1

“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

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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

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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

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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

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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

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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

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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

[17] M.A. Erberik, A.S. Elnashai, Fragility analysis of flat-slab structures’, Engineering

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a hybrid method of vulnerability assessment, Natural Hazards, 17(2), 1998, 177–92.

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[20] Mundra Port Development Authority, Detail Project Report of Mundra Port Development -

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Computers and Structures, Inc., Berkeley, CA, 2004.

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supported wharf, Soil Dynamics and Earthquake Engineering, 31, 2011, 830–840.

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Seismic criteria for California marine oil terminals : voulme-I, 1999, Long Beach, CA.

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of Gujarat, Natural hazards, 60( 2), 2012, 541-565.

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Seismic Hazard Map of India: Appendix II - Application of the PSHA Results. Govt. of

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