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Constructing site specific spectra for three levels of earthquake motions, with reference to
IBC [9] and ASCE [10]; comparing it to the default spectra provided by IS1893 part-1.
Evaluating the seismic performance of wharf using Capacity Spectrum Method (CSM)
[11] and linear Time History Analysis.
Deriving seismic fragility curves for the selected wharf for three different levels of
earthquake motions, for some important port sites in Gujarat.
4. Literature review
From a structural point, fragility curve represents the probability that structural damage of a
structure, under various levels of seismic ground motions exceeds specified damage states.
Fragility curves can be related to ground motion or permanent ground displacement. The former
incorporates damage due to ground shaking. The latter incorporates damage due to the
permanent displacement, induced by ground failure such as liquefaction or landslide. Damage
states may be classified as serviceable, repairable, near collapse and collapse [2]. Many countries
have developed earthquake loss analysis systems such as Hazards U.S. – HAZUS [12] and
Taiwan Earthquake Loss Estimation System – TELES [13]. These systems use fragility curves to
estimate the damage probabilities of the components in a system.
Fragility curves can be classified as empirical, judgmental, analytical and hybrid. Empirical
fragility curves use damage data from past earthquakes, being the most realistic approach and
situation specific [14]. Judgmental fragility curves use expert opinion such as in ATC13 [15] and
HAZUS. However, its reliability depends on the experience of experts consulted and nature of
subsequent relations [16]. Analytical fragility curves use numerical analysis as base, wherein
structural models are analyzed for damage responses under increasing earthquake intensity.
Extensive analyses make them reliable for vulnerability assessment of different structures
compared to the other two methods [17]. Hybrid fragility curves are based on a combination of
all three methods [18].
5. Identification of the research gaps based on literature review
Very few guidelines are available for the seismic design of port structures around the world. In
1997, International Navigation Association formed a working group - PIANC and published a
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document ‘Seismic Design Guidelines for Port Structures’, which focused international attention
on destruction of earthquakes on port facilities and introduced the concept of performance based
seismic design of port structures. PIANC states that most failures of port structures result from
excessive deformations and soil structure interaction. Hence, the design methods based on
displacements and ultimate stress states are desirable over conventional force-based design
methods for defining the comprehensive seismic performance of port structures.
Fragility analysis helps in improving the performance of a structure by estimating its repair cost
and operational status. The repair cost is the cost of retrofitting involved in bringing back the
capacity of a structure to its original (pre-earthquake) condition. The operational status of a
structure is either operational or non-operational. Many countries have already developed
earthquake loss analysis systems.
Hypothesis
The derived fragility curves provide an insight to the decision makers to capitalize on
investment for wharf retrofit and fill a major gap in seismic vulnerability assessment of ports,
which can be used to evaluate the socio economic impact of the damage to wharves during a
natural hazard event.
6. Problem formulation
A typical pile supported wharf at Mundra port, Gujarat (Latitude: 22º 43’ 88” N; Longitude: 69º
42’ 34” E) is selected for the study. The site is an ideal deep water port and the largest private
port in India with an advantage of proximity to international sea routes. The site lies in highest
seismic risk zone - zone V, with Maximum Considered Earthquake (MCE) as 0.36g and Design
Base Earthquake (DBE) as 0.18g as per IS1893 part-1. The site is located at approx. 50 km from
Katrol Hill Fault (KHF), one of the active faults in the region. Most faults located in this region
have reverse / reverse oblique mechanism, capable of generating earthquakes of magnitude 6-8
[19]. Selected wharf is 585.5m long with 50mm expansion joint provided at every 58.5m, 48.5m
wide, housing 150000 DWT container vessels. The wharf is constructed with precast / in-situ
RCC beams with 0.5m thick deck supported on 45 bored cast in-situ piles. Pile spacing is 6.5m
in longitudinal direction and 11.2m & 7.6m in transverse direction. Selected wharf unit is 58.5 m
long and 48.5 m wide. Maximum and minimum recorded tidal levels are + 6.4m and 0.0m. M40
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grade of concrete and Fe500 grade of steel reinforcement is used. Table 1 lists the pile summary
[20]. The wharf layout and profile is shown in Fig. 1 and Fig. 2.
TABLE 1: Pile summary
Pile
Type
Diameter
(m)
Longitudinal reinforcement Transverse reinforcement Helical
Grid A 1.3 34 – 32 mm Dia. 12 mm Dia. @ 250mm pitch
Grid B 1.0 20 - 32 mm Dia. 12 mm Dia. @ 250mm pitch
Grid C 1.0 10–32 mm Dia.+10-25 mm Dia. 12 mm Dia. @ 250mm pitch
Grid D 1.2 32 - 32 Dia. 12 mm Dia. @ 250mm pitch
Grid E 1.2 16-32 mm Dia. + 8–25 mm Dia. 12 mm Dia. @ 250mm pitch
FIGURE 1: Typical layout of the selected wharf
1
2
3
4
5
6
7
8
9
2800 11200 7600 11200 11200 4500
6500
6500
6500
6500
6500
6500
6500
3250
SLAB PANEL LAYOUT
30000
A B C D E
A B C D E
1
2
3
4
5
6
7
8
9
6500
3250
8
FIGURE 2: Typical profile of the selected wharf
7. Research methodology
Numerical model
SAP 2000 is used to prepare 3D model (frame structure) of the wharf [21]. As RC beams are
partly precast and partly cast in-situ, rigid diaphragm action due to deck is not considered. Piles
are modeled by beam elements, rigidly connected to the deck. Winkler model is used to represent
soil pile system. Linear springs have been used for the present study. Springs are distributed
along the length of pile by Newmark’s distribution. Time period of the structure as per IS1893
part-1 formula is 0.87s. (structure without infills). Mander concrete model and simple bilinear
steel model are used in the present study.
Method of analysis for pile supported wharf
PIANC recommends four methods of analysis, viz. methods A, B, C and D. Method A is a
simplified analysis wherein the wharf behaves as a structure with a single degree of freedom
under transverse response. Method B is multi-mode spectral analysis, where several piles in a
line are lumped as a stand-alone element. This method is used in conjugation with pushover
analysis. Method A and B are simplified analysis methods, used for preliminary design. Method
C is Nonlinear Static Pushover Analysis and method D is Time History Analysis wherein
A B C D E
11200 7600 11200 11200
8.5 m DECK LEVEL
6.185 m
3.795 m
1.500 m
4
1
1.83
1
ROCKFILL LINE
DREDGE LINE
-44.000 M
FDG LVL
-20.000 M
FDG LVL
1300Ø BOREDCAST-IN-SITU PILE
1000Ø BOREDCAST-IN-SITU PILE
1000Ø BOREDCAST-IN-SITU PILE
1200Ø BOREDCAST-IN-SITU PILE
1200Ø BOREDCAST-IN-SITU PILE
BUILTUP COLUMN
2000
660010200
600
1000
1500
1000
2100
500300 200
(-)17.800mDREDGED LEVEL
7000
(-)18.800m
17400
SCOUR PROTECTION APRON
3400
10100
10000 9800
2500 2500 2500 2500 1000 2200 2200 2200 1000 2500 2500 2500 2500 1400 2450 2450 2450 2450 1400 38001400
0.000 mLAT
9
different real time recorded accelerations along with soil-structure interactions are used to get
structural response. For the present study, method C and D are adopted. Owing to time constraint
and inaccessibility to high speed computer, instead of nonlinear time history analysis, linear time
history analysis is chosen. However, preliminary analyses using methods A and B are performed
to verify the results.
8. Experiments/ Data collection/ Core Analysis
Pushover analysis and damage state definition
To perform pushover analysis, hinges are assigned along the pile length and to the beam.
PM2M3 hinges are assigned in piles and M3 hinges in beams [11]. Pushover analysis is
performed to obtain the capacity curve of the wharf. Prior, modal analysis is performed to get the
fundamental modal shape of the wharf. The fundamental time period of the wharf is 1.35s. The
wharf moves along x direction (towards land). The displacement is examined at deck pile
junction. It is observed that grid E piles are critical, with axial load carrying capacity in the range
of 0 kN to 4000 kN. Figure 3 shows the moment curvature curves for Grid E piles, calculated
using section designer module of SAP 2000.
FIGURE 3: Moment curvature plot for grid E Pile
PIANC recommends qualitative criteria to judge the damage states of pile supported wharf,
based on peak pile response as shown in Table 2. There are four damage states i.e. I, II, III and
IV, related to serviceable, repairable, near collapse and collapse levels of a wharf structure. At
serviceable level, the structure continues to function with minor or no structural damage. At
repairable level, the structural damage is controllable and repairable. At near-collapse level, the
0
1000
2000
3000
4000
5000
6000
0 0.01 0.02 0.03 0.04
Mo
men
t (k
Nm
)
Curvature (1/m)
P = 0 kN
P = 2000 kN
P = 4000 kN
10
structural damage is substantial. At collapse level, the structural strength is completely lost.
Hence upper bounds of the damage states I, II and III are based on the sequence of plasticity
development during the pushover process highlighted by the points Cd, Yd and Ud on the capacity
curve as shown in Fig. 4. Cd is the state where a pile initially cracks below water. Yd is the state
where a pile yields below water. Ud is the state where a pile section reaches its ultimate state
below water [22]. In any case, pile section below water is very critical as crack formed in pile
below sea water will gradually expand and cause corrosion thereby affecting the serviceability of
the wharf, making investigation and repair work rigorous, and the section eventually fails.
Accordingly, the damage bounds selected from the capacity curve for damage states I, II and III
are 83 mm, 261 mm and 505 mm.
PIANC specifies two levels of earthquake motions i.e. Level I (L1) and Level II (L2), to be used
as design reference. L1 is Serviceability Earthquake i.e. SE, having 50% probability of being
exceeded in 50 years with a return period of 72 years. L2 is Design Based Earthquake i.e. DBE,
having 10% probability of being exceeded in 50 years with a return period of 475 years. A
number of wharf design guidelines suggest the use of additional level of earthquake motion i.e.
Level III – L3 having probability of exceedance as 2%, with a return period of 2475 years for a
50 year life span of structure, known as Maximum Considered Earthquake – MCE. This level
pertains to ports handling oil terminals, container terminals and hazardous materials. From the
design earthquake levels and accepted damage levels, performance of wharf is quantified.
TABLE 2: Accepted level of damage in performance based design and pile peak response [2]
Accepted level of damage
Damage type Degree I
(Serviceable)
Degree II
(Repairable)
Degree III
(Near Collapse)
Degree IV
(Collapse)
Structural General Minor or no damage Controlled damage Extensive damage
in near collapse
Complete loss
of structure
Pile peak
response
Essentially elastic
response with minor
or no residual
deformation
Controlled limited
inelastic ductile
response and residual
deformation
intending to keep the
structure repairable
Ductile response
near collapse
(double plastic
hinges may occur
at one or limited
number of piles)
Beyond the
State III
Operational Little or no loss of
serviceability
Short term loss of
serviceability
Long term or
complete loss of
serviceability
Complete loss
of
serviceability
11
FIGURE 4: Capacity curve of the wharf structure with displacement bounds
Time history analysis and damage state definition
As per PIANC, the moment curvature curves derived for grid E piles can be idealized to get
damage bounds. The axial forces, corresponding moments and curvatures for different limit
states are calculated. Calculations of displacement bounds require plastic hinge length of pile and
plastic rotation capacity of plastic hinge as per PIANC. Damage bounds derived for damage state
I, II and III are 102 mm, 445 mm and 787 mm. Similarly damage bounds are derived for method
A and B [23]. Table 3 shows damage bounds derived for all methods.
TABLE 3: Displacement bounds derived from different methods
Analysis type Damage state
I II III
Method A – Simplified analysis 0.098 m 0.327 m 0.490 m
Method B – Multi mode spectral analysis 0.050 m 0.163 m 0.245 m
Method C – Pushover analysis (reliable) 0.083 m 0.261 m 0.505 m
Method D – Linear Time history analysis 0.102 m 0.445 m 0.787 m
Site specific spectra and ground motions
As per the soil report, the selected site has an average shear wave velocity of 200 - 300 m/s,
for top 30 m of soil [24]. Such soil is normally classified as type D as per IBC [9] and ASCE
[10]. ATC40 and PSHA report of National Disaster Management Authority [25] recommends
0
5000
10000
15000
20000
25000
30000
35000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Ba
se F
orc
e (k
N)
Roof Displacement (m)
Pushover Curve
a pile initially cracks at the
top
a pile initially cracks below
the water
a pile yields at the top
a pile yields below the water
a pile reaches its ultimate
state at the top
Cd
Yd
Ud
12
site specific hazard analysis for such soil type, for three levels of earthquakes i.e. L1, L2, and
L3. The site-specific spectra obtained for L1, L2 and L3 earthquakes for the selected site are
shown in Fig. 5.
FIGURE 5: Site Specific Spectra for Mundra port site, Gujarat
Owing to the absence of past earthquake records for the selected site, five pairs of earthquake
events (10 events) were obtained from the PEER ground motion database website [26], having
similar topographical features, soil conditions, magnitude, fault type, and distance from source of
earthquake.
Wharf response and fragility analysis
For method C, Capacity Spectrum Method (CSM) is used to obtain the response of wharf. The
wharf is classified as Type B as per ATC40 hysteresis damping model. Ground motions are
transformed into demand spectrum and the capacity curve of wharf is transformed into capacity
spectrum. Seismic response of wharf is obtained in terms of displacement. For method D,
accelerograms of selected earthquake records are used to obtain wharf response. It is observed
that CSM is more reliable over other methods and hence CSM is used to derive fragility curves
of all considered port sites. For fragility analysis, intensity measure is represented in the form of
PGA. The selected earthquake events are normalized and scaled from 0.1g to 1.0g to get a
response matrix. The fragility curves derived are shown in Fig. 6. Table 5 shows probability of
failure of wharf under all levels of earthquake motions.
0
0.5
1
1.5
2
2.5
3
3.5
0.0 2.0 4.0 6.0 8.0 10.0
Sp
ectr
al
acc
eler
ati
on
(g
)
Time (s)
Level I - L1 = 0.294g
Level II - L2 = 0.883g
Level III - L3 = 1.325g
13
FIGURE 6: Simplified lognormal fragility Curves for Mundra site using CSM (250mm pitch)
TABLE 4: Probability of failure of selected wharf under all seismic levels
Probability of failure
EQ Level Analysis type Repairable Near Collapse Collapse
L1 (SE) CSM 90% 1% 0%
Time History 100% 6% 0%
L2 (DBE) CSM 100% 90% 39%
Time History 100% 96% 50%
L3 (MCE) CSM 100% 100% 99%
Time History 100% 100% 100%
9. Seismic fragility curves for some important port sites in Gujarat using CSM
Apart from Mundra port, seismic fragility curves are also derived for few other important
port sites in Gujarat. The configuration of pile supported wharf model has been kept same as
in previous case. The ports taken under study are:
Dahej
Navlakhi
Hazira
Kandla
Figure 7 shows the location of ports under study on Gujarat map. Geotechnical data of the
selected port sites is obtained from Gujarat Maritime Board. Seismic fragility curves are
derived for the said port sites using CSM are shown in Fig. 8, Fig. 9, Fig. 10 and Fig. 11.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Pro
bab
ilit
y o
f fa
ilu
re
PGA (g)
Damage state I
Damage state II
Damage state III
EQ L1
EQ L2
EQ L3
I
II
III
IV
L1 L2 L3
14
FIGURE 7: Gujarat map showing location of ports under study; source: www. wikimapia.org
Dahej (Zone III as per IS1893 part-1:2002)
Dahej port is located in the Gulf of Cambay, Gujarat. It is a natural deep water port on the
west coast of India (Latitude: 21º 70’ N; Longitude: 72º 53’ E). Selected site lies in
earthquake zone III as per IS1893 part-1. PGA values for EQL1, EQL2 and EQL3 are
0.054g, 0.163g and 0.245g.
FIGURE 8: Simplified lognormal fragility Curves for Dahej port site
Navlakhi (Zone V as per IS1893 part- 1: 2002)
Navlakhi port is located at inner position of the Gulf of Kutch on the west coast of India
(Latitude: 22º 58’ 25” N; Longitude: 70º 27’24” E). It is an all-weather lighterage working
port. Selected site lies in earthquake zone V as per IS1893 part-1. PGA values for EQL1, EQL2
and EQL3 are 0.272g, 0.817g and 1.226g.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Pro
ba
bil
ity
of
fail
ure
PGA (g)
Damage state I
Damage state II
Damage state III
EQ L1
EQ L2
EQ L3
I
II
III
IV
L1 L2 L3
15
FIGURE 9: Simplified lognormal fragility Curves for Navlakhi port site
Hazira (Zone III as per IS1893 part -1: 2002)
Hazira (Surat) port is strategically located in the Gulf of Cambay, Gujarat (Latitude: 21º 06’ N;
Longitude: 72º 37’ E). Selected site lies in earthquake zone III as per IS1893 part-1. PGA values for
EQL1, EQL2 and EQL3 are 0.072g, 0.217g and 0.325g.
FIGURE 10: Simplified lognormal fragility Curves for Hazira port site
Kandla (Zone V as per IS1893 part -1: 2002)
Kandla port is one of the major port of India, located in the Kandla creek on the west coast of India
(Latitude: 23º 01’ N; Longitude: 70º 13’ E). It is a protected natural harbor. Selected site lies in
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
Pro
ba
bil
ity
of
fail
ure
PGA (g)
Damage state I
Damage state II
Damage state III
EQ L1
EQ L2
EQ L3
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Pro
ba
bil
ity
of
fail
ure
PGA (g)
Damage state I
Damage state II
Damage state III
EQ L1
EQ L2
EQ L3
I
II
III
IV
L1 L2 L3
I
II
III
IV
L1 L2 L3
16
earthquake zone V as per IS1893 part-1. PGA values for EQL1, EQL2 and EQL3 are 0.165g, 0.495g
and 0.743g.
FIGURE 11: Simplified lognormal fragility Curves for Kandla port site
10. Results and Discussions
Variation in fundamental time period of the wharf using Modal analysis and IS1893
part -1:2002 formula.
According to IS1893 part-1:2002 the approximate fundamental natural period of
vibration (Ta), in seconds, of a moment resisting frame building without brick infill
panels may be estimated by the empirical expression:
𝑇𝑎 = 0.075h0.75, for RC frame building, where ‘h’ is the height of building in m. Hence,
Ta = 0.87s. But, from the dynamic mode shape analysis, T = 1.35s. Hence variation in
time period of the wharf is around 35% with respect to modal analysis which greatly over
estimates the seismic forces.
**In the absence of specific seismic design code for port structures, IS1893 part-1:2002
is used in the present study to predict seismic forces acting on the wharf. Hence the
formula for computing time period of the structure is taken as per IS1893 part-1:2002.
Variation in bending moment values in piles using pile fixity depth approach and soil
spring constant approach…specifically grid E pile.
Variation in bending moment values in piles, specifically grid E piles, is observed using
pile fixity depth and soil spring constant approach due to change in the fundamental time
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Pro
ba
bil
ity
of
fail
ure
PGA (g)
Damage state I
Damage state II
Damage state III
EQ L1
EQ L2
EQ L3
I
II
III
IV L1 L2 L3
17
period of the structure and the corresponding base shear values. Table 5 below shows the
difference.
Thus, pile fixity depth analysis over estimates the design forces.
TABLE 5: Variation in bending moment values in piles
Pile Grid Diameter (m) Bending Moment
Mfixity
(kNm)
Bending Moment
Mspring
(kNm)
Variations w.r.t
Mspring
(%)
Grid A 1.3 3359.22 3059.50 10
Grid B 1.0 2177.18 1123 94
Grid C 1.0 3017.59 1431 111
Grid D 1.2 9643.41 4995.5 93
Grid E 1.2 12248.74 4119 197
Extreme variation in PGA values as per site specific spectra and the default spectra
provided by IS1893 part-1:2002.
As per IS1893 part-1, PGA values for MCE and DBE in zone V is 0.36g and 0.18g
whereas the PGA values obtained using site specific spectra for Mundra, Navlakhi and
Kandla port sites (zone v) for MCE are 1.325g, 1.226g and 0.743g. Similarly, PGA
values obtained for DBE are 0.883g, 0.817g and 0.495g. Variation in PGA values for
these port sites is observed in range of 100% – 268% with respect to IS1893 part-1 for
MCE and 175% – 390% for DBE.
Similarly, as per IS1893 part-1, PGA values for MCE and DBE in zone III is 0.16g and
0.08g. The PGA values obtained using site specific spectra for Hazira and Dahej port
sites (zone III) for MCE are 0.325g and 0.245g whereas for DBE are 0.217g and 0.163g
respectively. Variation in ground motion values for these port sites is observed in range
of 53% – 103% with respect to IS1893part-1 for MCE and 103% – 171% for DBE.
Hence, IS1893 part-1 underestimates the ground motions in zone V and zone III.
18
Probability of failure of wharf at all ports under all seismic levels (CSM)
TABLE 6: Probability of failure of wharf at all ports under all seismic levels (CSM)
Probability of failure
EQ Level Port site Repairable Near Collapse Collapse
L1 (SE) Dahej 3% 0% 0%
Hazira 6% 0% 0%
Navlakhi 30% 1% 0%
Kandla 52% 0.1% 0%
Mundra 90% 1% 0%
L2 (DBE) Dahej 22% 1% 0%
Hazira 35% 1.5% 0%
Navlakhi 88% 22% 3%
Kandla 100% 82% 24%
Mundra 100% 75% 18%
L3 (MCE) Dahej 42% 2% 0.1%
Hazira 58% 5% 0.3%
Navlakhi 99% 44% 9%
Kandla 100% 99.5% 83%
Mundra 100% 100% 70%
It is observed that the Mundra, Navlakhi and Kandla port sites are vulnerable to seismic
threat with probable DBE in order of 0.883g, 0.817g and 0.495g. Hazira and Dahej port sites
have comparatively less seismic threat with probable DBE of 0.217g and 0.163g
respectively. The wharf structure under Mundra, Kandla and Navlakhi port sites happens to
be in deficient mode, with probability of entering repairable state as 88%, 100% and 100%
for DBE. The probability is 100% for MCE for all three ports. The wharf structure under
Dahej and Hazira port sites remains intact, with probability of entering repairable state as
22% and 35% for DBE. The probability increases to 42% and 58% for MCE.
Conclusions
IS1893 part-1:2002 underestimates the seismic ground motions at selected port sites.
As observed, IS1893 part-1 underestimates ground motions at selected port sites. Hence
there is a strong need to revise our existing standards, providing guidelines for seismic
design of port structures.
A Site specific spectrum is essential for seismic design of port structures.
Mundra, Kandla and Navlakhi ports lie in same seismic zone - V as per Indian standard.
19
Similarly, Dahej and Hazira port do lie in same seismic zone – III. Although port sites
are in same seismic zone, each site has distinct soil profile and seismic threats, thereby
imparting variation in the ground motions.
Socio economic aspect
Seismic damage to port structures result in direct and indirect losses. Direct losses deal
with the costs of retrofitting or replacement to the damaged port component. Indirect
losses are economic losses associated with loss of serviceability of port i.e. trade
interruption, investment, etc. Magnitude of indirect losses will depend on the extent of
damage to port structure. Past experiences also reveal that indirect losses due to
earthquake damage can far exceed the direct losses.
Hence, it is felt that all significant raw commodities imported to India through Mundra,
Kandla and Navlakhi ports might be shifted to Dahej and Hazira ports so as to avoid
disruption of supply of materials during seismic events.
11. Further Scope of Research
In the present study, linear soil pile interaction model is considered. Finite Element Model
may be used to predict more realistic behavior of soil during predetermined seismic event.
In present study Capacity spectrum method (Nonlinear static) is used to derive the response
matrix (conventional approach). To obtain more detailed result, Dynamic analysis (Nonlinear
Time History Analysis) may also be used.
In this study, Seismic Fragility Curves have been constructed assuming that no lateral force
other than earthquake is acting at the same time. However, for more realistic study, various
combinations of load may be considered.
Structural health monitoring of piles by Non Destructive Testing can also be done, which is
not a part of this study.
Site specific spectra obtained using ASCE 7/05 approach can be compared with SHAKE
analysis to see how similar or different they are.
12. Validation
To validate the research work, seismic fragility analysis of an existing residential building
located at commerce six roads, Ahmedabad, Gujarat has been carried out. The building was
designed and constructed in 1970 and has already faced Bhuj 2001 earthquake. Building plan is
20
regular. Vertical irregularity is present in the building as one of its sides is G+2 storey whereas
the other side is G+3 storey. Figure 12 shows the structural system of the building. Soft story is
present in half plan of the building. Area of the building is 2500 square-ft/ floor. Columns in the
stair block were under short column effect and retrofitting was done on those columns post Bhuj
earthquake 2001. Also majority of peripheral columns were retrofitted post-earthquake as shown
in Fig. 13. Many separation cracks near column and walls were also observed.
FIGURE 12: Structural system of building
FIGURE 13: Retrofitted peripheral columns
21
SAP2000 is used to prepare 3D model of Suparna flats. The technical properties of the building
as obtained from the consultant are given in Table 7. The design spectrum used for the building is as
per the default spectrum provided by IS1893 part-1 [4] for medium soil and the building site falls under
seismic zone III. Due to lack of availability of past earthquake records for the selected site,7 earthquake
records are obtained from PEER ground motion database website [26]. Derived fragility curves for the
selected building are shown in Fig. 14. Table 8 shows the probability of failure of building for different
earthquake levels.
TABLE 7: Relevant technical properties of the building
Column size : 230 mm x 400 mm
Beam size : 230 x 450 mm
Slab thickness : 125 mm
Concrete grade : M20
Reinforcement : Fe415
Storey height : 3 m
Depth of foundation : 2 m
Soil type : Yellow Murrum
SBC : 180 kN/m2
N value of soil : 17 - 20
FIGURE 14 : Fragility curves for the selected building
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Pro
ba
bil
ity
of
fail
ure
PGA (g)
Damage state I
Damage state II
Damage state III
EQ L2 - 0.08g
EQ L3- 0.16g
Bhuj EQ - 0.11g
I
II
III
IV
L2 L3
22
TABLE 8: Probability of failure of building under given seismic levels
Probability of failure %
EQ Level Repairable Near Collapse Collapse
L2 (0.08g) 47% 4% 0%
L3 (0.16g) 84% 49% 4%
Bhuj EQ(0.11g) 63% 12% 0%
From the above table, the probability of building entering in repairable zone for Bhuj earthquake
is 63%. The probability of entering near collapse and collapse state is 49% and 4% respectively.
The building has faced Bhuj earthquake 2001 and undergone retrofitting in 23 columns out of 38
columns. The building is still in use. It can be understood that the analysis results are in fair
range.
13. Publications
A paper title “Performance based seismic design of port structures: state of art” published
and presented at Structural Engineering Convention 2012 (SEC 2012), held at SVNIT
Surat, 19-21 December 2012.
A paper title “Seismic fragility analysis of pile supported wharf: state of art” published and
presented at Structural Engineering Convention 2014 (SEC 2014), held at IIT Delhi, 23-
25 December 2014.
A paper title “Seismic fragility analysis of pile supported wharf using linear time history
analysis” has been accepted in Journal of Structural Engineering JOSE (SERC,
Chennai).
A paper title “Comparative study of seismic fragility curves for a pile supported wharf using
capacity spectrum method and time history analysis” has been accepted in International
Journal of Earthquake Engineering and Hazard Mitigation (IREHM).
A paper title “Seismic fragility analysis of pile supported wharf for some important port sites
in Gujarat” under review in International journal “Soil Dynamics and Earthquake
Engineering”, Elsevier Editorial System TM.
A paper title “Seismic Fragility Analysis of Pile Supported Wharf Using Capacity Spectrum
Method” under review in Journal of Seismology and Earthquakes Engineering (JSEE).
23
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24
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