eurasian journal of science & engineering issn 2414-5629

Eurasian Journal of Science & Engineering

ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE

Volume 2, Issue 1; December, 2016

EDITOR-IN-CHIEF

Dr. Duran Kala, Ishik University, Iraq

EDITORIAL ASSISTANT

Çağrı Tuğrul Mart, Ishik University, Iraq

MEDIA REVIEW EDITOR

Mustafa Albay, Ishik University, Iraq

ASSOCIATE EDITORS

Prof. Dr. Ahmet Öztaş, Ishik University, Iraq

Prof. Dr. Zafer Ayvaz, Ege University, Turkey

Prof.Dr. Ozgur Kisi, International Black Sea University, Georgia

Prof. Dr. Bayan Salim, Ishik University, Iraq

Prof. Dr. Yassin Al-Hiti, Ishik University, Iraq

Prof. Dr. Nabil A. Fakhre, Salahaddin University, Iraq

EDITORIAL BOARD MEMBERS

Assoc. Prof. Dr. Amir Nurullayevich, Russian State Geological Prospecting University, Russia

Assoc. Prof. Dr. Thamir M. Ahmad, Ishik University, Iraq

Assoc. Prof. Dr. Cihan Mert, International Black Sea University, Georgia

Assoc. Prof. Dr. Hassan Hassoon Aldelfi, Ishik University, Iraq

Assoc. Prof. Dr. Suat Karadeniz, Ishik University, Iraq

Asst. Prof. Dr. Cevat Onal, Nigerian Turkish Nile University, Nigeria

Asst. Prof. Dr. Omer Eskidere, Nigerian Turkish Nile University, Nigeria

Asst. Prof. Dr. Serkan Dogan, International Burch University, Bosnia and Herzegovina

Asst. Prof. Dr. Jasmin Kevric, International Burch University, Bosnia and Herzegovina

Asst. Prof. Dr. Nejdet Dogru, International Burch University, Bosnia and Herzegovina

Dr. Mehmet Özdemir, Ishik University, Iraq

Dr. Mutlay Dogan, Ishik University, Iraq

Dr. Doğan Özdemir, Ishik University, Iraq

Dr. Halit Vural, Ishik University, Iraq

Dr. Cumhur Aksu, Ishik University, Iraq

Dr. Gunter Senyurt, Ishik University, Iraq

Dr. Selcuk Cankurt, Ishik University, Iraq

Dr. Zakariya Adel Hussein, Koya University, Iraq

Editorial Office:


Ishik University, Erbil, Iraq

www.eajse.org

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Eurasian Journal of Science & Engineering gratefully acknowledges the support of Ishik University.

Eurasian Journal of Science & Engineering is particularly indebted to Ishik University Research Center.

Copyright © 2016

All Rights Reserved

Composed by Irfan Publishing, Erbil, Iraq

Printed by Anıl Press, Gaziantep, Turkey

No responsibility for the views expressed by the authors in this journal is assumed by the editors or by

Eurasian Journal of Science & Engineering.

EAJSE (Eurasian Journal of Science & Engineering) is published biannually (December, June) in both print

and online versions by Ishik University.




Table of Contents

1. Pressure Coefficients of Curved Lip of Vertical Lift Gate in

Dam Tunnels………………………………………………………………………….……1

Author: Thamir Mohammed Ahmed

2. Effects of Increasing the Base on Concrete Dam Stability……………………...……..10

Author: Thamir Mohammed Ahmed

3. The Residual Strength for Different Shaped High Strength Concrete Specimens

at High Temperature……………………………………………………………………..21

Authors: Rahel Khalid Ibrahim & Hiba Muhammed Muhammedemin

4. Assessment of Strengthening Scheme of Existing Buildings Extended by Adding

Additional Floors……………………………………………………………………...….28

Author: Bayan S. Al-Nu’man

5. The Critical Links between Socio-Demographic Dynamics of Sundarbans Impact

Zone and Forest Resource Depletion, Bangladesh: A Review…………………………41

Author: Sanaul Haque Mondal




1

Pressure Coefficients of Curved Lip of Vertical Lift Gate in Dam Tunnels

Thamir Mohammed Ahmed

1

1Civil Engineering Department, Ishik University, Erbil, Iraq

Correspondence: Thamir Mohammed Ahmed, Ishik University, Erbil, Iraq.

Email: [email protected]

Received: September 12, 2016 Accepted: November 23, 2016 Online Published: December 1, 2016

doi: 10.23918/eajse.2414211

Abstract: The vertical lift gate shaft is installed across the dam tunnel to regulate the flow rate passing

toward the downstream side to satisfy the water demand in addition to the power generation

requirements. The flow through the shaft is mostly divided into two parts, over and below the gate,

and as a result, two forces will be created, vertically ,downward and upward on both top and bottom

gate surfaces. The difference between these forces produces so-called hydrodynamic force or hydraulic

downpull force which has a vital effect on gate operation, so that in the case of negative values, this

force will prevent the closure of the gate. The downpull force influences by many parameters, however,

the geometry of gate is considered as one of the most common effective factor that influence the values

and behavior of downpull force. In present study, physical hydraulic model is used to assess the effects

of different rounded gate lip shapes on downpull force with respect to different gate opening ratios.

The variation of bottom pressure coefficient along the gate surface has also been studied and the

results are discussed.

Keywords: Downpull, Pressure Coefficient, Rounded Gate Lip

1. Introduction

The vertical lift gates subjected to many hydrodynamics forces due to the potential of pressurized

water flow passing through the dam tunnel. The water flow just before the gate shaft takes two

directions above and beneath the gate and in accordance with that, two vertical forces with opposite

directions will created. The net force that has been obtained from the difference of these two forces,

and called as downpull force, is considered an important reference for safe and economic design of

the gates.

Many hydraulic and geometrical parameters affect the downpull force and have been studied by

many researchers which their researches based upon one or both of experimental and mathematical

approaches. The flow conditions, gate lip geometrics have been examined and a lot of results were

analysed and suggestions being recommended. The effects of aeration, gate lip shape and the

clearances sizes on forces issued by pressurized flow and hence on the gate stability was studied by

Cox et al (1960).The study was used as guidance for next researches. The force exerted by air

tunnel flow on vertical lift gate has received a great attention by Naudascher et al (1964).The

effects of different flow conditions and gate lip shapes were considered and the main results were

formulated by the following expressions:




2

( ) (1)

Where:

= downpull force, N,

( ) ,

( )

= gate width, m,

= gate thickness, m

= water mass density, N/m3, and

= velocity of the contracted jet issuing from underneath the gate, m/sec.

= Piezometric head on gate top surface,

=Piezometric head just downstream the gate shaft m, and

=Piezometric head at a point on the gate bottom, m.

Two empirical methods were suggested by Sagar (1977) to evaluate the downpull forces, first one

named as downpull coefficient which is based on Fort Randall Dam data, and the second is termed

as pressure distribution method which is most common and based on estimating the forces acting

on the top and bottom surfaces of the gate. These two methods are applicable for similar gate

shapes.

The intensity of pressure and its distribution pattern were studied by Bhargava and Narasimhan

(1989) for the gate under the specific frequencies and amplitude of vertical vibration was obtained

by the integrating of the pressure fluctuations profiles over the gate thickness was used to obtain

the total intensity of pressures on vibrating gates. The study specifies a pressure of common

frequency which is considered as critical condition for gate design.

The effects of vibration created by the separation and reattachment of flow along the vertical lift

gate bottom surface were examined by Thang (1990). The different lip geometries and flow

conditions were considered and the study revealed that the fluctuation was caused by combined

action of the vortices established just upstream the gate and unbalanced shear layer below the gate.

The analysis leads to indicate the critical range of gate opening corresponding to potential gate

vibrations.

The one dimensional finite element model based upon the velocity and mean pressure distribution

along the bottom gate surface conducted by Al-Kadi (1997). The model was verified with the

results of analytical prediction and gave a good agreement. The experimental work was conducted

by Ahmed (1999) to study the effect of many gate geometries on downpull force. The study

concludes that the downpull coefficient is influenced significantly by gate geometry and gate




3

opening.

The experimental pressure distribution measurements along the bottom surface of different gate

geometries were carried out by Aydin et al (2006). The results of measurements were used to

evaluate the downpull forces for both cases of stationary and closing modes. The results of

measurements were verified with the Predicted mathematical model order to confirm its validity.

The high head smooth upstream gate face of was exhibited by Markovic et al (2013) to study the

effects vertical opening installed within the gate body on hydrodynamic forces. It is found from

the various attempts of tests on different models that an expansion in vertical openings of the gate

leaf will lead to produce significant reduction on hydrodynamic forces.

The ANSYS FLUENT programming was used by Uysal in 2014 to predict the downpull forces on

intake gate of dam tunnel. The results obtained from the mathematical model were compared with

experimental measurements and a very good agreement was observed.

The random hydraulic model was used by Taher et al (2016) to study the effects of different gate

lips shapes on the values and distribution of downpull force. The study concluded that the gate

openings ratios have inversely effects on values of bottom pressure coefficient (Kb) and hence on

downpull force. In addition, the study indicated that the gate lip geometry influences the behavior

of stream lines due to their attachment and reattachment and accordingly the values of (Kb) are

affected.

In the current study, the pressure fluctuation on two different curved gate lip shapes of vertical lift

gate is examined. The study investigated numerous hydraulic parameters that influence the values

and distributions of pressure heads for various gate openings. The validity of the results is indicated

by the comparison with corresponding cases of previous related works.

2. Experimental Set Up

The measurements were conducted in a rectangular glass recycling flume, 4m long, 0.2 m wide,

and 0.3 m deep with horizontal steel bottom floor. The top of flume was covered by thick plate

representing tunnel. The gate model made by thick plate (0.5 m x0.2 mx0.05 m) and supported by a

steel frame slides in the vertical path of the steel gate shaft (1m x 0.3 m x 0.15 m). The gate can be

adjusted by a screw placed on the top cover of the shaft to control the gate openings. The end of

tunnel model was provided by control gate to satisfy the requirements of pressurized flow. The

schematic layout of the tunnel is shown in Fig.(1-A).




4

Figure 1: Schematic layout of the tunnel

Ten taps with 4 mm diameter for pressure head measurements were drilled on two parallel lines

along the gate bottom surface .The first and second five taps were located at distances of 0.25 B

and 0.5 B respectively from the gate edge. A small length of steel pipe of the same diameter

inserted in each tap and then connected to piezometers board through plastic tubes. Two pito-tubes

were installed upstream and downstream the gate shaft one to measure the mean velocity and the

other for jet velocity just below the the gate. Fig. (1-B) shows the main details of gate model.

3. Results and Discussion

The experiments were conducted by the run of hydraulic model and the required measurements

regarded to evaluating the downpull force were carried out.The top and bottom piezometric heads

are necessary for determination of the top and bottom pressure coefficients (Kt and Kb) and

consequently the downpull force coefficient. In current study, the attempts are made to investigate

the influence of rounded edge of gate lip ( r/d=1 and r/d=1.5) on the pressure coefficients as well as

on the distribution of piezometric heads along the bottom gates surface and the values of all

coefficients (Kt,Kb, and Kd) were obtained by using equation (1).

Figure 2 shows the variation of downpull coefficients with gate opening ratios for rounded gate lip

shape with (r/d=1). It can be seen from the figure that top pressure coefficient (Kt) is uniformly

varied with gate opening ratios and no significant change in values are observed. However, the

intangible variance in values of bottom pressure coefficient (Kb) is appeared, which means that the

downpull coefficient (Kd) is influenced mainly by (Kb) values. The (Kb) profile started from low

values for gate opening ratio (Y/Yo=10%) and increased up to (Y/Yo=30%) beyond which the

(Kb) profile moved with approximately constant values (Kb=0.6) and then increased obviously to

attain the maximum values when (Y/Yo) becomes more than (70%).The sudden increase in (Kb)

values caused the downpull coefficients to be negative for (Y/Yo ≥75%).The main conclusion

states that the large gate openings lead to increase bottom pressure coefficient )(Kb) and reduce the

values of downpull coefficient (Kd) Which indicates the probability of a problem on the prevention

of occurrence of the closure of the gate.




5

Figure 2: The variation of downpull coefficients with gate openings for r/d=1

Figure (3) with (r/d=l) and (Y/Yo =10%, 20%, 30% and 40%) reveal that (Kb) values are dropped

uniformly with from its maximum values (Kb=0.8) at the leading edge up to (Kb=0) at trailing

edge except (Y/Yo=10%) where the minimum (Kb) value ended at (0.4). However, the general

view of (Kb) distribution indicated that the uniform decrease in values of (Kb) kept the flow stream

lines with poor attachment to the bottom gate surface and no separation has been occurred.

Figure 3: The variation of bottom pressure coefficient (Kb) along the bottom gate surface for each

gate openings

Figure(4) shows the distribution of (Kb) values with (X/d) for (Y/Yo=50%, 60%, 70%, 80% and

90%).A general reduction in (Kb) values from leading edge toward trailing edge is observed

especially for gate opening ratios of (Y/Yo=50%,60% and 70%) ,whereas, a relative higher values

with same trend are indicated for (Y/Yo=80% and 90%) .As it can be noticed from the figure, that

the (Kb) values are greater than those of low (Y/Yo) showed in figure (3), thus , a strong

attachment of flow stream lines with the bottom gate surface is established and referred to better

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1

(Kt,

Kb

,Kd

)

(Y/Yo%)

(r/d=1)

Kt

Kb

Kd

0

0.2

0.4

0.6

0.8

1

0 0.5 1

(Kb

)

(X/d)

(r/d=1)

Kb (Y/Yo=10%)

Kb (Y/Yo=20%)

Kb (Y/Yo=30%)

Kb (Y/Yo=40%)




6

level of gate stability due to less probability of vibration occurrence.

Figure 4: The variation of bottom pressure coefficient (Kb) along the bottom

gate surface for each gate openings

The effects of rounded gate lip shape with (r/d=1.5) on downpull coefficients has also been studied

.Figure (5) demonstrates that the (Kb) values profile decreased rapidly from high value at

(Y/Yo=10%) toward low approximately uniform values along the gate opening ratios (Y/Yo= 20%,

30%, 40% and 50%).The increase in (Y/Yo) more than (50%) accompanied with sudden rising in

(Kb) profile so that the maximum (Kb) values are attained and varied slightly for remaining large

(Y/Yo) values. In view of slight change of (Kt) values profile, the downpull coefficient (Kd) values

are influenced effectively by (Kb) values. Consequently, the high values of (Kb) lead to decrease

(Kd) values to the extent that it generated negative values and could pose a challenge and a

problem for the possibility of gate closing as indicated for gate opening ratio (Y/Yo=80%).

Figure 5: The variation of downpull coefficients with gate openings for r/d=1.5

Due to the determinants of rounded gate lip shape with (r/d=1.5) which did not accommodate all

five taps , only the middle three taps were used rather than five to measure the bottom pressure.

Figure (6) shows the variation of (Kb) values along the bottom gate surface for gate opening ratios

(Y/Yo =10%, 20%,30% and 40%) .It is obvious from the figure that for distance between

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1

(Kb

)

(X/d)

(r/d=1)

Kb (Y/Yo=50%)

Kb (Y/Yo=60%)

Kb (Y/Yo=70%)

Kb (Y/Yo=80%)

Kb (Y/Yo=90%)

-0.5

0

0.5

1

1.5

0 0.2 0.4 0.6 0.8 1

(Kt,

Kb

,Kd

)

(Y/Yo%)

(r/d=1.5)

Kt

Kb

Kd




7

(X/d=0.4) and (X/d=0.6), The (Kb) values are changed from high to low values and continue with

invariant values toward the trailing edge. Also the figure indicates that at trailing edge, the (Kb)

value for (Y/Yo=40%) is less than others considered ate opening ratios.



Figure (7) indicates that the (Kb) values are decreases as (X/d) increases toward the trailing edge;

furthermore, the general rate (Kb) values are increased as gate opening ratios increased. Hence a

poor attachment of flow is observed for small gate opening ratios which accordingly may lead to

some extent of gate instability.



3.1. Comparison with Previous Works

Naudascher, et al (1964) [12], were used the analytical method for determining downpull forces

based on the effects of gate geometries and jet velocity through vena-contracta under the gate. The

downpull force was estimated as the difference between the top and bottom pressure coefficients

which applied for various gate lip shapes including the rounded lips with different ratios of (r/d).

Figure (8) shows the comparison between the results of (Kb) obtained from the current study where

0

0.2

0.4

0.6

0.8

0 0.5 1

(Kb

)

(X/d)

(r/d=1.5)

Kb( Y/Yo=10%)

Kb (Y/Yo=20%)

Kb (Y/Yo=30%)

Kb (Y/Yo=40%)

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1

(Kb

)

(X/d

(r/d=1.5)

Kb (Y/Yo=50%)

Kb (Y/Yo=60%)

Kb (Y/Yo=70%)

Kb (Y/Yo=80%)




8

gate lip shapes are with (θ=45o and r/d= 1 and 1.5 ) and those obtained from [12] where (θ=45

o and

r/d=0.4) .It can be seen from the figure that the (Kb) values for gate lip shapes with (θ=45o and r/d=

0.4) are decreases from high values at small gate openings up to (Kb=0.6) which created for

(Y/Yo=30% up to 90). A slight change in (Kb) values along all gate opening ratios is observed for

gate lip shape with (θ=45o and r/d=1) which has a greater values than other considered gate lip

shapes. Accordingly, it is expected that in the case of invariant top pressure values, the downpull

force will be greater with gate lip shape of (θ=45o and r/d=0.4) which may lead to prefer the gate

lip shape with (θ=45o and r/d= 1) to be considered due to the limited impact of downpull force, in

addition to ease of manufacturing this shape specifications when compared with other forms of

gates. The figure also shows a clear non- uniformity of (Kb) values for gate lip shape with (θ=45o

and r/d=1.5), the values of (Kb) are decreased as the gate opening ratios increased up to ((Y/Yo=

40%) and then turn to increase with the increase in gate opening ratios and reached its maximum

values beyond (Y/Yo=60%).



4. Conclusions

Based on the current work, pressures coefficients for new cases of (r/d) of vertical lifts are

presented, and the following conclusions can be drawn:

1-The top pressure coefficient values (Kt) are slightly changed with gate opening ratios and seem

to be independent to gate geometries and hence have no significant effects on distribution of

downpull coefficients.

2- It is found that for gate lip shape with (θ=45o and r/d=1) , the (Kb) values increase as the (Y/Yo)

increases whereas for (θ=45o and r/d=1.5) are dropped rapidly from high value at (Y/Yo=10%)

toward low values along the gate opening ratios (Y/Yo= 20%, 30%, 40% and 50%) and then

suddenly turned up to attain maximum values for remaining (Y/Yo) values.

3- The (Kd) values for (θ=45o and r/d=1) are decreased continuously and reached near negative

values at large gate openings and such case is earlier occurred for (θ=45o and r/d=1.5) where the

gate opening ratio (Y/Yo ≥ 50%).

4-The (Kb) values for (θ=45o, r/d=1and r/d=1.5) and all gate openings ratios are generally

decreased along the bottom gate surface and hence a poor attachment has been indicated especially

near the trailing edge of gate.

0

0.5

1

1.5

0 0.2 0.4 0.6 0.8 1

(Kb

)

(Y/Yo%)

r/d=1(θ=45°) r/d=1.5 (θ=45°) r/d=0.4 (θ=45°)(ref.12)




9

5-The large gate openings leads to increase (Kb) values.

6- The values of (Kb) for (θ=45o and r/d=1) are higher than those obtained for (θ=45

o and r/d=0.4)

[12], and accordingly, it can be stated based on this work that in the case of invariant top pressure

values ,the downpull force will be greater with gate lip shape of (θ=45o and r/d=0.4). In general, the

magnitudes of downpull force obtained from the use of lip shape with (r/d = l) are less than those of

( r/d=0.4 and r/d=l .5).

7-The (Kb) values of the (θ=45o and r/d=1.5) are approximately close to those for (θ=45

o and

r/d=1) just for (Y/Yo≥60%).

References

Ahmed, T. M. (1999). Effect of Gate Lip Shapes on the Downpull Force in Tunnel Gates

Experimental Study of Pressure Coefficient along Inclined Bottom Surface of Dam Tunnel

Gate”, Ph.D Thesis submitted to the College of Engineering, University of Baghdad.

AL-Kadi, B. T. (1997). Numerical Evaluation of Downpull Force in Tunnel Gates, Ph.D Thesis

submitted to the College of Engineering, University of Baghdad.

Aydin, I., Ilker T. T., & Onur D. (2006). Prediction of downpull on closing high head gates.

Journal of Hydraulic Research, 44(6), 822-831.

Bhargava, Ved P., & Narasimhan, S. (1989). Pressure fluctuations on gates. Journal of Hydraulic

Research, 27(2), 215-231.

Cox Robert G., Ellis B. P., & Simmons, W.P. (1960). Hydraulic Downpull on High head Gates,

ASCE Discussion Hy.

Markovic–Brankovic, J., & Helmut D. (2013). New High Head Leaf Gate Form with Smooth

Upstream Face. Tem Journal, 3.

Naudaschers E., Helmut E. K., & Ragam R. (1964). Hydrodynamic Analysis for High head Leaf

Gates, ASCE, 90(3).

Sagar, B.T.A. (1977). Downpull in High-head Gate Installations, Parts 1, 2, 3. Water Power Dam

Construct. (3), 38–39; (4), 52–55; (5), 29–35.

Taher, T. M., & Awat O. A. (2016). Effects of Gate Lip Orientation on Bottom Pressure

Coefficient of Dam Tunnel Gate. Arabian Journal for Science and Engineering, 1-10. DOI

10.1007/s13369-016-2202-7, (2016)

Thang, N. D. (1990). Gate vibrations due to unstable flow separation. Journal of Hydraulic

Engineering, 116(3), 342-361.

Uysal, M. A. (2014). Prediction of downpull on high head gates using computational fluid

dynamics. Diss. Middle East Technical University.




10

Effects of Increasing the Base on Concrete Dam Stability

Thamir Mohammed Ahmed1

1Civil Engineering Department, Ishik University, Erbil, Iraq

Correspondence: Thamir Mohammed Ahmed, Ishik University, Erbil, Iraq.


Received: October 12, 2016 Accepted: November 17, 2016 Online Published: December 1, 2016

doi: 10.23918/eajse.2414212

Abstract: The concrete dam is one of the most important hydraulic infrastructures which play a vital

role in providing a wide range of water services and helps prevent many potential disasters such as

floods. The concrete dam subjected to many kinds of static and hydrodynamic forces which almost

needs taking into account of design under different circumstances to satisfy the safety requirements.

The shape of dam is pertinent to the stability of dam regarding the major forces and stresses. One of

the most common ways which is necessary to solve the problems in design due to the cases of unsafely

for any mode of failures is to add mass to the dam upstream face. In this work, a parametric study is

made to investigate the effects of the increase in the base of dam on the principal and shear stresses

developed in the dam. In all cases, all the relevant factors of safety are satisfied. The stability analysis

for all possible modes of failures is carried out to check the performance of the initial section of dam

due several loading conditions. Parameters of importance are studied, discussed and conclusions are

drawn.

Keywords: Concrete Dams, Dams Stability

1. Introduction

Concrete dam is considered as one of giant and strategic hydraulic structures that support a wide

range of high water heads in its reservoir and perform important functions relating to the water

resources management and power generation. The dam is exposed to many types of static and

dynamic loads and hence the stresses arising throughout the body of dam. All these forces may

threat the stability of dam, thus, measures to ensure dam safety should intervene in the designer

accounts. The material density and the geometry of such structures will bear the bulk of the

resistance forces and stresses resulting therefrom. For the sake of the dam safety assurance, all

modes of the expected failure should be subject to scientific examination and analysis starting with

the primary section of design. Types of expected failures are linked to the types of forces and

stresses in the required design and associated with the conditions and restrictions of the

construction site as well as the nature of the functions achieved by dam establishment.

2. Previous Works

Many researches have been paid much more attention for stability analysis of concrete dam due its

importance to satisfy the safety requirements for all considered modes of failures. M. Leclerc, et al

(2003) used the CADAM software to evaluate the stability analysis for concrete dams regarding to




11

many cases such as, compute crack lengths, and safety factors in addition to, (a) crack initiation

and propagation, (b) effects of drainage and cracking under static, seismic, and post-seismic uplift

pressure conditions, and (c) safety evaluation formats (deterministic allowable stresses and limit

states, probabilistic analyses using Monte Carlo simulations).

The U.S.B.R. recommendations in seismic zone II of Bangladesh were used by Hazrat Ali, et al

(2011) to design high concrete gravity dams. The different intensities of earthquakes horizontal

component values which ranged from 0.10 g - 0.30 g with 0.05 g increment were used in carrying

out the analysis. The analysis based upon the techniques of 2D gravity method, finite element

method and ANSYS 5.4. The loads are considered to be constant whereas only the earthquake

forces have been examined for various values. The study concluded that the righting moment is

decreased with the increment of horizontal earthquake intensity and the construction of dam would

not be possible in the case of horizontal component of earth quake intensity with more than 0.3 g.

The impact of earthquakes on Rupsiabagar Khasiyabara dam situated in Pithoragarh district of

Uttarakhand in India is studied by Aryak et al (2012).The CADAM software is used to check

whether the modify of structure by the seismic retrofitting is needed to improve the resistance of

dam to earthquake. The peak value of ground acceleration is considered to ensure the safety of dam

under the effects of different loading conditions which found as safe.

A two-stage procedure was proposed by Arnkjell (2013) for the elastic analysis phase of seismic

design and safety evaluation of concrete gravity dams. The study is based upon the implantation of

response spectrum analysis (RSA) and response history analysis (RHA) results to check the

response of concrete dam to the effects of earthquake forces. Some modifications has been made to

increase the performance of these soft wares and to cover a wide ranges of stability analysis cases.

In addition, a comprehensive evaluation of the accuracy of the RSA procedure has been conducted,

demonstrating that it estimates stresses close enough to the "exact" results (determined by RHA) to

be satisfactory for the preliminary phase in the design of new dams and in the safety evaluation of

existing dams.

Three dams Blue stone; Folsom; and Pine Flat, were investigated by Elyas et al (2014) to identify

the effective parameters in stability of concrete gravity dams. Their study is based upon the

ABAQUS and RS-DAM software’s to observe the behavior of the sliding displacement along the

base of dam which contact the foundation. The results show that the sliding displacement has no

considerable change in each of the three nodes on heel and toe, and also in middle part of dam, and

eventually is equal in each three and all parts of the dam’s bottom and foundation.

3. Aim of the Study

The aim of current study is to check the stability of the random section of concrete dam for a wide

range of reservoir heads. Many loads are considered and critical design section with full and empty

reservoir cases is examined. The analysis is focusing on the effects of dam geometry on

requirements of safety. Mostly the change in initial dam section would be satisfied by adding a

specific amount of concrete to the upstream dam face, however, the challenge is due to the

determination of required amount which should be provided, and hence ,it may need a lot of trials

to be attained .In present study, stability analysis of concrete dam is performed over a wide range

of water heads values (starting from 40 m up to 100 m with increment of 0.5 m ), and for design

cases considering empty as well as full reservoir conditions. The analysis calculates the various




12

types of forces such as hydrostatic, uplift and seismic forces in order to determine the appropriate

increase in the dam base to ensure dam’s safety.

4. Forces acting on Concrete Dam

The following forces have been considered in analysis for both cases, empty reservoir with the

earthquake forces are act vertically upward and horizontally towards heel, and full reservoir with

earth quake forces are vertically upward and horizontally toward toe which represent the more

critical cases (Santosh 2005). These forces, shown in figure (1), are ranged in general between the

usual and extreme loads.

1. Water pressure ( ),

2. Up lift pressure ( ),

3. Pressure due to earthquake forces ( ,

4. Hydrodynamic Force ,and

5. Weight of the dam (W)

Figure 1: Forces acting on gravity dam (G.L.Asawa)

The forces can be estimated by the following equations:

The hydrostatic force can estimated from the following form:

(1)

Where:




13

Horizontal hydrostatic force, N,

Unit weight of water, ⁄ , and

Depth of water, m

The uplift force which exerted by stream lines below the dam base can be obtained by using the

formula:

(2)

Where

C: uplift pressure coefficient, and

B: Base width of dam, m.

The vertical and horizontal components of earthquake forces are function of weight of dam and can

be obtained from the following expressions:

(3)

(4)

Where

The total weight of the dam, N,

Vertical acceleration factor (mostly 0.05)

Horizontal acceleration factor (mostly 0.1)

The hydrodynamic force which represent the effect of earthquake force on reservoir it can be

obtained from one of the following expressions:

i-The Von-Karman equation:

(5)

(6)

ii- Zangar equation

(7)

Where




14

Hydrodynamic force, N

Hydrodynamic pressure,

=Moment of force about toe. And

, where Angle in degrees, which the u/s face of the dam makes with

horizontal and the moment of the force can be estimated from the equation (8)

(8)

In current study, the hydrodynamic force is assumed to be act toward the D/S of dam.

4-1 Modes of Failure of Gravity Dams

4-1-1. Overturning (rotation) about the toe.

(9)

: Anti clockwise moments, : clockwise moments

4-1-2. Crushing (compression)

(10)

Where:

=Eccentricity of resultant force from the center to the base, m,

Total vertical force, N, and

Base width, m.

4-1-3-. Development of tension, causing ultimate failure by crushing.

(11)

4-1-4. Shear failure called sliding.

F.S.S (factor of safety against sliding)

(12)

S.F.F (shear friction factor)

(13)

Where

Width of dam at the joints,m

Average strength of the joint which varies from 140 t/m2 for poor rocks, to 400 t/m

2 for good

rocks, and,




15

Friction coefficient (nearly 0.75).

4-2 Principle and Shear Stress

(14)

Where

Major principle stress which is not greater than allowable stress (f),

Minor principle stress,

= Angle which (d/s) face makes with vertical

(15)

(16)

Where

Angle which (u/s) face makes with vertical

The shear stress near toe with the case of no tail water can be obtained from the following form:

(17)

And by considering the tail water and hydrodynamic in the direction toward the u/s side, the Eq.

(19) would be change to be:

[ ] (18)

Similarly, the shear stress at heel can be expressed by the following equation:

[ ] (19)

(20)

: Centre of the base

(21)

5. Results and Discussions

In present study, all the considered forces, principal and shear stresses were estimated and

consequently, the relevant modes of failure have been checked for each specific reservoir head (H).

Many iterations of stability analysis have been carried out for both empty and full reservoir cases

up to attain the safety status. Accordingly, the width values of extra amount of concrete (b) were

obtained corresponding to each (H). Then, the relationship between the wide range of heads and

additional part of base width is presented in figure (2) in order to create an appropriate function

which it may be useful for predicting the values of additional parts of the dam base (b) required to




16

satisfy the safety conditions for each specific head (H). It can be seen from figure (2) that the

values of (b) is increased uniformly as the head in reservoir increased .The range of variation of (b)

will take more values when (H) becomes greater than (80) m. Also the fourth degree of polynomial

function can be considered as the best relation between (b) and (H) which can be used to estimate

the required values of additional base part for dam safety, Eq. (22).

Figure 2: Relation between head and base (H & b) for full reservoir

(22)

R² = 0.9769

The values and positions of eccentricity (e) are taken as main indictors for tension development

along the base of dam .As it can be seen from figure (3), that the resultant force may moves toward

toe in the case of full reservoir condition and hence the maximum stresses are created at toe and

being reduced gradually toward the heel. The minimum normal stresses at heel will either be

positive or negative. However, the values of (e) is influenced effectively by the movement of

resultant force, accordingly, if the resultant force cut the dam base outside the middle third part, the

tension will be produced on heel zone. In other words, if (e) is less than or equal to b/6, the stress

is compressive all along the base and when (e) is greater than b/6 there can be tensile stresses on

the base. In present study, the values of (e) are estimated for safe dam section and their relation

with head (H) is shown in figure (4). It can be seen from the figure that the values of (e) are

increasing when (H) is getting higher and the relation can be expressed by fourth degree

polynomial function with high value of correlation coefficient, Eq. (23).

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100

b (

m)

H (m)

b




17

Figure 3: Maximum and minimum stresses on both toe and heel of full reservoir case

Figure 4: Relation between head (H) and eccentricity (e) for full reservoir

(23)

R² = 0.9717

For the full reservoir case, if the components of earthquake forces are considered to be vertically

upward and horizontally toward D/S, the case is classified as worst case with extreme loads. The

whole forces applied on the dam lead to create the principal stresses on both upstream face rather

than downstream face in the case of tail water existing. Figure (5) shows the variation of principal

stresses ( with head of water in reservoir (H).It can be seen from the figure that the values of ( )

0

2

4

6

8

10

12

0 20 40 60 80 100

Ecce

nte

rici

ty (

e)

(m)

H (m)

e

Poly. (e)




18

are proportionally increased as (H) increased up to (H=80 m) beyond which the values of ( are

subjected to some fluctuation. Eq. (24) represents the relationship between

Figure 5: Relation between head (H) and (σ) for full reservoir

(24)

R² = 0.9881

The general behavior of eccentricity (e) with (H) in the case of empty reservoir are similar to that in

the case of full reservoir .The range of (e) values is bounded by minimum value (e=5) and

maximum value (e=9) which less than those obtained for full reservoir analysis. Figure (6) shows

the relation between (e) and (H) for case of Empty reservoir which also can be presented

mathematically by fourth degree polynomial function, Eq. (25) .

(25)

R² = 0.9973

The relation between the head (H) and both and (σ) is shown in figures (7) It can be seen from this

figures that for empty reservoir, the pattern of (σ) variation is same to that obtained from the case

of full reservoir analysis. However, the range of values is seemed to differ from the results of full

reservoir. The values of (σ) corresponding to each value of (H) can be calculated by using the

fourth polynomial equation (Eq. 26).

(26)

R² = 0.9981

0

20

40

60

80

100

120

0 20 40 60 80 100

Pri

nci

pal

Str

ess

(σ

) t/

m2

H (m)

∂ max

Poly. (∂ max)




19

Figure 6: Relation between (H & e) for empty reservoir

Figure 7: Relation between head (H) and (σ) for empty reservoir

6. Conclusions

The section of gravity dam should be chosen in such a way that it’s the most economic section and

satisfies all the conditions and requirements of stability. The higher the elevation gets the more

incensement in base required to achieve stability.

In present project, the following conclusions have been obtained:

1- That for full reservoir , the values of (b) is increased uniformly as the head in reservoir

increase .The range of variation of (b) will take more values when (H) becomes greater

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60 80 100

e (

m)

H (m)

e

Poly. (e)

0

20

40

60

80

100

120

0 20 40 60 80 100

σ

(t/m

2 )

H (m)

6max

Poly. (6max)




20

than (80) m.

2- The fourth degree of polynomial represents the best function to reflect the relation between

(b) and (H) which can be used to estimate the required values of additional base part for

dam safety.

3- For full reservoir, the values of (e) are increasing when (H) is getting higher and the

relation between these two parameters can be expressed by fourth degree of polynomial

function with high value of correlation coefficient.

4- The relation between (H & σ) for full reservoir is directly proportional and the fourth order

of polynomial function is seem to be the best representative of the relation.

5- For empty reservoir , both of (σ ) and (e) are directly proportional with (H).The range of

values are less than those obtained from the analysis of full reservoir condition .The

relations can also be expressed by fourth degree of polynomial functions with high values

of correlation coefficients.

References

Arnkjell, L. (2013). Earthquake Analysis of Concrete Gravity Dams. Master Thesis Spring,

submitted to Faculty of Engineering Science and Technology /Norwegian University of

Science and Technology.

Aryak S., Tripathi, R.K., & M. K. Verma, M.K. (2012). Safety Analysis of Rupsiabagar-

Khasiabara Dam under Seismic Condition, Using CADAM. International Journal of

Scientific and Research Publications, 2(9).

Asawa, G.L. (2008). Irrigation and Water Resources Engineering. New Delhi: New Age

International (P) Ltd., Publishers.

Elyas, B., Mansouri, A., Aminnejad, B., & Bafghi, M.A. (2014). The Investigation of Effective

Parameters on the Stability of Concrete Gravity Dams with Case Study on Folsom, Blue

Stone, and Pine Flat Dams. American Journal of Civil Engineering and Architecture, 2(5),

167-173

Hazrat Ali, M., Rabiul A. M., Naimul, H., & Alam, M.J. (2012). Comparison of Design and

Analysis of Concrete Gravity Dam. http://dx.doi.org/10.4236/nr.2012.31004.

Retrieved on 15 November, 2016 from http://www.SciRP.org/journal/nr.

Leclerc, M., Léger, P., & Tinawi, R. (2003). Computer aided stability analysis of gravity dams.

Advances in Engineering Software. Retrieved from 12 October, 2016 from

https://www.researchgate.net/publication/222211284

Santosh, K.G. (2005). Irrigation Engineering and Hydraulic Structures (19th ed.). New Delhi:

Khanna Publisher.

http://dx.doi.org/10.4236/nr.2012.31004

http://www.scirp.org/journal/nr

https://www.researchgate.net/publication/222211284




21

The Residual Strength for Different Shaped High Strength Concrete

Specimens at High Temperature

Rahel Khalid Ibrahim1 & Hiba Muhammed Muhammedemin

2

1Faculty of Engineering, Koya University, Koya, Iraq

2Near East University, Faculty of civil Engineering, Nicosia, Cyprus

Correspondence: Rahel Khalid Ibrahim Koya University, Koya, Iraq.



doi: 10.23918/eajse.2414213

Abstract: Fire can be considered as a destructive hazard that attacks concrete structures. Exposing to

high temperature causes deterioration in strength and spalling for high strength concrete members. In

this research the effect of high temperature on the different high strength concrete specimen shapes is

studied as a represent of circular and rectangular column sections. For this purpose, cube and

cylindrical shaped specimens were made from polypropylene fiber contained high strength concrete, as

well as the plain high strength concrete. After moist curing periods for 7, 28 and 90 days, the

specimens were subjected to high temperatures of 450 and 650⁰C, and their residual compressive

strength were evaluated. Cube specimens exhibited higher residual strength than cylindrical specimens

and the superior stability of rectangular section columns compared to circular ones at high

temperatures is concluded.

Keywords: High Strength Concrete, High Temperature, Polypropylene Fibers, Specimens’ Shape,

Residual Strength

1. Introduction

Controlling the sensitivity of concrete to its unstable spalling behavior during fire is one of today's

major issues in the design and construction of concrete structures. Spalling of concrete can have

serious structural and economic consequences and is a phenomenon that should be taken into

account when designing for fire since it results in crack formation and high reduction of strength.

This paper emphasizes on changing the geometrical design of column sections rather than the

material to become more stable against the exposure to high temperatures. The aim of this paper is

to compare residual strength for cube and cylindrical high strength concrete specimens to

determine the shape effect on the residual strength and the sensitivity towards spalling of high

strength concrete after exposure to fire.

2. Literature Review

Studying the fire resistance of high strength concrete (HSC) has become of a great importance in

the last years due to the high usage of this material in high-rise structures. According to the high-

rise structure designers, in the designing procedure the challenge is fire resistance. Although,

concrete has a better resistance to high temperature than the steel, still fire represents an important

threat for the damage or even collapse of many structures (Buchanan, 2002). Besides, some high

mailto:[email protected]




22

strength concrete structures like; coal gasification vessels, electrical power plants and nuclear

power plants are continuously exposed to high temperatures.

A well-hydrated cement paste generally consists of calcium silicate hydrate, calcium hydroxide and

calcium sulphate aluminate hydrate. A saturated paste also contains a large amount of free water,

capillary water and gel water (chemically bonded water). When concrete is heated to 300°C, the

free water and some of the chemically bonded water of hydration products are lost. Exposure to

500°C results in further dehydration due to the decomposition of calcium hydroxide. A complete

decomposition of calcium silicate hydrate occurs at temperatures beyond 900°C (Klieger &

Lamond, 1994). A number of studies in the same manner have shown that an increase in

temperature in cement pastes causes the release of physically absorbed water, chemically bonded

water and the decomposition of hydration products (Ye et al., 2007).

Through the increasing usage of high strength concrete in columns, fire resistance properties that

with respect to spalling have become more considerable (Caldarone, 2008). Surface spalling occurs

when a low permeable paste is subjected to a high rate of heating. This phenomenon occurs when

the vapor pressure in the pores develops stresses greater than the material’s tensile strength

(Buchanan, 2002). The internal stresses in compression members make them more vulnerable to

spalling. High strength concrete is more susceptible for spalling than the conventional concrete due

to its lower permeability. High strength concrete is of a low porosity, the interrupted moisture in

the capillary pores among the temperature rise cannot escape and result a vapor pressure in

concrete. This pressure reaches 8 MPa, almost twice the tensile strength of concrete at 300ºC

(Phan, 1997). Even if the spalling doesn’t occur the excessive vapor pressure in the system due to

high temperature causes micro-cracks which by turn leads to a significant decrease in strength

(Ibrahim et al., 2012). The strength deterioration of concrete exposed to high temperature may be

due to several factors: temperature level, rate of heating, heating time, cooling method, applied

load, type of aggregate, type of mineral admixture and air humidity (Bingöl & Gül, 2009; Khoury,

2000). Therefore, there are broadly variable results regarding the exposure of concrete to elevated

temperature (Neville, 2005). The strength deterioration for high strength concrete at elevated

temperatures is more pronounced than in normal strength concrete (Behnood & Ziari, 2008),

whereas some researchers have showed that high strength concrete performs better than normal

strength concrete at elevated temperatures (Ibrahim et al., 2011).

To overcome the spalling effect of high strength concrete it is necessary to add polypropylene

fibers to the concrete mixes. Polypropylene fibers melt at around 160ºC and become capable of

producing moisture escape channels to release the vapor pressure. Researchers showed that, 1 kg of

polypropylene fiber per one cubic meter of concrete mix is sufficient to eliminate the spalling

effect (Ibrahim et al., 2014; Kalifa et al., 2001). Many authors emphasized that, using

polypropylene fibers up to 2 kg/m3 do not have negative effect on the strength of high performance

concrete (Noumowe, Siddique, & Debicki, 2009). In this research, to alleviate the spalling effect of

the specimens, polypropylene fiber is used in amount of 1 kg/m3 for mortar and concrete mixes.

3. Materials and Methods

Portland cement, coarse aggregate, fine aggregate, super plasticizer and polypropene fiber and is

used in this research. Ordinary Portland cement type I (42.5 Mpa) obtained from Mass Company.

Fine aggregate was obtained from Bogid which has specific gravity of 2.7 and located under the

second zone. Also, Gravels having the maximum size of 12.5mm and specific gravity of 2.67




23

obtained from Bogid pit were used as a coarse aggregate. Tap water was used for mixing and

curing purposes. The superplasticizer used in this research was high performance polycarboxylic

based, under the trade name of Hyperplast PC175. The polypropylene fibers is obtained from

Timuran Engineering and holding a brand name of Fibrillated polypropylene fiber. They were

white in color, having a length of 12.19 mm with a specific gravity of 0.9 and the melting point of

160 to 170 ºC. The tensile strength for the fibers was 0.36 kN/mm2. The material was used for

those specimens that were subjected to high temperatures. The recommended dosage of material

usage is 1 to 2 Kg/m3 of concrete.

A concrete mixture containing 1Kg polypropylene fiber per one cubic meter of concrete was

prepared beside the control mixture. The water cement ratio for all mixtures were fixed to (0.38), to

keep this rate constant super plasticizer was used for attaining proper workability. The mix

proportion for 1m3 of concrete is shown in the Table 1.

From each concrete mix 27, (100*100*100mm) cubes and 27 (100*200mm) cylinders were casted.

The cube and cylinder specimens where put in water for 7, 28 and 90 days as a moist curing. From

each concrete mixture and curing regime at least 3 cubes and 3 cylinders were taken out from

water, surface dried and exposed to high temperatures of and for hrs at a heating rate of

9°C/min. The heated specimens were cooled to room temperature and subjected compression test

beside the controlled non heated specimens. The compression test was performed according to

(EN, 2009) and (ASTM, 2015) standards of compression test for cubes and cylinders respectively.

Table 1: The Mix Proportions per One-Meter Cube of Concrete

Flow

mm

Slump

mm

Polypropylene

Fiber

Kg/m3

Super

plasticizer

Kg.

Alum

sludge

Kg.

Water

Kg.

Sand

Kg.

Gravel

Kg.

Cement

Kg.

Mix

Code

550 240 0 5 0 180 870 930 480 P

550 240 1 5.5 0 180 870 930 480 PP

4. Results and Discussion

4.1 Compressive Strength before Exposure to High Temperature

Table 2 shows the compressive strength results for P (cubes), PP (cubes containing polypropylene

fiber), C (cylinders) and CP (cylinders containing polypropylene fiber) 7, 28 and 90 days

respectively before and after exposure to high temperature. It can be observed that cub specimens

shows higher strength than the cylinder ones for all curing periods. A compressive strength of

56.68 MPa was recorded for 28 day cube specimens, While, cylinder specimens had 54.89 MPa

compressive strength. From these results the produced concrete can be categorized under high

strength concrete. Both cube and cylinder specimens exhibited gradual increase in strength by

increasing the moist curing periods

Maximum compressive strength of 59.55 MPa and 55.18 MPa was recorded for 90 days from cured

cube and cylinder specimens respectively. The incorporation of polypropylene resulted in a slight

decrease in strength for both cube and cylinder specimens for all curing periods.




24

Table 2: Compressive Strength for Different Curing Regimes and Different Exposure Temperatures

(MPa)

Specimens

Compressive strength for different curing regimes and different exposure

temperatures (MPa)

7 Days 28 Days 90 Days

26⁰C

450⁰

C

650⁰

C 26⁰C 450⁰C 650⁰C 26⁰C 450⁰C 650⁰C

P 50.09 39.06 20.44 56.68 48.47 26.61 59.55 48.05 29.29

PP 46.82 35.37 17.48 51.44 48.45 26.59 56.29 49.04 30.03

C 45.16 22.27 10.48 54.89 32.13 14.79 55.18 32.79 16.50

CP 41.22 23.71 12.95 48.94 35.60 16.44 52.68 37.26 18.34

4.2 Compressive Strength After 450⁰C

The exposure to 450⁰C resulted in a decrease in compressive strength for both cube and cylinder

specimens with respect to non-heated specimens. Cube specimens showed superior residual

compressive strength than cylinder ones in both polypropylenes contained and non-polypropylene

contained specimens for all curing periods.

The incorporation of polypropylene fibers resulted in enhances of residual strength for both cube

and cylinder specimens with respect to non-polypropylene contained specimens for all curing

regimes. The effect of polypropylene fibers on the residual strength of cylinders is more

pronounced than cubes. Polypropylene fibers melt at 200⁰C, so they provide open channels for the

vapor pressure to release; hence reducing the micro cracks an increasing the residual compressive

strength. The incorporation of polypropylene fibers enhanced the residual strength for cylinders by

nearly 2 MPa with respect to non-polypropylene contained cylinders. Maximum residual

compressive strength of 49.04 MPa was recorded for 90 day from cured polypropylene contained

cube specimens.

4.3 Compressive Strength After 650⁰C

The exposure of the specimens to 650⁰C resulted in a dramatic decrease in compressive strength.

Once again, cube specimens showed superior residual strength than cylinder specimens. The higher

residual strength for cube specimens than the cylinder ones is most probably due to that the shape

of cubes provides shorter escape path for vapor to escape than the cylinder specimens due to higher

surface area of cubes. The incorporation of polypropylene fibers enhanced the residual strength for

cylinders by nearly 2MPa with respect to non-polypropylene contained cylinders. Maximum

residual compressive strength of 30 MPa was recorded for 90 day cured polypropylene contained

cube specimens.

4.4 Visual Inspections

Some non-polypropylene contained cylinder specimens spalled explosively after exposure to

450⁰C (Fig.1) while, no spalling were observed for non-propylene contained cube specimens. This

phenomenon is due the excessive build up vapor pressure generated in cylinder specimens with

compared to cube ones, which can be explained by higher surface area of cubes that provides more




25

vapor release than in cylinders. No spalling was occurred in cylinder and cube specimens when

polypropylene fibers were added to the concrete mix.

Figure 1: Spaling of cylinder specimens after exposure to 450⁰C.

Figure 2 shows the change in color for non-polypropylene (P) and polypropylene (CP)

contained cylinder specimens before and after exposure to high temperatures. The green color

of concrete at 26⁰C turns to light grey after exposure to 450⁰C and the color becomes even

lighter after exposure to 650⁰C due to the decomposition of hydration products to lime which

have a lighter color. Cracks can be seen on the specimens surface after exposure to 650⁰C.

Figure 2: Non-polypropylene (P) and propylene (CP) contained cylinder specimens after exposure

to different temperatures

650⁰C

450⁰C

26⁰C




26

The images of non-polypropylene (P) and polypropylene (PP) cube specimens after exposure to

different temperatures are shown in figures 3 and 4 respectively. The higher the exposure

temperature the lighter the color of the specimens becomes. The exposure to 650⁰C induced in

visual cracks on the specimens’ surface

Figure 3: Non-polypropylene contained cube specimens after exposure to different

temperatures

Figure 4: Polypropylene contained cube specimens after exposure to different temperatures

5. Conclusions

From this research the following conclusions can be drawn:

It is possible to produce high strength concrete having 90 day compressive strengths up to

59.55 MPa for cubes and 55.18 MPa for cylinders.

Maximum residual compressive strength of 49.04 MPa was recorded for 90 day cured

polypropylene contained cube specimens after exposure to 450⁰C

Maximum residual compressive strength of 30 MPa was recorded for 90 day cured

26⁰C

450⁰C

650⁰C

26⁰C

450⁰C

650⁰C




27

polypropylene contained cube specimens after exposure to 650⁰C.

The incorporation of polypropylene fibers enhances the residual strength for both cube and

cylinder specimens after exposure to high temperature.

The rectangular sections are more resistible to the exposure to high temperature than the

circular ones.

The exposure to 650⁰C induced in visual cracks on concrete surface.

Acknowledgment

The authors highly appreciate the research center of faculty of engineering at Koya University for

their technical support in performing the experimental part for this research.

References

ASTM. (2015). C39 / C39M - 15a Standard Test Method for Compressive Strength of Cylindrical

Concrete Specimens. West Conshohocken, PA: ASTM International.

Behnood, A., & Ziari, H. (2008). Effects of silica fume addition and water to cement ratio on the

properties of high-strength concrete after exposure to high temperatures. Cement and

Concrete Composites, 30(2), 106-112.

Bingöl, A. F., & Gül, R. (2009). Effect of elevated temperatures and cooling regimes on normal

strength concrete. Fire and Materials, 33(2), 79-88.

Buchanan, A. (2002). Structural Design for fire Safety. UK: Wiley Chichester.

Caldarone, M. (2008). High-Strength Concrete: A Practical Guide: Taylor & Francis Group.

EN, B. (2009). BS EN 12390-3:2009 Testing Hardened Concrete. Compressive Strength of Test

Specimens. London, UK: British Standards Institution.

Ibrahim, R. K., Hamid, R., & Taha, M. (2012). Fire resistance of high-volume fly ash mortars with

nanosilica addition. Construction and Building Materials, 36, 779-786.

Ibrahim, R. K., Hamid, R., & Taha, M. (2014). Strength and Microstructure of Mortar Containing

Nanosilica at High Temperature. ACI Materials Journal, 111(2).

Ibrahim, R. K., Ramyar, K., Hamid, R., & Raihan Tah, M. (2011). The effect of high temperature

on Mortars containing silica fume. Journal of Applied Sciences, 11, 2666-2669.

Kalifa, P., Chene, G., & Galle, C. (2001). High-temperature behaviour of HPC with polypropylene

fibres:: From spalling to microstructure. Cement and Concrete Research, 31(10), 1487-

1499.

Khoury, G. A. (2000). Effect of fire on concrete and concrete structures. Progress in Structural

Engineering and Materials, 2(4), 429-447.

Klieger, P., & Lamond, J. (1994). Significance of tests and properties of concrete and concrete-

making materials: ASTM International.

Neville, A. M. (2005). Properties of Concrete: Pearson

Noumowe, A. N., Siddique, R., & Debicki, G. (2009). Permeability of high-performance concrete

subjected to elevated temperature (600 C). Construction and Building Materials, 23(5),

1855-1861.

Phan, L. T. (1997). International Workshop on Fire Performance of High-Strength Concrete:

NIST, Gaithersburg, MD, February 13-14, 1997: US Department of Commerce,

Technology Administration, National Institute of Standards and Technology.

Ye, G., Liu, X., De Schutter, G., Taerwe, L., & Vandevelde, P. (2007). Phase distribution and

microstructural changes of self-compacting cement paste at elevated temperature. Cement

and Concrete Research, 37(6), 978-987.




28

Assessment of Strengthening Scheme of Existing Buildings Extended by

Adding Additional Floors

Bayan S. Al-Nu’man

1

1 Civil Engineering Department, Faculty of Engineering, Ishik University, Erbil, Iraq

Correspondence: Bayan Al-Nu’man, Ishik University, Erbil, Iraq.



doi: 10.23918/eajse.2414214

Abstract: This study intends to analyze and design existing RC frames, of different concrete

compressive strengths when extended by adding more floors to the existing buildings. It may be

decided whether a strengthening scheme is feasible or not.

In this work, analyses are made of 3 buildings of 14-stories with different compressive strengths in the

first 6-floor columns for each building, extended to 16-stories frame by adding 2 stories of Normal

weight concrete (NWC) or Steel.

A case study is selected which is an existing RC buildings, and the owner requested 2 additional floors.

It is assumed that the foundation system is capable of carrying the additional floors. First the capacity

of the superstructures must be known, by using data obtained from the previous designs of the existing

buildings.

After extending the building by NWC or Steel, by using STAAD-pro, it has been shown that a

considerable portion of the total number of columns in the superstructure of the existing building

couldn’t carry the new loads due to the additional 2 floors, so in order to add two additional floors,

strengthening scheme must be planned for the columns which require additional capacity.

Keywords: Existing Building, Additional Floor, Strengthen

1. Introduction

The extension of (adding stories to) existing buildings is required in development of urban

construction all over the world. With the increase of population, cities are bound to expand but

actual area of individual city is limited. It is therefore necessary to confine the development within

the scope of the city properly. This requires raising the height of buildings in the city, especially

where existing buildings are very low in height.

There are some solutions to this issue:

1. Demolishing the existing building and construct new high rise building at the site. But it will

cause problem of moving people to other place, cost of demolishing, and the disposal of waste

from the construction site despite of these problems there are some buildings are demolished

without reaching their service life.

2. Raising the height of the existing buildings. This comprises mainly in the following process:

a. The existing building has capacity to carry the extension of building, which means the




29

weight additional floors are to be supported by the existing building structure. However

the capacity of the existing building is limited, only one or two floors can be added at

most.

b. If the foundation could carry the extension but the super structure couldn’t then one of

these strengthening methods shall be planned to increase the capacity of super structure.

c. The extension is done by means of pure frame: the weight of additional floors can’t be

transmitted by the super-structure to the foundation, because the existing structure has not

taken into consideration that the building will be extended.

d. Anchoring the new additional frame to the existing frame should be securely executed

(Slao, 1994).

2. Objective

The objectives of this study are to generate structural design and techniques to be used when

adding more floors on existing buildings without demolishing the existing buildings by using a case

study of residential reinforced concrete buildings. Different concrete compressive strengths are

used to study their effects. Furthermore, this research also intends to develop possibility of using

lightweight materials (Steel), as a solution for additional stories on existing buildings.

3. Analyses of the Case Study

The case study consists of 3 residential reinforced concrete buildings of 14 floors. In the first

building the overall compressive strength of 28 MPa is used, in the second and third buildings the

first 6 floor columns are of high strength concrete (ACI, 2010); 56 MPa and of 84MPa compressive

strength, respectively, with the remaining columns of 28 MPa.

The owner wants to add two more floors; 16-floor building rather than 14-.

There are two solutions of providing these additional floors to the existing buildings; first one is

demolishing the existing building and constructing a new one, and the second is adding floors on

the existing buildings.

The second option will be selected.

The major problem is to know if the old buildings can support the new one or look for other

structural solutions.

It is assumed that the foundations are fixed and can support the extension loading safely, then only

the super structure behavior of the existing buildings is a key factor to know whether the new and

the old structures can be integrated or not. Surely, the existing roof floor systems are now an

intermediate floor in the extended building. When two floors are added, a live load of 5 kN/m2

is

used for these floors, so any measure of strengthening if required for the slab is assumed taken.

Steel or Normal Weight Concrete is used in the extension part of the existing buildings.

In the beginning of the work, the area of steel for each member of the existing buildings will be

taken from the previously designed plans.




30

Due to adding two floors to the existing building, strengthening schemes of the existing super

structures are required.

4. Structural Information about the Case Study

All beams and columns dimensions are given below:

-Beam section dimension 400 mm wide by 600 mm deep.

-Interior Column section dimension from 1st up to 6th floor is 800 mm by 800 mm, from 7

th up to 11

th floor

is 600 mm by 600 mm, and from 12th up to 14

th+15

thand 16

thfloor is 400 mm by400 mm.

-Exterior Column dimensions from 1st up to 11th floor is 600 mm by 600 mm, and from 12

th up to

14th+15

thand 16

th floor is 400*400 mm

Thickness of the slab is 200 mm

Thickness of slab for composite floor system = 100mm

Height of each story 3 m, except for ground floor the height is 4 m

Concrete strengths are f’c= 28 , 56, and 84 MPa.

Steel yield strength fy = 420 MPa

Density of concrete= 24 kN/m3

Density of light weight concrete (used for the floor system of Steel) = 18 kN/m3

Minimum concrete cover for the reinforcement for beams and columns = 40 mm

Steel sections yield strength, fy = 345 MPa, and maximum tensile strength fu = 450 MPa

In this work, theoretical investigation of the moment, shear, and axial forces are conducted by using

computer program (STAAD Pro 2007 V8i). A typical floor of the studied building consists of 4 bays of

spans 7 m, 5.2 m, 5.2 m and 7 m center-to-center in each direction. Design of sections follows ACI 318 –

14 code (ACI, 2014).

5. Results

Results of required reinforcement ratio (%), before adding the new floors, are listed in tables (1)

and (2), and figures (1) and (2), for selected interior and edge columns, respectively, in each floor

corresponding to different concrete strengths. Note the ground floor columns’ greater requirement

and at the 6th floor when column sizes are reduced. A minimum ratio is 1% according to ACI code.

(4) However, when strength is increased to 56 or 84 MPa, only the minimum reinforcement ratio is

required in the ground floor columns.

Tables (3) to (8) and figures (3) to (8) show the variation of steel requirements after extension of

two additional floors, corresponding to variations in concrete strengths from 28 to 56 to 84 MPa,

for typical interior and edge columns.

9 out of 14 (9 / 14) interior columns require strengthening using 28 MPa, corresponding to (5 / 14)

using 56 MPa, and 84 MPa concrete strength. The respective numbers are (8/14), (3/14) for edge

columns.




31

Table 1: Reinforcement percentage with different concrete strengths f’c before extension, for

selected interior columns

Interior columns Fc'

28 56 84

floor(s) Col. No. Dim(mm) As%

Ground 83 800*800 3.37 1 1

1st 176 800*800 2.76 1 1

2nd 269 800*800 1 1 1

3rd 362 800*800 1 1 1

4th 455 800*800 1 1 1

5th 548 800*800 1 1 1

6th 641 600*600 3.27 3.27 3.27

7th 734 600*600 1 1 1

8th 827 600*600 1 1 1

9th 920 600*600 1 1 1

10th 1013 600*600 1 1 1

11th 1106 400*400 1 1 1

12th 1199 400*400 1 1 1

13th 1292 400*400 1 1 1

Figure 1: Effect of concrete strength on steel ratio for a typical interior columns before

extension




32

Table 2: Reinforcement percentage with different concrete strengths f’c before extension, for

typical edge columns

Edge columns Fc'

28 56 84

floor(s) Col. No. Dim(mm) As%

Ground 90 600*600 4.18 1 1

1st 183 600*600 3.57 1 1

2nd 276 600*600 2.68 1 1

3rd 369 600*600 1 1 1

4th 462 600*600 1 1 1

5th 555 600*600 1 1 1

6th 648 600*600 1 1 1

7th 741 600*600 1 1 1

8th 834 600*600 1 1 1

9th 927 600*600 1 1 1

10th 1020 600*600 1 1 1

11th 1113 400*400 1 1 1

12th 1206 400*400 1 1 1

13th 1299 400*400 1.69 1.69 1.69

Figure 2: Effect of concrete strength on steel ratio for a typical edge columns before extension




33

Table 3: Reinforcement percentage variation before and after extension and strengthening

requirement for typical interior columns, for concrete strength f’c = 28 MPa

Typical Interior columns F’c=28 MPa

floor(s) Col. No. Dim(mm) Existing

building

Extension

with NWC

Extension

with Steel

Strengthening

Ground 83 800*800 3.37 4.71 4.71 Required

1st 176 800*800 2.76 3.92 3.68 Required

2nd 269 800*800 1 3.14 3.01 Required

3rd 362 800*800 1 2.45 2.16 Required

4th 455 800*800 1 1 1 Not required

5th 548 800*800 1 1 1 Not required

6th 641 600*600 3.27 5.36 5.36 Required

7th 734 600*600 1 4.18 3.81 Required

8th 827 600*600 1 3.27 2.68 Required

9th 920 600*600 1 1 1 Not required

10th 1013 600*600 1 1 1 Not required

11th 1106 400*400 1 6.03 6.03 Required

12th 1199 400*400 1 3.68 3.14 Required

13th 1292 400*400 1 1 1 Not required

14th 1385 400*400 - 1 - -

15th 1478 400*400 - 1 - -

Figure 3: Variation of steel ratio after extension for interior columns, for f’c =28MPa




34





building

Extension

with NWC

Extension

with Steel

Strengthening

Ground 83 800*800 1 1.22 1 Required

1st 176 800*800 1 1 1 Not required

2nd 269 800*800 1 1 1 Not required

3rd 362 800*800 1 1 1 Not required

4th 455 800*800 1 1 1 Not required

5th 548 800*800 1 1 1 Not required

6th 641 600*600 3.27 5.36 5.36 Required

7th 734 600*600 1 4.18 3.81 Required

8th 827 600*600 1 3.27 2.68 Required

9th 920 600*600 1 1 1 Not required

10th 1013 600*600 1 1 1 Not required

11th 1106 400*400 1 6.03 6.03 Required

12th 1199 400*400 1 3.68 3.14 Required

13th 1292 400*400 1 1 1 Not required

14th 1385 400*400 - 1 - -

15th 1478 400*400 - 1 - -





35





building

Extension

with NWC

Extension

with Steel

Strengthenin

g

Ground 83 800*800 1 1 1 Not required

1st 176 800*800 1 1 1 Not required

2nd 269 800*800 1 1 1 Not required

3rd 362 800*800 1 1 1 Not required

4th 455 800*800 1 1 1 Not required

5th 548 800*800 1 1 1 Not required

6th 641 600*600 3.27 5.36 5.36 Required

7th 734 600*600 1 4.18 3.81 Required

8th 827 600*600 1 3.27 2.68 Required

9th 920 600*600 1 1 1 Not required

10th 1013 600*600 1 1 1 Not required

11th 1106 400*400 1 6.03 6.03 Required

12th 1199 400*400 1 3.68 3.14 Required

13th 1292 400*400 1 1

1

Not

required

14th 1385 400*400 - 1 - -

15th 1478 400*400 - 1 - -





36


requirement for typical edge columns, for concrete strength f’c = 28 MPa

Typical Edge columns F’c=28MPa


building

Extension

with NWC

Extension

with

Steel

Strengthening

Ground 90 600*600 4.18 6.54 5.36 Required

1st 183 600*600 3.57 5.36 4.46 Required

2nd 276 600*600 2.68 4.18 3.81 Required

3rd 369 600*600 1 3.57 3.27 Required

4th 462 600*600 1 2.68 2.18 Required

5th 555 600*600 1 1 1 Not required

6th 648 600*600 1 1 1 Not required

7th 741 600*600 1 1 1 Not required

8th 834 600*600 1 1 1 Not required

9th 927 600*600 1 1 1 Not required

10th 1020 600*600 1 1 1 Not required

11th 1113 400*400 1 3.14 2.01 Required

12th 1206 400*400 1 2.01 1.57 Required

13th 1299 400*400 1.69 1.22 3.14 1 Required

14th 1392 400*400 - 1.22 - -

15th 1485 400*400 - 2.35 - -

(1) In the 14

th floor, all the moments are transferred to the column below, that’s why the percentage

of two additional floors is more than the NWC.

(*2) Reduction of the cross section size is made at 11th floor, so sudden change of reinforcement is

occurred.

Same notes are valid for figures (7) and (8).

Figure 6: Variation of steel ratio after extension for edge columns, for f’c =28MPa




37



Typical Edge columns F’c = 56 MPa


building

Extension

with NWC

Extension

with Steel

Strengthening

Ground 90 600*600 1 1.25 1 Required

1st 183 600*600 1 1.63 1 Required

2nd 276 600*600 1 1 1 Not required

3rd 369 600*600 1 1 1 Not required

4th 462 600*600 1 1 1 Not required

5th 555 600*600 1 1 1 Not required

6th 648 600*600 1 1 1 Not required

7th 741 600*600 1 1 1 Not required

8th 834 600*600 1 1 1 Not required

9th 927 600*600 1 1 1 Not required

10th 1020 600*600 1 1 1 Not required

11th 1113 400*400 1 3.14 2.01 Required

12th 1206 400*400 1 2.01 1.57 Required

13th 1299 400*400 1.69 1.22 3.14 1 Required

14th 1392 400*400 - 1.22 - -

15th 1485 400*400 - 2.35 - -





38




Typical Edge columns F’c = 84 MPa


building

Extension

with NWC

Extension

with Steel

Strengthening

Ground 90 600*600 1 1 1 Not required

1st 183 600*600 1 1 1 Not required

2nd 276 600*600 1 1 1 Not required

3rd 369 600*600 1 1 1 Not required

4th 462 600*600 1 1 1 Not required

5th 555 600*600 1 1 1 Not required

6th 648 600*600 1 1 1 Not required

7th 741 600*600 1 1 1 Not required

8th 834 600*600 1 1 1 Not required

9th 927 600*600 1 1 1 Not required

10th 1020 600*600 1 1 1 Not required

11th 1113 400*400 1 3.14 2.01 Required

12th 1206 400*400 1 2.01 1.57 Required

13th 1299 400*400 1.69 1.22 3.141 Required

14th 1392 400*400 - 1.22 - -

15th 1485 400*400 - 2.35 - -




39

6. Discussions and conclusions

6.1 Effect of Varying Concrete Compressive Strength on Reinforcement Ratio of Columns of

Existing Building before Extension

1. When strength f’c = 56 MPa is used for the first six floor columns, all the percentage of columns

were changed, except the columns which minimum reinforcement were used, however, there

weren’t any significance change between (84 and 56) MPa in the reinforcement percentage,

since most of the columns were designed according to the minimum reinforcement in columns

(1%), so it is better to use smaller cross sections in columns when high strength concrete is used

2. There weren’t any change for the columns from 6th floor to 13

th floor since they have the same

f’c of 28 MPa.

6.2 Investigation of Existing Buildings after Extension

1. Strengthening scheme of existing buildings are required, since some of the columns couldn’t

carry the additional load of the extensions for the studied existing buildings of 14-floors when

2 additional floors of Steel or NWC added to the old buildings. Normally wind loads were

taken into account and it didn’t change the results significantly after extensions.

2. When NWC is used for the extension of existing building with column f’c = 28 MPa, the

percentage of existing columns need to be strengthened is (146/490=29.8%). When Steel is

used for the extension, the percentage is (141/490= 28.7%).


percentage of existing columns need to be strengthened is (85/490 = 17.3%). When Steel is

used for the extension, the percentage is (81/490 = 16.5%).


percentage of existing columns need to be strengthened is (69/490 = 14%). When Steel is used

for the extension, the same percentage is obtained (69/490 = 14%).

5. However, for Steel, the strengthening scheme is less intensive than that for the NWC, since the

additional strength required is much less. In some cases, the same percentage is found for both

NWC and Steel. This is because what is shown is the provided percentage. In fact, the

analytical required is less, but it is rounded up for the practical reasons. The higher value of f’c

was used, the less number of columns needed to be strengthened.

6. Interior columns are more affected by the extension than the edge columns, for example for

existing building with f’c= 28 MPa; the percentage of interior columns need to be strengthened

is 16.9% while for edge columns are 11.83% when Steel is used. For NWC the percentage of

interior columns need to be strengthened is 17.95% while for edge columns are 11.83%.

7. The greatest critical difference detected was in edge column (no. 183), approximately 6.03% of

reinforcement required for existing column with 1.69% of steel percentage, therefore special

strengthening scheme is recommended.

8. As expected, the upper floor corner columns of existing building had shown improvement in

strength after extension by NWC. The additional compression (larger axial load) will reduce

the tensile stress in steel in the tension zone (Nilson, 2012; Wright & MacGregor 2012).




40

References

Siao, W.B. (1994). Reinforced Concrete Column Strength at Beam/Slab and Column Intersection.

ACI Str. Journal, 91(1), 3-9.

ACI Committee 363. (2010). 363R -10 Report on High Strength Concrete, ACI 363 R-10, Detroit:

American Concrete Institute.

Technical reference manual STAAD Pro 2007 V8i, Bentley system, 572p.

ACI Committee 318. (2014). Building Code Requirements for Reinforced Concrete, ACI 318-14,

Detroit: American Concrete Institute.

Nilson AH, Darwin D, Dolan CW. (2010). Design of Concrete Structures (Fourteenth

Edition). New York: The McGraw Hill Companies.

Wight, J. K., & MacGregor, J. (2012). Reinforced Concrete, Mechanics and Design (6th Edition).

New York: Pearson.




41

The Critical Links between Socio-Demographic Dynamics of Sundarbans

Impact Zone and Forest Resource Depletion, Bangladesh: A Review

Sanaul Haque Mondal1

1Department of Social Relations, East West University, Dhaka, Bangladesh

Correspondence: Sanaul Haque Mondal, East West University, Dhaka, Bangladesh.


Received: September 14, 2016 Accepted: October 29, 2016 Online Published: December 1, 2016

doi: 10.23918/eajse.2415215

Abstract: The question often asked is, does population dynamics in Sundarbans Impact Zone (SIZ)

matters to degradation of Sundarbans Reserve Forest in Bangladesh? This study aims to examine the

link whether population factors contribute to degradation of Sundarbans or not. Population size of SIZ

increased by around 56% in 2011 compared with 1974 (from 1377763 in 1974 to 2155889 in 2011).

Annual population growth rate in SIZ districts decreased dramatically, but sheer number of

population increased significantly which had contributed to increase the overall population size.

During 2001 and 2011, population growth rate of SIZ area was negative, yet the forest land decreased

which could be explained by the impact of climate change. Hence, not only population factors but also

other mediating factors are interplaying to the depletion of resources from Sundarbans. Rigorous

study on demographic determinants of SIZ is required while formulation policies and programs at

micro and macro level.

Keywords: Sundarbans Impact Zone (SIZ), Population Dynamics, Resource Depletion, Mangrove

Forest, Bangladesh

1. Introduction

With 11% forest area (World Bank), Bangladesh is the 8th most populous country (Population

Reference Bureau) of the world. According to 2011 Census, the total population of Bangladesh was

14, 97, 72, 364 with a density of 1015 person per square kilometer. And the density of population

in 2011 almost doubled compared to 1974. Conversely, forest cover decreased between 1983 and

1995 at an average annual rate of 0.12%, and average stand density of the forest reduced by 87%

between 1933 and 1995 (Sen, 2010). The heavy population pressure is placing growing demand on

natural resources, especially forest sector. Over one million people directly or indirectly depend on

the forest for their livelihood and the forest contributes great amount of Gross Domestic Product

(GDP) in Bangladesh (Giri et al., 2008). About 2% of the labor force of the country was engaged in

the forestry sector, contributed about 2% of total GDP of Bangladesh (BBS, 2014). The per capita

forest land in Bangladesh has been decreasing at an alarming rate. At approximately 0.02 ha per

person of forest, Bangladesh currently has one of the lowest per capita forest ratio in the world

(Zaman, 2011). Most of the forest cover has distributed sparsely over the country.

mailto:[email protected]




42

Bangladesh has shared the world‟s largest mangrove forest with India. Since 1947 the Sundarbans

mangroves are divided between India and Bangladesh (erstwhile East Pakistan), as Sundarbans in

Bangladesh (also known as Sundarbans Reserve Forest, SRF) and as Sundarbans National Park in

India (Rahman, 2007). The Sundarbans Mangrove Forest (SMF) extends over the South-west part

of Bangladesh (Bagerhat, Satkhira and Khulna district of Bangladesh) and the Southeastern part of

the State of West Bengal in India. The SRF is located at the southern edge of the Gangetic delta

bordering the Bay of Bengal and is bounded by the Baleswar River on the east and Harinbanga

River (international boundary with India) on the West. The SRF covers an area of 6,017 square

kilometer which accounts for 4.07% of total area of Bangladesh and 40% of total area managed by

the Forest Department (BBS, 2014). Sundarbans is the single largest source of forest resources in

the country. Around 2 million people of the Sundarbans Impact Zone (SIZ) directly and indirectly

depend on Sundarbans and its resources. Among them several thousands of frontier populations are

directly engaged in Sundarbans resource extracting for their livelihoods. These people enter into

the forest to catch fish fry, collect honey, wood resources and other economic purposes.

Consequently, demographic variables are very important for population- environment study. The

forest is very important for its protective and productive functions. The role of Sundarbans in

environmental process is noteworthy. It plays as a buffer in protecting the densely populated areas

from the aggression of frequent cyclones, storm surges and tidal waves. It is the most economically

valuable and the richest natural forests of Bangladesh. Over 0.1 million people work as primary

collectors of forest products in Sundarbans (Choudhury & Hossain, 2011). Sundarbans contributes

about 41% of the total forest revenue (Shah, 2010). The Sundarbans is free from any encroachment

and permanent human habitation except few hundreds of Forest Department personnel on official

duty.

2. Aims and Methodology

This research work intended to examine the link, whether population factors contribute to

degradation of Sundarbans or not. To arrest the critical link this study examined the socio-

demographic dynamics of SIZ from 1974 to 2011 (census years) and role of population dynamics

to the depletion of Sundarbans resources.

This study combined socio-demographic dynamics of SIZ and depletion of resources from

Sundarbans reserved forest. Data were collected from published census reports of Bangladesh

Bureau of Statistics (BBS) and other secondary literatures. These included researches and data sets

from Bangladesh Bureau of Statistics (BBS), United Nations, World Bank, Integrated Protected

Area Co-Management (IPAC), NGO publications, newspapers, etc. and researches carried out by

scholars (books, journals, etc.). Population data were collected from BBS population censuses

reports for 1974, 1981, 1991, 2001 and 2011. The same data were analyzed to establish changes in

population size, age structure and sex composition through time. Changes in population in terms of

size, age structure and sex composition for 1974, 1981, 1991, 2001 and 2011 were analyzed to

determine trends and changes in population characteristics to compare such changes with changes

in forest cover. Statistical tables and graphs were generated using Microsoft Office Excel package.

3. Study Area

The periphery of the SRF includes the legally declared “Ecologically Critical Area” assumed to be




43

within a 20 km band surrounding the SRF. This is what can be called the Sundarbans Impact Zone

(Islam, 2010). The SIZ comprises 5 districts (Bagerhat, Khulna, Satkhira, Pirojpur and Barguna),

10 upazilas (Sadar, Mongla, Morrelganj, Sarankhola; Dacope, Koyra, Paikgacha; Shymnagar;

Mathbaria; and Patharghata), 151 unions/wards and 1,302 villages (Islam, 2010). This study

considered population dynamics of SIZ at upazila (sub-district) and district level.

Figure 1: Map of study area

4. Results

4.1. Socio-Demographic Dynamics of SIZ

4.1.1. Population Size and Distribution

SIZ districts had a population of 7.8 million which constituted about 5.4% of country‟s population

(BBS, 2011). Among the SIZ districts, the highest percentage of population was settled in Bagerhat

SIZ (53.3%), followed by Khulna (25.6%), Pirojpur (23.6%), Barguna (18.36%) and the lowest in

Satkhira SIZ (16.0%). Around 2.2 million people inhabited in the SIZ upazila which was around

1.5% of the country‟s total population and around 32% of the SIZ districts (BBS, 2011).

The demographic trends for Bangladesh revealed that the population became almost doubled

between 1974 and 2011 (from 76 million in 1974 to 144 million in 2011). This data also

demonstrated that at national level, population increased by about 60% during 1981 to 2011 (from

90 million in 1981 to 144 million in 2011), while at the same period population increased by 28%

in Bagerhat (from 208143 to 266389) and Sarankhola (from 92734 to 119084), 40% in Mongla

(from 97399 to 136588), 8% in Morrelganj (from 272112 to 294576), 36% in Shyamnagar (from

234164 to 318254), 55% in Koyra (from 125090 to 193931), 31% in Dacope (from 116455 to

152316) and 41% in Paikgachha (from 175715 to 247983). This analysis suggested that population




44

growth (in percentage) of SIZ upazilas did not crossed the national growth.

Although the absolute number of population during 1974 to 2011 increased, the percentage of

population shared by SIZ upazila to the country‟s total population decreased during the same

period. Moreover, the actual size of population decreased in 2011 compared to 2001 census.

Figure 2: Percentage of population shared by each upazila

4.1.2. Annual Population Growth Rate

At national level, the annual population growth rate was positive in 2001 and 2011, but negative

growth was observed in Mongla, Dacope, Paikgachha and Mathbaria upazila suggesting absolute

decrease in population size. While other SIZ upazilas observed positive growth with colossal

fluctuations.

Figure 3: Annual population growth rate of SIZ upazila

SIZ districts experienced a dramatic decline in growth rate. The highest growth rate was found in

Khulna (5.12%) district in 1974, while this district observed negative growth rate (-0.25%) in 2011.

In 1974, almost similar growth rate observed for Bangladesh (2.48%) as a whole and Bagerhat

(2.62%), but after four decades (in 2011) Bagerhat (-0.47%) showed negative growth rate. The




45

similar declining tendency found for Satkhira, Pirojpur and Barguna district. Differences in growth

rate were mainly caused by variations in the rates of internal migration. Probably these factors also

influenced by climatic abnormalities in coastal zones.

Table 1: SIZ district wise population growth rate from 1974- 2011

Source: Compile from different censuses of BBS (1974, 1981, 1991, 2001 and 2011)

4.1.3. Household and Household Size

For forested areas, households are an important demographic variable in determining the

dependency on forest resources. In the frontier forest area, most of the households have a

profession which is related to forest. The extent of forest resource dependency depends on

household size, the number of households and the materials used to build homes.

During 1974 to 2011, the number of households increased in all SIZ upazilas. The number of

households in Sarankhola (from 12680 to 64022), Mongla (from 11058 to 32383), Shyamnagar

(from 33209 to 72279), Koyra (from 19524 in 1981 to 45750 in 2011) and Dacope (from 16846 to

36597) upazila crossed doubled figures during that time. In 2011, number of people per household

in SIZ upazilas was within 3.8- 4.24 that was dismounted from around 6 in 1981. The average

household size of SIZ upazila was below the national average (4.44 in 2011) size.

4.1.4. Population Density

Population density in SIZ districts (556 persons/ km2) and SIZ upazilas (425.5 persons/ km

2) were

below national average (976 persons/ km2) in 2011. While the population density at national level

increased by about 84% in 2011 from 1974, some SIZ districts like Bagerhat (44%) recorded the

lowest increase in population densities followed by Khulna (68%) and Satkhira (76%). It is worthy

to mention that population densities decreased remarkably in some SIZ upazilas like Mongla (8.8%

from 102 to 93 persons/ km2), Morrelganj (15.7%, from 758 to 639 persons/ km

2) and Dacope

(3.1%, from 159 to 154 persons/ km2) during 2001 to 2011 period. Such decreased in population

densities also observed for Bagerhat (4.6%, from 391 to 373 persons/ km2) and Khulna (2.4%, from

541 to 528 persons/ km2) districts. Probably, this decrease in population densities was due to

landfall of two devastating cyclones namely Sidr (in 2007) and Ayla (in 2009) that endangered the




46

lives and livelihoods of thousands of population.

4.1.5. Urbanization

Bangladesh has been experiencing a rapid expansion of urban areas since 1974. The proportion of

urban population increased gradually from 7% in 1974 to 28% (adjusted, including Statistical

Metropolitan Area) in 2011. SIZ upazilas showed a meager progress in urban growth. Most of the

upazilas hardly crossed double digit of urbanization rate in 2011. Cyclone Sidr and Ayla affected

upazilas recorded negative urban growth in 2011 compared to 2001. These upazilas were

Shyamnagar (5.42%), Koyra (5.89%) and Dacope (9.31%).

Figure 4: Population and urbanization rate of selected SIZ upazilas

4.1.6. Age Sex Distribution

Age-sex composition has environmental implications because different population subgroups

behave differently. According to 2011 census, the total male population in the SIZ upazilas was

1.07 million and female 1.09 million. The sex ratio of female overtops compared to male which

was 99.9 for SIZ upazila in 2011. The greater number of female population may be a reflection of

male out migration. Within SIZ upazila, female population was larger (sex ration below 100) in

Morrelganj (95), Shyamnagar (93), Koyra (97), Mathbaria (96) and Patharghata (97) upazila in

2011.

The age structure of SIZ upazila is quite interesting. The proportion of 65 years and above

population was almost doubled in SIZ area compared to national age structure. However,

economically active population was always below the national proportions. This indicates that the

dependency ratio (0-14 years and 65+ years) is higher in SIZ area. The proportion of the population

aged 15-49 accounts for 50.1% of the total population. This group of people is engaged in

harvesting resources from the SRF. Hence, the changes in age structure are closely associated with




47

resource extractions.

Figure 5: Broad age group wise population in SIZ districts and Bangladesh

4.1.7. Income and Poverty Situation

SIZ is relatively income poor and people are suffering from marginalization and inequality in

income. Among the SIZ upazilas, Head Count Ratio (HCR) for SIZ Satkhira (0.65) was higher

compared with 0.45 for non-SIZ upazilas of Satkhira, followed by SIZ Bagerhat (0.43) and non-

SIZ Bagerhat (0.24) and SIZ Khulna (0.41) and non-SIZ Khulna (0.32). These three districts are

lies in SRF area. The exceptions were found for Pirojpur and Barguna. Among the SIZ upazilas,

the guesstimated HCRs were higher for Shyamnagar (0.65), Dacope (0.60) Morrelganj (0.50),

Sarankhola (0.49), Mongla (0.42), Koyra (0.35) and Paikgachha (0.34).

Moreover, the proportion of people living below the extreme poverty and upper poverty line was

higher in SIZ upazila. Although, the percentage of people living below the extreme poverty line

decreased significantly, the percentage of people living below the upper poverty line increased

radically from 2005 to 2010 in Koyra, Paikgachha and Mathbaria. Among the SIZ districts and

upazilas, Sarankhola had the highest percentage of extreme poor people (28.2%) which was also

characterized by 48% of people living below the upper poverty line. Shyamnagar was the highest

poverty stricken area in 2010 (50.2% people were living below upper poverty line).




48

Table 2: Percentage of poor and extreme poor people in SIZ

District/

country

Upazila

2005 2010

% Extreme

poor (lower

poverty line)

% Poor

(Upper

poverty line)

% Extreme

poor (lower

poverty line)

% Poor

(Upper

poverty line)

Bagerhat Sadar 42.7 31.6 18.6 35.9

Sarankhola 62.8 48.7 28.2 48.0

Mongla 56.4 41.5 22.7 41.9

Morrelganj 64.0 50.3 27.0 46.5

Satkhira Shyamnagar 75.7 65.2 33.8 50.2

Khulna Koyra 50.0 34.8 29.1 49.1

Dacope 73.3 60.4 24.9 44.5

Paikgachha 49.6 34.4 23.3 42.4

Pirojpur Mathbaria 38.1 17.9 25.6 38.0

Barguna Patharghata 56.3 36.1 6.10 12.9

Bangladesh 25.1 40.0 17.6 31.5

Source: Poverty maps of Bangladesh, 2005 and 2010

4.2. Depletion of Sundarbans Forest Cover

Sundarbans have been losing its coverage, density, composition, and overall productivity. Forest

cover has decreased between 1983 and 1995 at an average annual rate of 0.12%, and average stand

density of the forest has been reduced by 87% between 1933 and 1995 (Sen, 2010).

A study conducted by Ministry of Environment and Forest on „Assessment of Sundarbans

Reserved Forest in 1960, 1985, 1995 and 2013‟. This research described the occupancy of different

mangrove species in different years. The study found that the areas covered by different forest

types had been decreasing at an alarming rate. The area occupied with Sundari tree was decreased

by 24% in 2013 (742.64 km2) compared with 1960 (985.51 km

2). The rate destruction was higher

in 1970s to 1990s. Most of the degradation (around 16% loss) held between 1960 (985.51 km2) and

1985 (828.45 km2). Although, around 1% of Sundari forest cover was lost during 1995 to 2013,

population size of SIZ increased by 8.31% during 1991 to 2011. During 1985 to 2013, around 14%

Sundari - Gewa forest cover was lost (1232.47 km2 in 1985 to 1022.74 km

2 in 2013). The

occupancy of Sundari - Passur tree decreased 93% between 1960 and 1985 (297.52 km2 in 1960 to

22.14 km2).

5. Discussions and Conclusions

The natural forest of Bangladesh has been depleted at an alarming rate. The annual loss of forest in

Bangladesh is estimated around 0.015 Mha (Choudhury and Hossain, 2011). The Sundarbans

mangrove ecosystems have remarkable value for south-west coastal communities and for the

country as a whole. But the forest resources are being destroyed at alarming rates. In general, the




49

more people in the frontier forest, the greater is the impact on forest and environment even when a

population and its growth are relatively small.

In reality, the size of population of SIZ locality in 2011 was declined from 2001. During this

period, the size of households, density of population and urbanization decreased significantly. The

annual population growth rate of SIZ districts also decreased dramatically. The urbanization rate in

SIZ upazila‟s was much lower than the other areas of the country. Population and poverty

processes were also intimately linked to forest cover change. Poverty is also a dominant

phenomenon in SIZ locality. The percentage of extreme poor (lower poverty line) people in SIZ is

higher than the national average. These extreme poor people are generally engaged themselves in

extracting natural resources either from Sundarbans or from common property.

During 2001 and 2011, the population growth rate of SIZ upazila was negative, yet the vegetated

land decreased. This could be explained by the climate change. The coastal zone was affected by

two major consecutive cyclones (Cyclone Sidr in 2007 and Cyclone Aila in 2009). These cyclones

endangered the lives and livelihoods of coastal communities. After cyclone Aila, more than 20,000

families have been displaced on the embankments and others near roads and collective centers from

Koyra and Dacope (IOM Displacement Tracking Matrix, February 2010). Many people seasonally

migrated from the SIZ for their livelihoods.

The population dynamics of SIZ locality provide a unique setting for examining population-

environment linkages. The population-environment linkages must be considered in the context of

the people and available natural resources. There is no doubt population growth is one of the

factors for depletion of forest resources from the SRF and theoretically, it is proved high population

density contributes to intense use of forests, fisheries, and water resources. But population factor is

not alone responsible factor for decreasing tree cover from the SRF. This study found that

population size was increased by 8.31% between 1991 and 2011, whereas almost at the same time

(from 1995 to 2013) Sundari tree cover decreased by 1%. Therefore, frontier population factor is

not alone responsible for depletion of tree cover from the SRF, there are some other factors like

upstream withdraw of water, illegal logging, expansion of shrimp and crab farming, frontier

agriculture, pollution, climate change included natural disasters e.g. tropical cyclones, coastal

erosion, storms surges, floods, hydrological changes, sea level rise, and above all lack of awareness

are interplaying in depletion of tree cover from the SRF. All of those mentioned factors need to be

synergistically considered while formulating any conservation efforts for Sundarbans. Otherwise

we will mistakenly put our blame to the frontier population only.

Acknowledgement: The author wishes to thanks to anonymous researchers, Bangladesh Bureau of

Statistics (BBS) and research institutions who published their scholarly articles on population data

and Sundarbans Impact Zones (SIZ). The author also declares no conflict of interest.

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