Lateral Strength and Safety Evaluation of Piers of ... · PDF fileFinally, safety of the piers...

International Journal of

Advanced Structures and Geotechnical Engineering

ISSN 2319-5347, Vol. 06, No. 02, April 2017

IJASGE 060201 Copyright © 2017 BASHA RESEARCH CENTRE. All rights reserved

Lateral Strength and Safety Evaluation of Piers of Kadamtali Flyover

in Chittagong, Bangladesh

MOHAMMAD RAIHAN MUKHLIS1*

MD. ABDUR RAHMAN BHUIYAN2

1Institute of Earthquake Engineering Research, Chittagong University of Engg. and Tech, Bangladesh

2Department of Civil Engineering, Chittagong University of Engg. and Tech, Bangladesh

Email: [email protected]

Abstract: Chittagong, the only sea port city of Bangladesh, situated in seismically active region near

Chittagong-Tripura Fold Belt (CTFB) may experience certain strong earthquakes resulting severe damage of

existing bridges like Kadamtali flyover. The current study mainly aims at safety evaluation of piers of

Kadamtali flyover. To the end, failure mode, lateral strength and displacement ductility of piers have been

evaluated as recommended by Japan Road Association (JRA). Ultimate flexural strength of piers has been

computed from the force-displacement relationships obtained by the moment curvature relationships of piers as

per JRA and using SeismoStruct. Moment curvature relationships of piers are derived from nonlinear sectional

analysis of pier sections. Shear capacity of piers have been calculated by the equations provided by JRA. Lateral

strengths have been determined depending on the three failure mode of the piers where displacement ductility

have been computed using yield and ultimate displacement of flyover piers obtained from the force-

displacement relationships. Three spectral accelerations corresponding to three peak ground accelerations

(PGA) related to the seismic zoning of Bangladesh are used in safety evaluation. Lateral force demand of piers

corresponding to spectral acceleration is determined using the displacement ductility and seismic weight.

Finally, safety of the piers is evaluated according to ductility design method described by JRA.

Keywords: Flyover; Failure Mode; Lateral Strength; Displacement Ductility; Pushover Analysis; Safety

Evaluation.

Introduction:

Flyovers are generally those bridges which are

constructed at intersections of highways that cross

over another road to separate the vehicles of different

direction and to form a grade separation. In recent

years, flyovers have become the easiest alternative to

compensate traffic jams at intersections of major

cities in Bangladesh. A number of flyovers are being

constructed in Dhaka and Chittagong metropolitan

cities with a view to reducing the traffic

congestions.Bridge structure plays very important

role for evacuation and emergency routes for rescues,

first aid, medical services, fire-fighting and

transporting urgent disaster commodities (Alim et.

al., 2014). Highway bridges are vulnerable to

earthquakes proved by past earthquakes, such as the

1971 San Fernando earthquake, the 1994 Northridge

earthquake, the 1995 Great Hanshin earthquake in

Japan, and the 1999 Chi-Chi earthquake in Taiwan

(Hwang et. al., 2001). A number of highway bridges

have collapsed or have been severely damaged by

some previous earthquakes, even though they were

subjected to earthquake ground shaking of an

intensity that has been frequently less than the current

code intensities (Khan et. al., 2014).When the rocks

along a weak region in the earth’s crust reach their

strength, a sudden movement takes place and

opposite sides of the fault suddenly slips and release

the large elastic strain energy stored in the interface

rocks. The sudden slip at the fault causes the

earthquake. A violent shaking of the earth when large

elastic strain energy released spreads out through

seismic waves that travels through the body along the

surface of the earth. Most earthquakes in the world

occur along the boundaries of the tectonic plates

(UPSeis, 2016). By its geographical position,

Bangladesh is being treated as very vulnerable

country with its high risk of earthquake hazard. The

Indian plate is moving 60 mm/yr in a northeast

direction and subducting at the rate of 45 mm/yr

under the Eurasian and 35 mm/yr under the Burmese

plates in the north and east, respectively (Bilham,

2004). Bangladesh stands on the northeastern corner

of the Indian plate while Chittagong is situated over

Chittagong-Tripura Fold Belt (CTFB). Most of the

active faults within CTFB is thought to be secondary

faults and deformations related to the rupture of the

Tripura segment shown in Fig. 1. However, a part of

these faults may generate large earthquakes

separately from the plate boundary fault like the 1918

Srimongal earthquake. However, it is difficult to

separate active structures from the secondary

structures. Some active faults within Chittagong have

been shown in Fig. 2 among which Sitakund fault,

Patia fault, Sitapahar fault, Kalabunia fault have

potentials to produce some significant earthquakes.

Sitakund fault zone is located at Northwest side of

Chittagong city and the nearest fault from main city

(Mukhlis et. al., 2016).

MOHAMMAD RAIHAN MUKHLIS, MD. ABDUR RAHMAN BHUIYAN

International Journal of Advanced Structures and Geotechnical Engineering

ISSN 2319-5347, Vol. 06, No. 02, April 2017, pp 45-56

Fig. 1: Active faults in and around Bangladesh

(Morino et. al., 2013)

Fig. 2: Active faults in and around Chittagong

(Alam, 2011)

In the seismic zoning map of Bangladesh, provided

in BNBC (Bangladesh National Building Code),

Chittagong has been shown under Zone II with basic

seismic zone coefficient of 0.15. But recent repeated

study reveals shocking value around this region

indicating the possibilities of potential threat of even

much higher PGA like 0.28g than projected, which

has already been proposed in BNBC draft 2012 as for

Chittagong under Zone III with basic seismic zone

coefficient of 0.28 (Al-Hussaini et. al., 2012). Since

bridges are one of the most critical components of

highway systems, it is necessary to evaluate the

seismic vulnerability of highway bridges in order to

assess economic losses caused by damage to highway

systems in the event of an earthquake (Hwang et. al.,

2001). Seismic vulnerability can be assessed in two

ways: empirically and analytically. Empirical

vulnerability analyses are virtually impossible for

Bangladesh, since structural damage data due to

earthquakes are not available. Hence, analytical

vulnerability analysis is an effective way to employ

for evaluating vulnerability of bridge structures.

Several seismic codes and standards, such as JRA,

2002; CalTrans, 1999; Euro Code, 1998; ASHTO,

1998; have been developed to evaluate seismic safety

of bridge structures. The main philosophy lied in

seismic safety evaluation that the structures shall

resist earthquakes of small to moderate magnitudes

without damage while for the large magnitude

earthquake excitations the reparability and no

collapse condition of the structures shall be ensured.

In this case, the structures are allowed to undergo

large deformations showing nonlinear behaviour and

energy dissipation for minimizing the losses (Khan

et. al., 2014). Based on the above background, the

study aims at evaluating the failure mode, lateral

strength, displacement ductility and safety status of

piers of the Kadamtali flyover. The guidelines

recommended by JRA, 2002 are used for this

purpose. The nonlinear static pushover analysis

method has been adopted to obtain the lateral

strength, yield and ultimate displacement of piers.

The lateral strengths and ductility of piers are

obtained by considering their flexural strengths, shear

strengths and failure modes. The flexural strengths

are obtained from sectional analysis results, while the

shear strengths are estimated by using code defined

equations. Finally, the seismic safety of piers of the

Kadamtali flyover has been evaluated for design

earthquake ground motion records as per BNBC.

Modeling Of the Flyover Bridge:

Kadamtali Flyover Bridge has been constructed in

December 2015 with a view to providing smooth

corridor for the traffic coming towards New Market

circle, the old centre of Chittagong city and

Chittagong railway station, from the entrance of the

town Alongkar Circle using another flyover at

Dewanhat Circle. The flyover is approximately 1127

m long and 8.54 m wide including two approach

roads with 320 m long towards Dewanhat and 177 m

long towards New Market. It is spaning around 630

m with 22 spans of variable length. The span length

of the bridge varies from 21.3 m to 42.0 m. There are

21 piers with variable height ranging from 4.66 m to

8.5 m in the flyover excluding two abutments at the

end. The 3-D view of Kadamtali Flyover and the

flyover after construction is shown in Fig. 3 and

Fig.4respectively.

Lateral Strength and Safety Evaluation of Piers of Kadamtali Flyover in Chittagong, Bangladesh



Fig. 3: 3-D view of Kadamtali Flyover

(Photo Courtesy: Premier Cement)

Fig. 4: Kadamtali Flyover after construction

(Photo Courtesy: Premier Cement)

The deck of the flyover comprises four pre-stressed

concrete girders with 200 mm reinforced concrete

slab in the straight portions and three consecutive box

girders at both of the two curved portion of the

flyover. The girders rest on elastomeric neoprene

bearing over concrete bearing pad installed on top of

each pier and abutment. Geometric dimensions of

piers and relevant material properties of the flyover

are presented in Table 1 and Table 2 respectively.

Table 1: Geometric Dimensions of Piers of Kadamtali Flyover

Pier

No.

Pier

height,

H (m)

Pier

Dimension

(mm x mm)

Longitudinal

Reinforcement

Pier

No.

Pier

height,

H (m)

Pier

Dimension

(mm x mm)

Longitudinal

Reinforcement

1 5.83 1200 x 2500 66-Y25 bar

12 7.97 1200 x 2500 66-Y25 bar

2 6.48 1200 x 2500 66-Y25 bar 13 7.17 1200 x 2500 66-Y25 bar

3 7.14 1200 x 2500 66-Y25 bar 14 6.52 1200 x 2500 66-Y25 bar

4 7.28 1200 x 2500 66-Y25 bar 15 6.32 1200 x 2500 66-Y25 bar

5 8.17 1200 x 2500 66-Y25 bar 16 6.49 1200 x 2500 66-Y25 bar

6 8.01 1200 x 2500 66-Y25 bar 17 6.07 1200 x 2500 66-Y25 bar

7 8.27 1200 x 2500 66-Y25 bar 18 6.36 1200 x 2500 66-Y25 bar

8 8.50 1500 x 3000 78-Y25 bar 19 5.56 1200 x 2500 66-Y25 bar

9 8.50 1500 x 3000 78-Y25 bar 20 5.65 1200 x 2500 66-Y25 bar

10 8.50 1200 x 2500 66-Y25 bar 21 4.66 1200 x 2500 66-Y25 bar

11 8.50 1200 x 2500 66-Y25 bar

Table 2: Material Properties of Piers of Kadamtali Flyover

Material Name Description of material properties

Reinforcement M. S. Deformed bar

Yield Strength, fy = 413 N/mm2

Concrete 28 days cylinder crushing strength, fc = 30 N/mm

2

Modulus of Elasticity, Ec = 2.5743E+010 N/mm2

Analytical Model

The superstructure & substructure of the system are

modelled as a lumped mass system divided into a

number of small discrete segments forming frame

elements. The analytical model of pier-girder system

is approximated as a continuous 2-D finite element

frame using the numerically solved nonlinear

analysis program (Khan et. al., 2014). In the present

study, each pier of the Kadamtali flyover bridge is

modelled using SeismoStruct 2016 software,

assuming all the loads from superstructures above

pier as a lumped mass over the pier top. This

simplification holds true only when the bridge

superstructure is assumed to be rigid in its own plane

which shows no significant structural effects on the

seismic performance of the bridge system when

subjected to earthquake ground acceleration in

longitudinal direction (Ghobarah et at., 1988). Figure

5 shows the 2-D finite element model with single

degree of freedom system of a pier of Kadamtali

Flyover. In this study for material modeling, bilinear

steel model (stl_bl) has been used for reinforcement




modeling and Mander et al. nonlinear concrete model

(con_ma) has been used for concrete modeling of

superstructure. The sections of piers have been

modelled as original geometric dimension as force

based inelastic frame element (infrmFB) where, 198

section fibres with 5 integration sections have been

used for discretization. The loads from deck,

prestressed concrete girders, box girders and pier

caps are calculated and modelled as lumped mass

element (lmass) on the pier top. The base of the piers

is assumed to be fixed neglecting the foundation

movement effect in the analysis. The nonlinear force-

displacement behaviour of the bridge pier should be

considered in seismic analysis of a bridge system,

especially in a seismically active zone. In such a

region, the bridge piers are expected to incur large

displacements during earthquakes, which lead to the

fact that the linear force-displacement behaviour of a

bridge pier will result in a very uneconomic design

(Khan et. al., 2014).

Fig. 5: Perspective view of Finite element Pier

model of Kadamtali Flyover (SeismoStruct 2016)

Lateral Strength and Ductility Evaluation of

Bridge Piers:

The failure mode, lateral strength and ductility of

bridge piers are computed using the method of

nonlinear static pushover analysis and the analytical

method suggested by Japan Road Association (JRA,

2002). The sectional analysis has been conducted by

professional software Response 2000 to obtain the

moment-curvature relationship of pier cross sections.

In addition, non-linear finite element software

SeismoStruct 2016 is used to conduct the pushover

analysis in order to derive the force-displacement

relationships of piers. Sectional analysis and

nonlinear pushover analysis has been carried out to

obtain the lateral strength and ductility capacity of

the piers.

Moment-curvature Relationship of Pier Cross

Sections

Numerical evaluations of moment curvature of piers

are done by sectional analysis using Response 2000

software. Concrete and rebar stress-strain models are

directly shown in the software after providing the

strength of the materials. The concrete and rebar

stress-strain model used in this study are shown in

Fig. 6. The moment curvature (M-) relationships

for the two available cross-sections of piers are

shown in Fig. 7. The larger cross section of piers can

sustain larger moments than smaller cross section of

piers for the same curvature.

Development of Force-Displacement Relationship for

Piers

Force displacement relationships of piers are

obtained from moment curvature relationship found

from sectional analysis in the previous section on the

basis of guideline provided by JRA 2002. Fig.8

shows numerical evaluation of force displacement

relationship from moment curvature of pier cross-

section.

Fig. 6: Material modeling in Response

2000 software

Fig. 7: The moment curvature (M-) relationships for the

two available cross-sections of piers

0

5000

10000

15000

20000

25000

30000

35000

0 5 10 15 20 25

Mo

me

nt,

M (

kN

-m)

Curvature, (rad/km)

M-ϕ Relationship

section 1200x2500 section 1500x3000




Fig. 8: Numerical evaluation of force displacement relationship from moment curvature (M-) of pier cross-

section (JRA, 2002)

According to JRA 2002, steps for obtaining the

force-displacement relationships at the top of the pier

are as follows:

The pier is divided into N slices along its

height.

The moment-curvature diagrams for each

cross-section are obtained through sectional

analysis.

The horizontal force P is applied at the top

of the pier.

The bending moment diagrams of the pier

for the applied force P are drawn.

The curvature from bending moment and

moment-curvature diagram is obtained.

The displacement, δ at the top of the pier is

estimated using the following Eqn. (1).

(1)

Where, i is the curvature of the pier

section i, dy is the width of the pier cross

section i and di is the distance from the top

of the pier to centre of gravity of section i.

In a similar way, several forces P are

applied and the corresponding

displacements are obtained.

Following the above guidelines force displacement

relationship of piers are formed. Among the piers,

force displacement relationship of pier 10 has been

shown in Fig. 9, where the ultimate displacement ( u)

is found to be 226 mm. The force displacement

relationships of piers can also be obtained from

pushover analysis of piers, which has been done by

SeismoStruct 2016 in this study. Each single pier is

modelled as single degree of freedom system with a

lumped mass on the pier top carrying all the seismic

dead load coming from deck, girder and pier cap.

Figure 10 shows the Pushover model of pier 10

(SeismoStruct 2016) and Fig. 11 shows the force

displacement relationship of pier 10 obtained from

pushover analysis, where the ultimate displacement

( u) is found to be 211 mm. The bilinear idealization

of force displacement relationships can be easily

found in the analysis result in SeismoStruct 2016,

from which yield displacement ( y), ultimate

displacement ( u) and ultimate strength (Pu) are

obtained as shown in Fig. 12.

Fig. 9: Force-Displacement relationship of

Pier 10 (Following JRA, 2002)

Fig.10: Pushover model of Pier 10

(SeismoStruct 2016)

0

1000

2000

3000

0 100 200 300

Fo

rce

(k

N)

Displacement (mm)

Force-Displacement relationship of

Pier 10




Fig.11: Force-Displacement relationship of

Pier 10 (Obtained from pushover analysis)

Fig.12: Bilinear idealization of Force-

Displacement relationship

Similarly, force displacement relationships have been

obtained from pushover analysis of all the piers, from

which yield displacement ( y), ultimate displacement

( u) and ultimate strength (Pu) have been tabulated in

following Table 3 after bilinear idealization.

Table 3: Yield displacement ( y), Ultimate displacement ( u) and Ultimate strength (Pu) of Piers of Kadamtali

Flyover

Pier

No.

Yield

displacement,

y (m)

Ultimate

displacement,

u (m)

Ultimate

Strength,

Pu (kN)

Pier

No.

Yield

displacement,

y (m)

Ultimate

displacement,

u (m)

Ultimate

Strength,

Pu (kN)

1 0.019 0.106 3667

12 0.034 0.197 2658

2 0.020 0.129 3414 13 0.022 0.159 3082

3 0.022 0.157 3092 14 0.020 0.129 3432

4 0.023 0.155 2910 15 0.020 0.122 3446

5 0.035 0.204 2553 16 0.014 0.127 3255

6 0.035 0.199 2573 17 0.020 0.115 3498

7 0.037 0.175 2454 18 0.020 0.119 3321

8 0.024 0.182 3582 19 0.017 0.091 3814

9 0.024 0.181 3589 20 0.018 0.099 3762

10 0.037 0.211 2425 21 0.011 0.063 4577

11 0.037 0.211 2425

Evaluation of Failure Mode, Lateral Strength and

Ductility Capacity of Bridge Piers

The capacity of bridge piers are expressed in terms of

lateral strength and ductility. Failure mode of piers

are analyzed according to the procedure suggested by

Japan Road Association (JRA, 2002), depending on

the flexural strength (Pu), shear strength (Ps) and

shear strength under static loading (Ps0). Failure

mode of a pier is decided to be one of the flexural

failure, shear failure after flexural damage and shear

failure. Lateral strength (Pa) and ductility capacity

(μa) of the piers were also analyzed according the

procedure described by (JRA 2002), depending on

the mode of failure of piers.

Failure

Mode =

Flexural

failure………………………………

…. Pu Ps

Shear Failure after Flexural

Damage ………….. Ps Pu Ps0

(

2)

Shear

Failure………………………………

……. Ps0 Pu

0

500

1000

1500

2000

2500

3000

0 100 200 300

Fo

rce

(k

N)

Displacement (mm)

Force-displacement relationship of Pier 10




Lateral

Strengt

h, Pa =

Pu ………………Flexural failure

Pu ………………Shear Failure after

Flexural Damage

(

3)

Ps0 ……………..Shear Failure

Ductilit

y

Capacit

y, a =

……………..Flexural

failure

1.0…………………………Shear Failure

after Flexural Damage

(

4)

1.0 …………………….…..Shear Failure

Where, α = safety factor depending on importance of

bridges and the type of ground motion (α = 3.0 and

2.4 for important and ordinary bridges, respectively,

under the near field ground motions, and α = 1.5 and

1.2 for important and ordinary bridges, respectively,

under the far field ground motions).

Shear strength of concrete can be calculated by

following equation (JRA, 2002),

(5)

(6)

(7)

Where,

Ps = Shear Strength (N)

Sc = Shear Strength resisted by concrete (N)

Ss = Shear Strength borne by hoop tie (N)

b = Width of pier section (mm)

d = Effective depth of pier section (mm)

Aw = Sectional area of hoop ties arranged with an

interval of and an angle of θ (mm)

= Spacing of the stirrup (mm)

= Yield point of hoop ties (N/mm2)

cc = Modification factor on the effects of alternating

cyclic loading and taken as 0.6 for Type I, 0.8 for

Type II earthquake and 1.0 for calculating Ps0

The values of , ce and cpt are given in Table 4, Table

5 and Table 6

Table 4: Average Shear Stress of Concrete, (N/mm2)

Design Compressive Strength of Concrete, (N/mm2) 21 24 27 30 40

Average Shear Stress of Concrete (N/mm2) 0.33 0.35 0.36 0.37 0.41

Table 5: Modification Factor ce in Relation to Effective Height, d of a Pier Section

Effective Height, d (mm) Below 1000 3000 5000 Above 10000

ce 1.0 0.7 0.6 0.5

Table 6: Modification Factor cpt in Relation to Axial Tensile Reinforcement Ratio, pt

Tensile Reinforcement Ratio (%) 0.2 0.3 0.5 Above 1.0

cpt 0.9 1.0 1.2 1.5

In this study, α is taken as 3.0 assuming important

bridge in near field region and cc as 0.6 assuming

probability of Type I earthquake. All other values

have been calculated as mentioned above. Following

the above guidelines shear strength (Ps) and shear

strength under static loading (Ps0) have been

calculated and failure modes have been determined

using Eqn. (2) as tabulated in Table 7.




Table 7: Pier Failure Mode

Pier No.

Ultimate

Strength,

Pu (kN)

Shear

Strength,

Ps (kN)

Shear

Strength,

[for cc=1]

Ps0 (kN)

Failure

Criteria Failure Mode

1 3667 3002 3509 Ps0 < Pu Shear Failure

2 3414 3002 3509 Ps < Pu s0 Shear Failure after Flexural yielding


4 2910 3002 3509 Pu s Flexural Failure











15 3446 3002 3509 Ps < P s0 Shear Failure after Flexural yielding







On the basis of pier failure mode, pier lateral strength

(Pa) has been evaluated using Eqn. (3) and pier

ductility capacity has been determined using Eqn. (4)

as tabulated in Table 8.




Table 8: Pier Lateral Strength and Ductility Capacity

Pier No. Pier Lateral Strength Pier Ductility Capacity

Pa Pa (kN) μa

1 Pa = Ps0 3509 1.00

2 Pa = Pu 3414 1.00

3 Pa = Pu 3092 1.00

4 Pa = Pu 2910 2.90

5 Pa = Pu 2553 2.60

6 Pa = Pu 2573 2.55

7 Pa = Pu 2454 2.26

8 Pa = Pu 3578 3.19

9 Pa = Pu 3589 3.19

10 Pa = Pu 2425 2.59

11 Pa = Pu 2425 2.59

12 Pa = Pu 2658 2.62

13 Pa = Pu 3082 1.00

14 Pa = Pu 3432 1.00

15 Pa = Pu 3446 1.00

16 Pa = Pu 3255 1.00

17 Pa = Pu 3498 1.00

18 Pa = Pu 3321 1.00

19 Pa = Ps0 3509 1.00

20 Pa = Ps0 3509 1.00

21 Pa = Ps0 3509 1.00

Seismic Safety Evaluation of Bridge Piers

Evaluation of the safety of existing bridge piers to

withstand imposed seismic loads requires assessment

and comparison of anticipated demand and available

capacities. Three spectral accelerations

corresponding to three peak ground accelerations

(PGA) of 0.15g, 0.28g and 0.36g as obtained from

the design response spectra [BNBC 2006 and BNBC

2012(Draft)] are used in safety evaluation. The safety

of the bridge piers are evaluated according to the

guidelines of JRA, 2002. Lateral force demand for a

particular spectral acceleration is determined using

the following Eqn. 8

(8)

Where, Sa is the spectral acceleration, W is the

seismic dead load, g is the acceleration due to gravity

and R is the response modification factor. The

response modification factor, R can be found from

following Eqn. 9.

(9)

The safety of bridge piers against spectral

acceleration corresponding to a PGA of 0.15g are

tabulated in Table 9. It is seen from the results that all

the piers are in "Safe' stage. The results of safety

analysis against spectral accelerations corresponding

to a PGA of 0.28g and 0.36g are shown in Tables 10

and Tables 11 respectively.




Table 9: Safety Evaluation of Piers for a PGA of 0.15g

Pier

No.

Response

Modification

Factor, R

Seismic

Weight,

W (kN)

Spectral

Acceleration,

Sa (m/s2)

Lateral Force

Demand,

Pdemend (kN)

Pier Lateral

Strength,

Pa (kN)

Safety Status

1 1.00 4756.50 3.68 1784 3509 Safe

2 1.00 5998.87 3.68 2250 3414 Safe

3 1.00 6199.98 3.68 2326 3092 Safe

4 2.19 5014.49 3.68 858 2910 Safe

5 2.05 4757.62 3.68 871 2553 Safe

6 2.02 4320.99 3.68 801 2573 Safe

7 1.88 3987.90 3.68 797 2454 Safe

8 2.32 6042.28 3.68 976 3578 Safe

9 2.32 6159.55 3.68 996 3589 Safe

10 2.04 4546.84 3.68 835 2425 Safe

11 2.04 4546.84 3.68 835 2425 Safe

12 2.06 5162.74 3.68 942 2658 Safe

13 1.00 6242.46 3.68 2342 3082 Safe

14 1.00 6414.52 3.68 2406 3432 Safe

15 1.00 5497.35 3.68 2062 3446 Safe

16 1.00 4636.66 3.68 1739 3255 Safe

17 1.00 4606.42 3.68 1728 3498 Safe

18 1.00 4627.30 3.68 1736 3321 Safe

19 1.00 4569.70 3.68 1714 3509 Safe

20 1.00 4576.18 3.68 1717 3509 Safe

21 1.00 4504.90 3.68 1690 3509 Safe


Pier

No.

Response

Modification

Factor, R

Seismic

Weight,

W (kN)

Spectral

Acceleration,

Sa (m/s2)

Lateral Force

Demand,

Pdemend (kN)

Pier Lateral

Strength,

Pa (kN)

Safety Status

1 1.00 4756.50 6.87 3331 3509 Safe

2 1.00 5998.87 6.87 4201 3414 Unsafe

3 1.00 6199.98 6.87 4342 3092 Unsafe

4 2.19 5014.49 6.87 1602 2910 Safe

5 2.05 4757.62 6.87 1626 2553 Safe

6 2.02 4320.99 6.87 1496 2573 Safe

7 1.88 3987.90 6.87 1488 2454 Safe

8 2.32 6042.28 6.87 1823 3578 Safe

9 2.32 6159.55 6.87 1859 3589 Safe

10 2.04 4546.84 6.87 1558 2425 Safe

11 2.04 4546.84 6.87 1558 2425 Safe

12 2.06 5162.74 6.87 1758 2658 Safe

13 1.00 6242.46 6.87 4372 3082 Unsafe

14 1.00 6414.52 6.87 4492 3432 Unsafe

15 1.00 5497.35 6.87 3850 3446 Unsafe

16 1.00 4636.66 6.87 3247 3255 Safe




17 1.00 4606.42 6.87 3226 3498 Safe

18 1.00 4627.30 6.87 3241 3321 Safe

19 1.00 4569.70 6.87 3200 3509 Safe

20 1.00 4576.18 6.87 3205 3509 Safe

21 1.00 4504.90 6.87 3155 3509 Safe


Pier

No.

Response

Modification

Factor, R

Seismic

Weight,

W (kN)

Spectral

Acceleration,

Sa (m/s2)

Lateral Force

Demand,

Pdemend (kN)

Pier Lateral

Strength,

Pa (kN)

Safety Status

1 1.00 4756.50 8.83 4281 3509 Unsafe

2 1.00 5998.87 8.83 5400 3414 Unsafe

3 1.00 6199.98 8.83 5581 3092 Unsafe

4 2.19 5014.49 8.83 2059 2910 Safe

5 2.05 4757.62 8.83 2090 2553 Safe

6 2.02 4320.99 8.83 1923 2573 Safe

7 1.88 3987.90 8.83 1913 2454 Safe

8 2.32 6042.28 8.83 2343 3578 Safe

9 2.32 6159.55 8.83 2390 3589 Safe

10 2.04 4546.84 8.83 2003 2425 Safe

11 2.04 4546.84 8.83 2003 2425 Safe

12 2.06 5162.74 8.83 2259 2658 Safe

13 1.00 6242.46 8.83 5619 3082 Unsafe

14 1.00 6414.52 8.83 5774 3432 Unsafe

15 1.00 5497.35 8.83 4948 3446 Unsafe

16 1.00 4636.66 8.83 4173 3255 Unsafe

17 1.00 4606.42 8.83 4146 3498 Unsafe

18 1.00 4627.30 8.83 4165 3321 Unsafe

19 1.00 4569.70 8.83 4113 3509 Unsafe

20 1.00 4576.18 8.83 4119 3509 Unsafe

21 1.00 4504.90 8.83 4055 3509 Unsafe

All the piers of Kadamtali flyover are found safe

when subjected to earthquake with PGA of 0.15g but

some piers with failure mode of “shear failure after

flexural yielding” are not safe when subjected to

earthquake with PGA of 0.28g and all the piers with

failure mode of “shear failure after flexural yielding”

and “shear failure” are not safe when subjected to

earthquake with PGA of 0.36g. All the piers with

failure mode of “flexural failure” are safe in

earthquakes having all three types of PGA considered

in the study.

Conclusion:

Lateral strength and safety of the piers under

different spectral acceleration of Kadamtali Flyover

have been analytically evaluated using the methods

as suggested by Japan Road Association (JRA, 2002)

considering the different modes of failure. Analytical

model of bridge piers has been governed using

specified software for seismic analysis, SeismoStruct

2016, considering material and geometrical

nonlinearities. Moment curvature relationships of

pier sections along with force displacement

relationships of piers are used to identify yield

displacement, ultimate displacement, ultimate

flexural capacity and JRA 2002 guidelines are used

to determine shear capacity of piers eventually,

leading to the determination of failure mode, lateral

strength capacity and ductility capacity of piers. Tall

piers are found to be vulnerable to flexural failure

whereas the relatively short piers are susceptible to

shear failure rather than flexural failure. Pier 9 has

been found with largest lateral strength whereas pier

10 and pier 11 can sustain smaller lateral force

compared to the other piers. In terms of ductility

capacity, pier 8 and pier 9 have the largest ductility

capacity of 3.19. Finally, the seismic safety of piers

of the flyover has been evaluated using the ductility

method for three different earthquake ground motion

intensity having PGA of 0.15g, 0.28g and 0.35g.

Comparing the seismic demand corresponding to




different PGA with the seismic capacity, safety status

of piers has been obtained. All the piers with failure

mode of “flexural failure” are safe in earthquakes

having all three types of PGA considered in the

study. But pier 2, 3, 13, 14 and 15 are found to be

unsafe during the earthquakes with both PGA of

0.28g and 0.36g. However, pier 1, 16, 17, 18, 19, 20

and 21 are found to be unsafe only during the

earthquakes with PGA of 0.36g.

References:

[1] Alam, M.J., (2011), Earthquake Risk in

Bangladesh, University of Kassel, [online],

Available at:

http://www.unikassel.de/fb14/stahlbau/earth

eng/downloads/Earthquake%20risk%20in%

20Bangladesh%20Prof.%20Jahangir%20Al

am.pdf [Accessed 20July, 2016].

[2] Al-Hussaini, T.M., Hossain, T.R. and Al-

Noman, M.N., (2012), “Proposed Changes

to the Geotechnical Earthquake Engineering

Provisions of the Bangladesh National

Building Code”, Geotechnical Engineering

Journal of the SEAGS & AGSSEA, Vol.

43(2): 1-7.

[3] Alim, H., Khan, A.K.M. T. A. and Bhuiyan,

M. A. R., (2014), “Seismic Safety

Evaluation of Bahaddarhat Highway

Bridge”, 2nd International Conference on

Advances in Civil Engineering, pp. 426-437.

[4] Bilham, R., (2004), “Earthquakes in India

and the Himalaya: tectonics, geodesy and

history”, Annals of Geophysics, Vol. 47

(2/3): 839-858.

[5] Ghobarah, A. and Ali, H. M., (1988),

“Seismic Performance of Highway

Bridges”, Engineering Structures, Vol.

10(3), pp. 157–166.

[6] Hwang, H., Liu, J. B. and Chiu, Y., (2001),

“Seismic Fragility Analysis of Highway

Bridges” Technical Report of MAEC RR-4

project, Mid-America Earthquake Center.

[7] Japan Road Association (JRA) (2002),

“Specifications for Highway Bridges - Part

V: Seismic design”, Tokyo, Japan.

[8] Khan, A.K.M. T. A., Alim, H. and Bhuiyan,

M. A. R., (2014), “Lateral strength and

ductility of piers of Bahaddarhat overpass in

Chittagong, Bangladesh”, Journal of Civil

Engineering (IEB), Vol. 43 (1) (2015): 93-

104.

[9] Morino, M., Kamal, A.S.M.M., (2003),

“Report of active fault mapping in

Bangladesh: Paleo-seismological study of

the Dauki fault and the Indian-Burman plate

boundary fault, Comprehensive Disaster

Management Programme (CDMP II)”,

Ministry of Disaster Management and

Relief, Govt. of Bangladesh, pp. 3-9.

[10] Mukhlis, M. R., Tangina, S. A., Mostazid

M. I. and Hoque, M. R., (2016), “Seismic

Vulnerability Assessment of Existing

Buildings in Chittagong City: A Case Study

on Rampur Ward”, 3rd International

Conference on Advances in Civil

Engineering, pp. 331-336.

[11] UPSeis, 2016, Where Do Earthquakes

Happen, Michigan Technological

University, [online], Available at:

http://www.geo.mtu.edu/UPSeis/where.html

[Accessed 21July, 2016].

http://www.unikassel.de/fb14/stahlbau/eartheng/downloads/Earthquake%20risk%20in%20Bangladesh%20Prof.%20Jahangir%20Alam.pdf







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