eurasian journal of science & engineering issn 2414-5629
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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:
Eurasian Journal of Science & Engineering
Ishik University, Erbil, Iraq
www.eajse.org
Eurasian Journal of Science & Engineering
ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE
Volume 2, Issue 1; December, 2016
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.
Eurasian Journal of Science & Engineering
ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE
Volume 2, Issue 1; December, 2016
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
Eurasian Journal of Science & Engineering
ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE
Volume 2, Issue 1; December, 2016
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:
Eurasian Journal of Science & Engineering
ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE
Volume 2, Issue 1; December, 2016
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( ) (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
Eurasian Journal of Science & Engineering
ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE
Volume 2, Issue 1; December, 2016
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).
Eurasian Journal of Science & Engineering
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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.
Eurasian Journal of Science & Engineering
ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE
Volume 2, Issue 1; December, 2016
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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%)
Eurasian Journal of Science & Engineering
ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE
Volume 2, Issue 1; December, 2016
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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
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(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 6: The variation of bottom pressure coefficient (Kb) along the bottom
gate surface for each gate openings
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.
Figure 7: The variation of bottom pressure coefficient (Kb) along the bottom
gate surface for each gate openings
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%)
Eurasian Journal of Science & Engineering
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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%).
Figure 8: The variation of bottom pressure coefficient (Kb) along the bottom
gate surface for each gate openings
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)
Eurasian Journal of Science & Engineering
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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.
Eurasian Journal of Science & Engineering
ISSN 2414-5629 (Print), ISSN 2414-5602 (Online) EAJSE
Volume 2, Issue 1; December, 2016
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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.
Email: [email protected]
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
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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
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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:
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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
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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,
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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
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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
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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)
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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)
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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)
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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.
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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.
Email: [email protected]
Received: September 9, 2016 Accepted: November 18, 2016 Online Published: December 1, 2016
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
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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
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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.
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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
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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
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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
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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.
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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).
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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
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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.
Email: [email protected]
Received: September 15, 2016 Accepted: November 4, 2016 Online Published: December 1, 2016
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
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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.
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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.
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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
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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
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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
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Table 4: Reinforcement percentage variation before and after extension and strengthening
requirement for typical interior columns, for concrete strength f’c = 56 MPa
Typical Interior columns F’c=56 MPa
floor(s) Col. No. Dim(mm) Existing
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 - -
Figure 4: Variation of steel ratio after extension for interior columns, for f’c =56MPa
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Table 5: Reinforcement percentage variation before and after extension and strengthening
requirement for typical interior columns, for concrete strength f’c = 84 MPa
Typical Interior columns F’c=84 MPa
floor(s) Col. No. Dim(mm) Existing
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 - -
Figure 5: Variation of steel ratio after extension for interior columns, for f’c =84MPa
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Table 6: Reinforcement percentage variation before and after extension and strengthening
requirement for typical edge columns, for concrete strength f’c = 28 MPa
Typical Edge columns F’c=28MPa
floor(s) Col. No. Dim(mm) Existing
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
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Table 7: Reinforcement percentage variation before and after extension and strengthening
requirement for typical edge columns, for concrete strength f’c = 56 MPa
Typical Edge columns F’c = 56 MPa
floor(s) Col. No. Dim(mm) Existing
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 - -
Figure 7: Variation of steel ratio after extension for edge columns, for f’c =56MPa
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Figure 8: Variation of steel ratio after extension for edge columns, for f’c =84MPa
Table 8: Reinforcement percentage variation before and after extension and strengthening
requirement for typical edge columns, for concrete strength f’c = 84 MPa
Typical Edge columns F’c = 84 MPa
floor(s) Col. No. Dim(mm) Existing
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 - -
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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%).
3. When NWC is used for the extension of existing building with column f’c = 56 MPa, the
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%).
4. When NWC is used for the extension of existing building with column f’c = 84 MPa, the
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).
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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.
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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.
Email: [email protected]
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.
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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
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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
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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
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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
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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
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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).
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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
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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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