Table of Contents (Department of Civil Engineering)
Table of Details
|
Thesis
Title |
NUMERICAL MODELLING OF EDGE SUPPORTED SLAB
RESPONSE |
|
Name
of the Student |
Sharmin Reza Chowdhury |
|
Supervisor Department |
Dr. Bashir Ahmed Assistant Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. March,
2000 |
|
Abstract |
Any satisfactory design requires the magnitude
of deflection of structural components of roof system at the service load to
be within acceptable limit. Excessive deflections of reinforced concrete roof
structures can cause severe serviceability problems. Although deflection is
an important parameter in the design of structure, enough emphasis is not
usually given to the calculation of slab deflection. None of the several
methods presently available for the calculation of deflection of slabs
provides the designer any unified approach to readily estimate the slab
deflection for any span ratio and support condition. This study briefly
reviews the methods available in literature for calculation of slab
deflection and attempts to develop a method to readily calculate the
deflection and moments of different types of slabs with various edge
conditions. With the aforesaid objective in mind, a
software analysis technique (Using a general purpose Fintie Element software
, ANSYS) has been used to study the behaviour of different types of edge
supported slabs. The results obtained from the Finite Element (FE) models
have been compared with those of the ACI moment coefficient method in order
to check the reliability of the method. The FE model has been used in the
parametric studies of deflection of slab with various edge conditions and
span-ratios. The results of parametric studies have been presented in tabular
form that forms the basis of an unified method for calculating the slab
deflection. Moreover, the present study provides a method
to compute the moment and deflection of slabs with opening. Results obtained
from the FE model have been used to develop chart that relate the strip
moments and deflection of such slabs with solid slabs. Using these charts it
becomes possible to calculate the moments and the deflection of such slabs by
simply multiplying the moments and deflections of the appropriate solid slab
with a correction factor. Finally, octagonal slabs with a few selected
supporting states have been analysed. An attempt is made to identify the
geometric dimensions of the slab when it can be treated as a rectangular slab
for design purpose. Results are presented in tabular form so that deflection
and moments of any octagonal slab with the selected support conditions can be
computed. |
|
Thesis
Title |
OPERATIONAL EFFICIENCY OF CONVENTIONAL IRON
REMOVAL PLANT IN MUNICIPAL WATER WORKS OF BANGLADESH |
|
Name
of the Student |
Shamsul Gafur Mahmud |
|
Supervisor Department |
Dr. Farooque Ahmed Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. 1999 |
|
Abstract |
In Bangladesh about ninety percent of
municipal water works are using ground water as a source of drinking water.
The reason is this water requires no treatment for bacterial contamination
and can be supplied directly. But ground water contains minerals like iron,
manganese and arsenic etc. of which iron is most commonly present in ground
water of this country. The presence of iron in ground is
generatingvarious complications in municipal water supply system. This
complication is not limited to technical aspect but also to the management of
municipal water works. The horizon of this complications due to this iron is
increasing as the number of thana towns are upgraded to municipalities. In the past, inadequate measures have been
taken to minimize the iron problem through installation of limited number of
iron removal plants. Due to resource constraints installation of IRPs in
large number could not be made possible. But with the increasing number of
municipalities the demand for removal of iron from water is growing. During
eightees, the Netherlands government came forward to minimize the problem and
installed a number of IRPs. But several operational difficulties showed up
within short period after commissioning. In course of time the plant
performances are reported to decline and their O & M cost stands so high
that it becomes very difficult for the municipal authority to meet these cost
out of their revenue income. In this study the declining performances of
the IRPs were investigated. The study also examined the effectiveness of
various steps of the treatment process and their findings were analyzed along
with observational, experimental and theoretical findings. During the study
it was found that these IRPs were not designed on the basis of any pilot
plant performance or on the basis of any laboratory model test. The study also reveals that plant performances
are declining due to some design faults. Design of Wash trough, filter
underdrain and determination of backwash rate in accordance to grain size are
worthwhile to mention. Poor backwash creates a couple of problems:
the impurities are not completely removed at one hand and on the other hand
premature filter breakthrough occurs which means water quality deteriorates
much before filter head loss reached to terminal head. It is found that no
plants could meet neither the designed water quality nor WHO guideline value
for drinking water. In this study, a laboratory model test was
performed in order to determine the unit processes of treatment that would
require for the study area on the basis of the investigation. A unit process
of treatment is selected and design outline is given on the basis of the
model test. Some operational procedures are suggested, as
observed during the study. If these were implemented, plant performances
would improve by 30 to 50% with respect to wash water requirement. Moreover
some modifications are also suggested to improve the performances of the
existing plants which can be made without disturbing whole process. These
will reduce the operational cost of the plants. For IRPs to be constructed in future it is
recommended to carryout detailed water quality investigation and pilot plant/laboratory
model study before construction of treatment plant in large a scale. It is
also recommended to strengthen close monitoring of plant performance with
special focus on day to day O & M. |
|
Thesis
Title |
DRINKING WATER QUALITY AND SANITATION CONDITION
OF FLOOD SHELTERS IN DHAKA CITY |
|
Name
of the Student |
Md. Rafiqul Islam |
|
Supervisor Department |
Dr. Md. Mafizur Rahman Asst. Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. September,
1999 |
|
Abstract |
Dhaka water supply and sewerage authority
(DWASA) in responsible for supplying potable water, Dhaka City Corporation
(DCC) is also responsible to make the city clean and to ensure safe
environment for the city dwellers. For different managerial problems they could
not serve these communal facilities. That is why city dwellers have to bear
enormous sufferings regarding quantity and quality of potable water and solid
waste disposal system. During natural disaster these problems become more
acute. Safe and pure water become precious thing and the access regarding
solid waste disposal becomes blocked. Hence it necessitates the study
regarding the identification and to make a possible solution of the problem
during disaster. Entire Dhaka City runs and is expanding in the
north-south direction. The western part of it is protected as the Dhaka
embankment runs along the western periphery. During 1998 flood western part
was affected much less than the eastern part. The study was conducted at the
time when the entire eastern part was submerged by a devastating flood in
1998. Water supply in the study area has resumed. About 66% of drinking water
supply lines in the flood shelters were under water. Sufferings regarding the
potable water and solid waste were acute. An extensive survey for the water
quality and solid waste management is done in the eastern part. For this purpose extensive field
investigations and a questionnaire survey among the affected people have been
made. A laboratory test program was undertaken to observe the water quality
of flood shelters. The important parameters those have been taken under
consideration are pH, color, turbidity, total coliform and fecal coliform. It was found that overall water quality of the
flood shelters exceeds the acceptable limit. Positive consciousness was not
observed among 93% of them regarding purification of the water. About 7%
people got access to the solid waste disposal system. |
|
Thesis
Title |
RAINWATER HARVESTING POTENTIAL IN BANGLADESH |
|
Name
of the Student |
Fateh-Ul-Anam Muhammad Shafee Yusuf |
|
Supervisor Department |
Dr. Md. Mafizur Rahman Assistant Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. August,
1999 |
|
Abstract |
In Bangladesh, surface water was the principal
source for drinking water ever upto recent past. However, during the recent
decades, due to the intensive development programs, the ground water is
utilized for drinking purpose in most rural areas. Unfortunately, recent
investigations have demonstrated almost countrywide occurrence of high
arsenic levels in the tubewell water. Today, Bangladesh seems to be one of
the most arsenic affected countries in the world. Bangladesh is a tropical
country and receives heavy rainfall during the rainy season. In the present context,
rainwater harvesting is being seriously considered as an alternative option
for water supply in Bangladesh. The objective of this research is to study the
potential of the rainwater harvesting system in Bangladesh. Ninety seven
percent of rural population has access to tubewell water and ground water is
still good for all type of uses except drinking. Therefore, the main emphasis
is given on the rainwater harvesting as a source of drinking water. The
research includes a literature review on rainwater harvesting systems, costs
and water quality. In performing the study, frequency analysis is
undertaken on annual rainfall data from 25 stations of Bangladesh
Meteorological Department (BMD). The most appropriate probability
distribution for each location is determined and used to estimate the
reliability of the system of that location. Based on this, design curves are
developed to estimate the reliability of the system for any consumption rate
at different areas in Bangladesh. Mass curve analysis is used to determine
required storage volumes for every location. Based on statistical analysis of
required storage volumes, design curves are developed for estimation of
storage tank volumes covering the need for dringing water of different
household sizes. These curves can be applied at field level by non
professionals. |
|
Thesis
Title |
SOIL-STRUCTURE INTERACTION EFFECTS ON TALL
BUILDINGS WITH MAT FOUNDATION |
|
Name
of the Student |
Md. Asif Iqbal |
|
Supervisor Department |
Dr. T. M. Al-Hussaini Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. July,
1999 |
|
Abstract |
Finite element analysis is performed to study
soil-structure interaction (SSI) effects on static and seismic response of
tall buildings on mat foundations. Simplified numerical models consisting of
beam-column elements and lumped masses are used to model building
superstructure including mat. For the static analysis, the soil is
represented by equivalent springs lumped at the foundation nodes. Results from
the static analysis show that the mat can be modeled realistically with
beam-column elements to represent the thick slab. It is also found that the
superstructure rigidity has some effects on the overall settlements and
bending moments in the mat. For seismic analysis, the soil is modeled by
frequency independent springs with viscous damping. Two and three-dimensional
models for different building layouts are used. Building height is varied
from six to ten stories. The influence of soil flexibility on the response of
the mat and the superstructure is studied. Parametric studies are performed
to evaluate the effects of different parameters on the behaviour of the
building. It is observed that soil-structure interaction, in general, results
in reduced base shear under seismic loading. SSI effects not only depend on
building configuration, but also are very much influenced by ground motion
characteristics. SSI effects are also found to be beneficial for building
with mass eccentricity where torsional response is important. |
|
Thesis
Title |
EFFECT OF INTERFACE ELEMENT TYPE ON
SOIL-STRUCTURE INTERACTION |
|
Name
of the Student |
Nur Sadeque |
|
Supervisor Department |
Dr. Md. Saiful Alam Siddiquee Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. Feb.
1999 |
|
Abstract |
A comprehensive literature survey and review
of all interface elements so far developed and implemented within their
limited scope of applications have been carried out in this study. From the
literature survey, three major types of interface elements such as, Goodman
(1968) Type, Katona (1983) Type and Desai (1984) Type have been selected for
further study depending on their successful application to physical problems.
These three most important interface elements are judged in an existing
nonlinear incremental-itrative generalized elsto-plastic Finite Element
Method (FEM) program. The parameters controlling the main features
of each interface elements have been identified. These parameters are
examined critically in a typical problem setting of direct-shear box
simulation. In order to investigate the evolution of different internal
variables like deformation, strain or stresses, various types of figures have
been drawn. Each case of analysis resulted in outputs of: (a) deformed mesh;
(b) force-deformation and stress-strain relationship inside the interface;
(c) shear strain contours; and (d) displacement fields. As most of the
figures were drawn at different load steps in order to trace the progress of
the variables, it was rather easy to identify the trouble spots for a
particular type of interface. The contrast between an analysis in
direct-shear box without an interface element and with an interface element
is very clear. Goodman (1968) type of interface performed well in direct
shear simulation. The performance of this interface depends on the relative
stiffness of the interface compared to the surrounding soil. Its behavior
also depends on the thickness of the interface and load eccentricity from the
interface. It shows distinct sign of mesh penetration at higher shear
deformation. Katona (1983) type interface element is the simplest interface
in terms of number of parameters required. It does not have any penetration
or separation problem. The performance in slip mode is ideal although not
realistic. The performance of Desai (1984) type interface element seems to be
the most realistic although it showed tendency of mesh penetration. It also
showed better convergence properties. Reduction in the thickness of the
element improves the performance of the Desai type element. Finally, it can be concluded that among the
three interfaces studied in this research, Katona and Desai type of interface
element are much better in accuracy and although, practically Goodman type of
interface is easy to formulate and to implement. |
|
Thesis
Title |
REMOVAL OF ARSENIC FROM WATER BY FERRIC
CHLORIDE |
|
Name
of the Student |
Nibedita Chowdhury |
|
Supervisor Department |
Dr. M. Ashraf Ali Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. October,
1999 |
|
Abstract |
Widespread arsenic contamination of
groundwater has become a major public health concern in Bangladesh, where
water supply is heavily dependent on groundwater. The present study focused
on removal of arsenic from groundwater by coagulation with ferric chloride.
Removal of both As (V) and As (III) was found to increase with increasing
coagulant (ferric chloride) dose. For higher coagulant (ferric chloride)
doses, removal efficiencies appear to be independent of initial arsenic
concentration. Removal efficiency of As (III) by ferric chloride was found to
be significantly lower than that of As (V). For example, 25mg/L of ferric
chloride could bring down As (V) concentration to less than 10mg/L from an
initial concentration of 0.25 mg/L; whereas in case of As (III) a ferric
chloride dose as high as 125 mg/L resulted in a residual arsenic
concentration of about 55mg/L,
higher than the drinking water standard (50mg/L) set by the Bangladesh EQS. It was found
that removal efficiency of As (III) pre-oxidized with bleaching powder was
almost identical to that of As (V). For a sorbate/sorbent ratio (expresse as
mg As/mg Fe)
of about 50 or less, removal efficiencies exceeding 95 percent could be
achieved, irrespective of the initial arsenic concentration. This can serve
as a guideline value or thumb rule in determining required dose of ferric
chloride for arsenic removal. A maximum adsorption density of about 353mg As/mg Fe
was achieved with a As(III) (pre-oxidized) concentration of 2.0 mg/L and
ferric chloride concentration of 25 mg/L. However, at optimum sorbate/sorbent
ratios (i.e., 50 or less) maximum adsorption density achieved was much less,
about 50mg
As/L mgFe. Since significant fraction of arsenic in the
groundwater of Bangladesh can exist as As(III), it appears that arsenic
removal technology based on ferric chloride coagulation must involve a
pre-oxidation step for converting As(III) to As (V). In this study, good
removal of As(III) was achieved in jar tests using a chlorine (bleaching
powder) dose 3 to 4 times that calculated from stoichiometric consideration.
However, the unstable nature of bleaching powder is a cause of concern in its
use as an oxidant. Results obtained from this study enabled determination of
ferric chloride dose required for achieving a particular removal goal for
arsenic present at different initial concentrations. It was found that ferric
chloride requirement for satisfying the WHO standard (10mg/L) was significantly
higher than the required for satisfying the Bangladesh standard of 50mg/L. Thus,
the cost of arsenic removal by ferric chloride would depend on the water
quality standard it is designed for. This is important in view of the
possible revision of the drinking water standard for arsenic in many
countries. In Bangladesh, arsenic removal by coagulated flocs of ferric
hydroxide could be a very effective technique, particularly in view of the
presence of elevated levels of iron in many regions of the country. Removal of As(V) appears to be maximum in the
neutral pH range and slightly depressed at higher pH values, exceeding 8.
Since pH of groundwater usually falls between 6 and 8 in Bangladesh, pH is
not likely to play a major role in determining the removal of arsenic from
groundwater by ferric chloride. Although pH has a more pronounced effect on
As(III) removal, this may not be an important consideration for arsenic
removal by ferric chloride involving pre-oxidation. Phosphate appears to have
a dramatic effect on arsenic removal from groundwater. Removal of arsenic
present at an initial concentration of 0.10 mg/L (and treated with 10 mg/L of
ferric chloride) came down from 92 percent (in the absence of phosphate) to
about 46 percent in the presence of 2mg/L of phosphate. Relatively high
concentrations of phosphate, reaching as high as 5.8 mg/L, have been found in
some places of Bangladesh and it appears that ferric chloride doses
determined from laboratory batch studies (without the presence of phosphate)
can significantly understimate the actual dose requirement. Effect of
phosphate on arsenic removal by ferric chloride also suggest that phosphate
ions can play an important role in the release of arsenic in the groundwater
environment in Bangladesh. |
|
Thesis
Title |
|
|
Name
of the Student |
Roksana Mannan |
|
Supervisor Department |
Dr. Mehedi Ahmed Ansary Asstt. Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. December,
1999 |
|
Abstract |
This research presents the development of an
Interactive Database for different soil parameters for different areas of
Dhaka City based on Artificial Neural Networks (ANN). Since it is expensive
to obtain extensive information regarding soil parameters of a region, ANN
can be used to generalize soil data over three-dimensional space. Soil data
from the existing soil reports are used to
train a hierarchy of artificial neural networks for this purpose. The
study has been divided into two phases. In the first phase of the study, soil
reports have been collected from different Government and Non-government
organization to prepare a relational database based on Microsoft Access
Software which is readily available in most of the Personal Computers. This
database can be used effectively for the preliminary design of any
geotechnical structures. Artificial neural network has the capacity to map a
very complex relationship among different parameters of a complex phenomena.
It can generalize and interpolate the missing data in any possible direction.
Thereby a complete three dimensional geotechmical database of an area can be
obtained. In the second phase of the study, back-propagation neural networks
has been used to simulate soil strength parameters (SPT and Unconfined
Compression Strength) in three dimension using the data from the geotechimcal
database developed in the first phase of the study. The variable used in the
models are Topographical Information, Depth, Specific Gravity (GS), Water
Content, Dry Density, Percentage of Sand, Silt and Clay, Liquid Limit and
Plastic Limit. The Database contains 140 borehole data of
Dhaka. The database can be updated easily and data of any place of Bangladesh
can be added. The training of the ANN system is performed based on the
available data of SPT, UCS and other available soil parameters stored in the
database. The modeling approach has been found to be successful. The model
predictions are convergent with the observed results. It has been observed
that water content and dry density have significant effect on both SPT and
UCS. The other soil parameters GS, %Sand, % Silt, %Clay. LL or PL do not have
individual effect on SPT and UCS, but together with other variables they can
be used to predict SPT and UCS up to a depth of 25ft. additionally, %Sand,
%Silt and %Clay together with Topographical Information and Depth has been
used for prediction of SPT up to a depth of 100ft. The methodology and application developed in
this research can be extended, in many directions. A framework that
integrates spatially enhanced GIS systems with 3D graphics representation
using a shared database can be developed. Also similar ANN models for
predicting soil strength paramenters for other areas of Bangladesh can be
developed. |
|
Thesis
Title |
SLOPE STABILITY AND SETTLEMENT ANALYSIS OF
DHAKA FLOOD PROTECTION EMANKMENT |
|
Name
of the Student |
Md. Shamsul Islam |
|
Supervisor Department |
Dr. Mehedi Ahmed Ansary Assistant Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg January,
2000 |
|
Abstract |
The severe flooding in 1987 led to the design
and construction of about 30 km long flood control embankment on the Western
side of Dhaka city. In some of the stretches, the embankment crossed silted
up channel consisting of soft subsoils. Approximately 13 km of the embankment
suffered some sort of failure immediately after construction, including slip
failures and failure due to plastic lateral spread of the subsoils.
Subsequent studies by local and foreign Consultants identified several
failure zones. Based on those studies three locations of the embankment at
Mirpur and two locations at Kellar Mohr site have been selected for this study.
Detailed field and laboratory investigations were carried out. Based on the
results of soil investigations, stability analysis using XSTABL at five
critical sections (9500, 9900, 13925, 29930, 30000) of the embankment were
performed compared with previous analysis. It has been found that stability
of the embankment increased significantly within the last few years. This can
be attributed to the fact that repeated dumping of soil at the top of the
embankment and consequent settlement of the embankment has improved the
properties of soil. The settlement analysis has been performed for three
critical sections 9900, 13925, 29930 of the embankment. The analysis is based
on the soil parameters obtained during the construction phase of the
embankment. Finite Element program CRISP has been used for modeling
settlement of the embankment. Consolidation analysis with elastic-anisotropic
model ahs been used. The loading is due to the self-weight of the body of the
embankment. Loading has been transferred on the foundation of the embankment
in three stages using remove-add mechanism of CRISP, to simulate embankment
construction sequence. Maximum settlement estimated for the embankment top at
9900, 13925 and 29930 are 4.07ft, 5.44ft and 3.49 ft respectively. |
|
Thesis
Title |
SEISMIC MICROZONATION OF DHAKA CITY BASED ON
SITE AMPLIFICATION AND LIQUEFACTION |
|
Name
of the Student |
Md. Abdur Rashid |
|
Supervisor Department |
Dr. Mehedi Ahmed Ansary Assistant Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. February,
2000 |
|
Abstract |
Microzonation is a systematic way for the
management of earthquake vulnerability, integrating for application the earth
and engineering sciences. It can be achieved by inputting local site
characteristics, ground shaking, liquefaction, slope stability, high ground
water, fault rapture, economic involvement such as land cost, transportation
costs, seismic damage etc. In the present study local site conditions and
liquefaction potential of sites were used for mixrozonation of Dhaka city.
Dhaka was first divided into small grids. At the grid points shear wave
velocities were estimated by using SPT test results. More than two hundred
bore hole data were collected and converted into shear wave velocities using
empirical relations. All these data were used to estimate vibration
characteristics at different grid points of the city employing one
dimensional wave propagation program SHAKE. The computation were made in the
frequency range of 0 to 20 Hz. At frequencies every 0.05 Hz interval. The
loss of energy of seismic waves in the soil layers was also considered. The
vibration characteristics of each site such as predominant frequency and
amplification amplitudes were found. The predominant frequency (inverse of
period) at the site is an important information in estimating the input force
to a structure due to the earthquake. The amplification amplitude is the
relative amplification of a seismic wave at ground surface level coming from
baserock. In this study, at each site of Dhaka city,
liquefaction potential was analysed using maximum acceleration of 150 cm/s2.
This maximum acceleration is based on 200 years Peak ground surface
acceleration contour estimated from earthquake hazard analysis for Bangladesh
based on National Oceanic and Atmospheric Administration (NOAA) earthquake
data from 1900 to 1977. The liquefaction potential of different locations of
Dhaka is estimated by two methods: The Seed et al. method (1983) where SPT
data was used and Iwasaki et al. method (1982) based on topographical
information. The results of the amplification and
liquefaction analysis were transformed into microzonation maps depicting :
(i) zones showing quantitative estimates of site amplification; (ii) zones
showing the natural frequency of the soils; (iii) zones showing qualitative
estimates of liquefaction potential; (iv) zones showing quantitative
estimates of liquefaction potential. These maps will be useful for
preliminary selection of a project site, land use planning zoning ordinances,
pre-disaster planning, capital investment planning etc. |
|
Thesis
Title |
EARTHQUAKE HAZARD ANALYSIS FOR BANGLADESH |
|
Name
of the Student |
Mohammad Sharfuddin |
|
Supervisor Department |
Dr. Mehedi Ahmed Ansary Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. Aprin,
2001 |
|
Abstract |
As a first step in earthquake disaster
mitigation, this study aims to identify and evaluate the seismic hazards in
Bangladesh. The seismic environment of Bangladesh is first studied. This
includes geological and seismotectonic setup in Bangladesh, probable major
seismic sources, existing zoning maps etc. Due to the lack of a proper seismotectionic
map in the region under consideration, the insufficiency of data and high
uncertainties in seismic source parameters, a simple model for earthquake
occurrence using a newly developed earthquake catalogue is used. Initially a
detailed earthquake catalogue analysis is carried out to understand the
nature of seismicity. For the development of the catalogue, earthquake data
are collected from various sources, such as ISC, ISS, USGS, RRLJ and other
independent researchers. Different correlations are developed using the
collected data to homogenize earthquake magnitudes. The data completeness of
the earthquake catalogue is examined and the time periods in which the data
are complete are identified for each magnitude. For the maximum use of the
available data, the data of the large earthquakes are taken from the long
time period while the data of small earthquakes are taken from the shorter
time period in which they are complete. Using the simple catalogue based model; the
seismic hazard at 42 points in Bangladesh is estimated. The seismic hazard
maps are presented as contour maps in terms of horizontal Peak Ground
Acceleration (PGA) based on 50, 100, 200 years return period and 10%
probability of exceedance in a design life of 50 years. A return period
seismic hazard map for PGA³150
cm/s2 is also presented. In addition expected Ms values for 34
points are estimated for 50,100 and 200 years return period. By comparing the seismic base shear
coefficients with the values of the hazard maps, a new seismic zoning map for
short period structures are proposed based on the 200 year PGA. Similar to
the BNBC 1993 seismic zoning map, the proposed map has three seismic zones.
It assigns higher seismicity to Bandarban, Faridpur, Kustia, Natore,
Nilphamari, Panchogarh, Rajshahi, Sandwip and significant part of Bogra,
Cox’sbazar, Khargrachari, Noakhali, Rangamati and Rangpur. These areas have
been assigned low seismicity in the seismic zoning map of BNBC 1993. The finding of this study shows that
considerable seismic hazard exists for major parts of the country. Based on
the 1991 Census data and proposed seismic zoning map, about 42 million
people, representing one third of the total population live in Zone 3 (38%
area), i.e. areas which may be classified as “liable to severe damage”,
another 52 million (i.e. approx. 46% of the population) live in Zone 2 (39% area),
i.e. areas “liable to moderate damage” and the rest 19 million population
live in Zone 1(23% area), i.e. areas “liable to slight damage”. The outcome
of this study, coupled with vulnerability studies, must guide, stimulate and
facilitate the efforts of the respective government, the earthquake
engineering and the disaster mitigation planning communities to take specific
practical preventive measures to reduce seismic risk of Bangladesh. |
|
Thesis
Title |
STUDY OF VEHICLE ARRIVAL PATTERN AND FREE
SPEED CHARACTERISTICS ON SELECTED NATIONAL HIGHWAYS |
|
Name
of the Student |
Gazi Arif Iqbal |
|
Supervisor Department |
Dr. Moazzem Hossain Assistant Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. August,
1998 |
|
Abstract |
Analysis and interpretation of traffic
operations on national highways require a sound understanding of the traffic
flow parameters. Such traffic flow parameters are traffic arrival headways,
free speed of vehicles, operating speed and speed-flow-density relationship.
No significant study has yet been made to investigate these traffic
parameters of Bangladeshi national highways. In this study, effort has been
given to investigate the traffic arrival pattern and free speed
characteristics of vehicles on two-lane two-way national highways of
Bangladesh. The research study has been based on field data. Both video and
manual data on the traffic flow of selected national highways have been
collected for a net period of approximately twenty five hours. The analysis
of collected data has been made using different statistical softwares.
Analysis of traffic arrival pattern using the vehicular time headway data has
revealed that the pattern follows more than one statistical distribution
models for all the highways. Generally, it has been observed that the
vehicles maintain close headways when they are in following situation. It has
been observed that the traffic arrival pattern on selected Bangladeshi
national highways can be described by one or more of the two statistical
distributions, namely, exponential and lognormal. The relevant parameters of
the corresponding arrival headway distributions have been estimated. Analysis
of free speed of the commonly found vehicles (bus, minibus, truck,
passenger-car, nonmotorised vehicles) follow normal distribution pattern.
Corresponding parameters of the normal distribution have also been estimated.
From regression analysis, it has been found that free speed of vehicles
depends on the pavement and shoulder width. In a pavement width range of 5.8m
to 7.5m, free speed of commonly found motorized vehicles increases with the
increase in shoulder width except for the case of bus (the reason of which
has been identified as a local phenomenon on a particular highway). |
|
Thesis
Title |
|
|
Name
of the Student |
Md. Arifur Rahman |
|
Supervisor Department |
Dr. Moazzem Hossain Assistant Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. August,
1998 |
|
Abstract |
In case of two-lane two-way highways, drivers’
overtaking manoeuvres has significant bearings on the design and control
measures. Parameter related to drivers’ overtaking is, therefore, useful to
the highway engineers in setting geometric design criteria and implementing
traffic control measures on the highways. This research study has been
undertaken with the objective of comprehensive understanding of the drivers’
overtaking process on the national highways, (which are basically two-lane
two-way type) of Bangladesh. An empirical approach based on extensive real
field data has been adopted for the present study. Both video and manual data
on the traffic operation of national highways have been collected for a
period of over two months. Then the relevant data items have been transformed
in use-able format. The collected data items have been analysed using
different statistical computer softwares. It has been observed that the whole
overtaking manoeuvre can be divided into four clearly identifiable distance
elements as suggested by earlier studies of AASHTO. These are trailing
distance (d1), overtaking distance (d2), clear distance
(d3) and lag time distance (d4). However, these
elements in the case of national highways of Bangladesh have been estimated
and analysed in this research study. The analysis reveals that all the four
components of overtaking process follow normal distribution model. But there
are variations in the values of these elements depending on the vehicle size
(larger/smaller) and type (motorized/non-motorised). Total overtaking sight
distance required for the drivers’ overtaking manoeuvre has been estimated
from the four distance elements. This total distance has also been compared
with the AASHTO design criteria. It has been found that the total sight
distance required for overtaking vehicle on the selected national highway is
smaller im comparison to that suggested by ASSHTO for the same speed group.
Regression analysis of overtaking distance and speed difference of vehicles
involved reveals that there is a linear relationship between the two.
Generally, overtaking time and distances decrease with the increase of speed
difference when other conditions remain same. It has also been observed that
there is a strong relationship between the overtaking of vehicles and actual
pavement width and shoulder condition of the highway. Generally, on wider
highways with stable shoulder the number of successful overtakings are higher
than the corresponding number in case of narrow pavement with unstable
shoulder. |
|
Thesis
Title |
CHARACTERISTICS OF MAJOR INDUSTRIAL LIQUID
POLLUTANTS IN BANGLADESH |
|
Name
of the Student |
Md. Ashiqur Rahman |
|
Supervisor Department |
Dr. Md. Delwar Hossain Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. October,
1997 |
|
Abstract |
Bangladesh is promoting rapid industrial
development and on the other hand industries contribute to serious pollution
problems, since a large number of industries discharge their wastes,
including potentially toxic substances, without treatment directly into the
environment. The characterization of this raw waste is an essential component
of the overall planning for effective and economical methods of industrial
liquid waste pollution control. The treatment units for different types of
industries can be designed with due consideration to the varying nature of
industrial waste characteristics. Therefore, characterization of industrial
liquid wastes prior to a treatment plant design is very important. On the
basis of pollution effect on the environment, the major industries in
Bangladesh are categorized as textile, tannery, pharmaceutical, fertilizer,
paper and pulp, vegetable oil, sugar, cement, steel, paint and chemical
industry. Most of the industries under these categories do not have any type
of treatment facilities and they routinely discharge their raw wastes; which
contains various toxic and hazardous substances directly or through the local
storm drainage system to nearby khal, lake or river. To quantify the
characteristics of major industrial liquid pollutants in Bangladesh, the
important parameters those have been taken under consideration are pH, BOD5,COD,
SS,TS, inorganic substances (Nitrogen, Phosphorous, Chlorides), sulphate,
sulphide, heavy metals (Cu,ZN, Hg, Cr, Pb), colour and turbidity. The study
was conducted through collecting different industrial effluent test results
from the Environmental Engineering Laboratory, BUET and then analysed by
using computer software (EXCEL). The study reveals that in most cases, the
concentration of these parameters exceed the respective EQS for discharge
into a surface water body. Since river water is largely used for drinking,
washing, irrigation and fisheries purposes; serious adverse economic,
environmental and human health effects occur due to the discharge of
industrial liquid pollutants in surface water bodies. A wide variation of the range of
characteristics of different parameters has been observed in the same
categorized industries. The characteristics of industrial liquid wastes in
our country vary from place to place and depend on various factors like raw
materials used, manufacturing process, condition of machinery, water supply
position, weather condition of the locality etc. With due Consideration of
these factors and from laboratory analyses of wastes a general
characteristics of major industrial liquid pollutants has been proposed in
this study. Results of this study suggest that the effluents from different
categorized industries need to be properly treated before discharge into a
surface water body. |
|
Thesis
Title |
REMOVAL OF MICROORGANISM AND SUSPENDED
MATERIAL BY COAGULATION AND FILTRATION |
|
Name
of the Student |
Sultana Naznin Afroze |
|
Supervisor Department |
Dr. Md. Delwar Hossain Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. Apruil,
1998 |
|
Abstract |
The quality of water is of vital concern for
mankind since it is directly linked with human welfare. But majority of
people are still not aware of it. People use surface water for various
domestic purposes. Surface water is often physically and bacteriologically
contaminated due to unhygienic practices. During floods the water quality deteriorates
and treatement is required to make water potable. The study was devoted to acquire a better
understanding of the effectiveness of alum for removal of faecal coliform as
well as kaolin particles. Different parameters affecting removal of faecal
coliform and kaolin particles were investigated in this study such as alum
dosage, pH, sedimentation time and mixing. Filtration with filter paper was
performed after coagulation. Removal of faecal coliform was observed at
different pH and sedimentation time. Alum dosage was found effective for reduction
of faecal coliform and kaolin particles. With increasing alum dosage faecal
coliform and turbidity removal rate were found increasing pH and
sedimentation time also significantly affected the removal of faecal coliform
and turbidity. Most of the experiments were performed at pH 4.5 and 6.0. It
was observed that the removal efficiency at pH 6.0 was higher than that of pH
4.5. At any alum dosage, removal of faecal coliform
was found to increase with increasing sedimentation time. Moreover for the
same removal of microorganism less sedimentation time was required for
increased alum dosage. With increasing sedimentation time settlement rate was
found to decrease. It was found that with increasing alum dosage potable water
could be obtained within a short period of sedimentation. |
|
Thesis
Title |
TREATMENT OF LIQUID WASTE FROM A TEXTILE
INDUSTRY WITH WATER HYACINTH |
|
Name
of the Student |
Sania Huq |
|
Supervisor Department |
Dr. Md. Delwar Hossain Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. September,
1998 |
|
Abstract |
Waste water treatment using aquatic plants is
gradually gaining importance. The aquatic treatment system consists of one or
more shallow ponds in which one or more species of aquatic macrophytes are
grown. Waterhyacinth is one of the most promising aquatic plant which has
been successfully used all over the world in industrial waste water
treatment. In this study an experimental investigation has been carried out
to find the effectiveness of water hyacinth in control of pollution by
textile liquid waste. This study focuses on the characteristics of
liquid waste of existing textile industries in Bangladesh. In our country
very small efforts are made for the treatment of industrial waste. Most of
the existing industries dispose off liquid waste having pollution indication
parameters exceeding the respective environmental quality standard. This
study shows that the effluents from these industries can be effectively treated
by water hyacinth ponds as an alternate low cost treatment method before
discharge of raw liquid waste into a surface waterbody. In this study different experiments have been
conducted to determine the removal rate of pollutants with giving importance
to colour, turbidity, suspended solids from textile liquid waste at different
concentrations of waste water and at different pH. Ignoring the effect of
different types of water hyacinth in the treatment of waste water, in this
study plants having long and extensive root system are used. Representative
samples of Beximco Textile Industry were collected and polluting parameters
were analysed in the Environmental Engineering laboratory of BUET. Water
hyacinth was used to treat this liquid waste at different concentrations in
some plastic buckets. Samples from these buckets were collected at regular
interval and pollutant contents were determined. This process was repeated to
determine the removal of pollutants by water hyacinth at different pH of raw
effluent. This study reveals that water hyacinth could
be positively used in the treatment of waste water. It has found that removal
rate of pollutants by water hyacinth are excellent if the waste water is
diluted fifty percent. Test results also show that removal rate of pollutants
at pH 4.8 are much better than at pH 6.8 of the waste water. Treatment of textile liquid waste by
coagulation and sedimentation process gives a better understanding of the
effectiveness of alum for removal of pollutant. An attempt was made to remove
pollutants from textile liquid waste by sludge blanket and coal filter
method. |
|
Thesis
Title |
REMOVAL OF IRON FROM GROUND WATER BY
COAGULATION AND SEDIMENTATION |
|
Name
of the Student |
Salma shahid |
|
Supervisor Department |
Dr. Md. Delwar Hossain Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. December,
1998 |
|
Abstract |
Ground water is a major source of safe water
for drinking and other domestic purposes for the rural/urban population of
Bangladesh which may have iron content in excess of 5 mg/L. This study is an
experimental investigation to observe the effect of different factors in iron
removal and also to develop simple and cost effective iron removal method. Relevant literature on chemistry of iron
content water and unit processes of iron removal have been reviewed, and
water use pattern and distribution of iron in ground water have also been
focused. Investigations were made at laboratory
condition on artificial iron content water and natural ground water collected
from tubewells of iron prone areas to find out effect of different unit
processes and other related factors on iron removal Experimental results
shows that filtration is an effective mode of iron removal. However,
considering the frequent cleaning of the filter bed and low yield, in this
study emphasis have been given on sedimentation, for effective and efficient
iron removal. As an aid in improving settling characteristics of the
precipitated iron, coagulation is observed to be an important tool. Aeration, coagulation and 30 min sedimentation
can reduce iron concentration to allowable limit of 1 mg/L. However, the
analysis also shows that iron removal increases with an increase in anion
concentration. More pronounced effect is observed when the added anion is
common to the anion already in solution, due to common ion effect. Alum used
as coagulant is observed to be more effective than lime in iron removal.
Whereas, the coagulant cost involved using alum as coagulant is 191.7% higher
than lime. |
|
Thesis
Title |
ENVIRONMENTAL IMPACT ASSESSMENT OF INTRODUCING
LIGHT RAIL TRANSIT IN DHAKA CITY |
|
Name
of the Student |
S. M. Zulkernine |
|
Supervisor Department |
Dr. Md. Delwar Hossain Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. August,
1999 |
|
Abstract |
Dhaka, the capital of Bangladesh, is a large
city, which is going to be one of the mega cities of the world within the
early next century. Among other problems of a mega city, Dhaka is being faced
with the environmental degradation of the city. The population of Dhaka has
increased substantially since the independence of the country and eventually
the number of motorized transport has increased to meet the increasing demand
of the city dwellers. The harmful gases emitted from these vehicles are
polluting the air of the city and has put the health of the city dwellers in
danger. Besides this, accident rate has increased and traffic congestion has
become a regular phenomena. To cope with this problems an alternative
transportation system has become imperative which will be environment
friendly and have the potential to meet the demand of the city. Light Rail
Transit, which is a modern version of the traditional tramway, can be a
probable solution to this problem. This study was designed to find out the
environmental impact of the introduction of Light Rail Transit in Dhaka city.
In doing this relevant literature have been reviewed. A route for LRT has
been proposed and data collected through sample survey. However the
feasibility to establish a track for LRT was not carried out purposely as
that was out of the scope of the study. Through the study, it appears that because of
the introduction of Light Rail Transit, a substantial number of people will
be diverted to LRT from other modes of transport and as a result emission of
harmful gases like SOx, NOx and COx will be
reduced by about 40%. |
|
Thesis
Title |
CORRELATION OF ARSENIC AND IRON IN GROUNDWATER
OF BANGLADESH |
|
Name
of the Student |
Mst. Anjuman Ara |
|
Supervisor Department |
Dr. Md. Delwar Hossain Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. August,
2000 |
|
Abstract |
Water is a basic necessity of man along with
food and air. In Bangladesh groundwater is a major source of safe water for
drinking and other domestic purposes for the rural and ruban population.
Groundwater contains dissolved minerals such as iron, arsenic, manganese,
nitrate, fluoride, chloride, calcium, sodium etc. Presence of elevated levels
of arsenic in groundwater has become a major concern in Bangladesh and
elevated levels of iron are also present in many regions of the country. This
study is an attempt to evaluate the possible correlation between the presence
of Arsenic and Iron in groundwater. In order to assess possible correction between
arsinic and irom concentration in groundwater, 760 tubewell water samples
were analyzed. These tubewells covers the north-eastern zome of Bangladesh,
and the districts of Manikgonj and Noakhali. About 64% of the tubewells
contain iron above 1.0 mg/1 and exceed Bangladesh standard and about 34% of
the tubewells contain iron exceeding 5.0 mg/1. About 34% of the tubewells
contain arsenic above 0.05 mg/1 which is the Bangladesh standard for Arsenic.
These tubewells are a potential
threat to public health. The overall correlation between arsenic and
iron concentration of tubewell water in the study-area in Bangladesh is poor.
But in some districts a positive correlation has been observed and in some
than as the positive correlation is very strong. Arsenic concentration
analysis of groundwater form 3912 tubewell water samples were performed and
it was found that about 31% of the tubewells in Bangladesh have arsenic
concentration above 0.05 mg/1 which poses a potential threat to public
health. In general if Arsenic concentration is higher,
Iron concentration is also higher. |
|
Thesis
Title |
INFLUENCE OF SALINITY ON THE PERFORMANCE OF A
SLUDGE BLANKET CLARIFIER |
|
Name
of the Student |
Misbah Uddin Khan |
|
Supervisor Department |
Dr. Md. Delwar Hossain Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. April,
2000 |
|
Abstract |
Coagulation is an important technique in water
treatment to remove colloidal and non-settlable fine particle successfully.
These particles are forced to settle as floc with the help of chemicals and
particle transport mechanism. Common coagulant does is slum [Al2(SO4)3.
14 H2O], readily dissolves in water, is used in the pH range of
5.5 to 7.8. One of the limitations of coagulation is influence of salinity.
Additon of salts interferes in the coagulation and, alum floc breaks in
presence of salinity in water CWASA faced the salinity problem in 1991 for
cyclone tide and in 1995 for backwater effect of sea. To review CWASA’s
problem during saline intrusion and improve the situation, a physical model
of sludge blanket clarifier which angle is same to Mohara Treatment Plant’s
clarifier has been set-up for this study. Both the clarifiers work in the
same method, hence, clarifier used in the laboratory can be considered
similar to Mohara’s clarifier. It was found that saline intrusion problem
could be minimized by controlling flow. Performance Study for different units of the
plant for selected parameters, i.e., pH, turbidity, colour, Total Dissolved
Solid (TDS), Total Solid (TS), alkalinity and chloride have been done for
each unit of the plant and for the whole plant taking samples at inlet and
outlet of each unit. The study reveals that sedimentation unit of the plant is
good in removing turbidity and Total Suspended Solid (TSS). Coagulation
unit’s Flash mixer and Clarifier unit) performance in removing colour and
turbidity is about 75-95%. Mohara Treatment Plant is performing well in
removing turbidity, colour and TS. Alkalinity, pH and chloride of finished
water were always in the range comparing World Health Organisation (WHO)
guideline. This study has been done at low flow (winter season) condition of
river Halda. Further study of the plant is required at high flow condition
and during saline instrusion. The study shows that performance of clarifier
depends on discharge, angle of clarifier with horizontal and depth of sludge.
Critical discharge for the clarifier used in the study when sludge blanket
disintegrates initially due to concentrated force was about 936 cm3/s/m3
of sludge. Clarifier’s performance decreases when salt is added at any flow.
Increased salt increases density of water, hence concentrated force increases
at the inlet of clarifier. Increased concentrated force increases initial
dispersion of floc in the clarifier. But 134-535 cm3/s/m3
of sludge is the optimum discharge range for the clarifier used when
performance is good at optimum salt value. Limiting chloride was found 1000
mg/1 from limiting concentrated force of 24764 c.g.s. unit. Unit at 17.5 cm
sludge depth for the clarifier used in the laboratory. Maximum tolerable
discharge for the clarifier used during salinity was about 893 cm3/s/m3
of sludge at minimum 500 mg/1 of chloride, while maximum tolerable chloride
was about 3400 mg/1 at minimum discharge of 80 cm3/s/m3
of sludge. Again, maximum tolerable discharge for clarifier of Mohara during
salinity was about 2219 cm3/s/m3 of sludge at minimum
500 mg/1 of chloride, while maximum tolerable chloride was about 6800 mg/1 at
minimum discharge of 80 cm3/s/m3 of sludge. Upto 3400
mg/1 of chloride and at minimum discharge of 80 cm3/s/m3
of sludge, clarifier’s performance can be considered similar to slow mixing
coagulation. CWASA could control both discharge and chloride at the flash
mixer during salinity intrusion. |
|
Thesis
Title |
A RATIONAL DESIGN OF SIMPLY SUPPORTED AND
CONTINUOUS DEEP BEAMS |
|
Name
of the Student |
Syed Md. Mymur Sultan |
|
Supervisor Department |
Dr. Salek M. Seraj Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. September,
2000 |
|
Abstract |
Deep beam is a very important structural
element in various types of concrete structures such as pile cap, transfer
girder, panel beams, foundation walls of rectangular tanks and bins, shear
walls, folded Plate roof structures, etc. Analysis of deep beams under shear
is quite complex’ and because of the complexities involved, exact theoretical
basis for the analysis of deep beams in shear has not yet developed. Current
design rules for deep beams are largely based on the provisions of American
Concrete Institute (ACI) Code, Construction Industry Research and Information
Association (CIRIA) Guide, and other codes and design methods. The
present-day design provisions for deep beams are usually based on test result
conducted on simply supported model deep beams, although deep beams are often
continuous. Again, some of the provisions for the design of deep beams are
essentially those for slender beams and are not applicable to deep beams. In the absence of an exact and simplified
basis for the design of deep beams, several new lines of thinking have
developed in the recent past in order to unify the design of various
structural concrete members. One of these new approaches is the concept of
Compressive Force Path (CFP). However, a very limited number of tests have
been conducted to verify the applicability of this method in the design of
deep beams. One of the primary purposes of this study is
to try to understand the behaviour of deep beams with the help of tests
conducted by various researchers. Again, available test results have been
used, in conjunction with results from the limited tests conducted by the
investigator on simply supported as well as continuous deep beams, in finding
out the suitability of CFP method in the design of deep beams. In the present study, test data of about 175
deep beams have been collected, analysed and employed in understanding the
behaviour and predicting the strength of such members using ACI, CFP and
CIRIA Guide methods. In addition, five simply supported and five two span
deep beams were designed, fabricated and load tested to failure in an effort
to enrich the data base of deep beam test results as well as to ascertain the
applicability of CFP method in the design of deep beams. From the investigation it has been found that
shear failure is common in all the cases of deep beams. Whereas, clear
span-to-effective depth ratio has demonstrated insignificant effect, shear
span-to-effective depth ratio has been found to be a governing parameter in
controlling the shear strength. Vertical web reinforcement, strength of
concrete and amount of flexural steel have shown some influence on the shear
strength of concrete and amount of flexural steel have shown some influence
on the shear strength. It also appeared that the effect of horizontal steel
is much less than what is usually considered. Again, inclined cracking
strength has little influence on the
shear strength of such type of beams. The ACI code and CIRIA guide have
failed in predicting the ultimate strength of deep beams. Although, in most
cases, the CFP method predicted such strengths of deep beams more closely, as
the shear span-to depth ratio gradually decreases from 1.0, this method becomes
progressively conservative. Among other findings, it has been gathered that
the results obtained from tests of simply supported beams may not be applied
to continuous deep beams and that further tests on multi-span beams are
essential. |
|
Thesis
Title |
PUNCHING SHEAR BEHAVIOUR OF REINFORCED
CONCRETE SLABS |
|
Name
of the Student |
A. K. M. Jahangir Alam |
|
Supervisor Department |
Dr. Salek M. Seraj Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. September,
1997 |
|
Abstract |
Punching shear is an important consideration
in the design of reinforced concrete flat plates, flat slabs and column
footings. Present design rules for punching shear failure of reinforced
concretes slabs, given in various Codes of practice, are largely based on
studies of the behaviour and strength of simply-supported, conventional
specimens extending to the nominal line of contraflexure. As punching shear
provisions incorporated in various Codes of practice are a direct result of the
empirical procedures, they do not usually provide anaccurate estimate of the
ultimate punching load capacity of a slab with its edges restrained against
rotation. This is because no direct account is taken of the significant
enhancement of punching capacity due to the in-plane restraint in many types
of reinforced concrete slab systems. The present study describes punching tests
conducted on reinforced concrete slabs with their edges restrained as well as
unrestrained. Here, edge restraint has been provided, by means of edge beams
of various dimensions, to mimic the behaviour of continuous slabs. A total of
16 model slabs have been tested in an effort to ascertain the influence of
the degree of boundary restraint, percentage of steel reinforcement, and slab
thickness of the slab models on their structureal behaviour and punching
load-carrying capacity. The cracking pattern and load-deflection behaviour of
the slabs tested have also been monitored closely. The test program was
carried out to provide basic information on the real punching behaviour of
restrained slabs subjected to concentrated loading and may also be usefully
applied in the assessment of existing structures with laterally restrained
slab construction. The significant positive effect of edge restraint
on the punching failure load, resulting in enhancing the ultimate punching
strength, has been noticed. The code-specified strength of the specimens was
calculated in accordance with the American, British, Canadian and European
codes. It became apparent that no code-specified method predicts an
enhancement in the punching shear strength of a restrained reinforced
concrete slab with an increase in the degree of such restraints. Present
Codes do not recongnize the role of percentage of longitudinal steel on the
punching strength effectively either. It has been understood that inclusion
of the findings of the study in the design Codes will result in a rational
design of structural systems where punching phenomenon plays a vital role. |
|
Thesis
Title |
REAPPRAISAL OF CODE PROVISIONS FOR STRUCTURES
SUBJECTED TO SEISMIC LOADING |
|
Name
of the Student |
Munaz Ahmed Noor |
|
Supervisor Department |
Dr. Salek M. Seraj Associate Professor Department of Civil Engineering, BUET, Dhaka And Dr. Mehedi A. Ansary Assistant Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. September,
1997 |
|
Abstract |
Seismic code provides criteria for the design
and construction of new buildings subjected to earthquakes in order to
minimize the hazard to life for all buildings, to increase the expected
performance of higher occupancy structures as compared to ordinary
structures, and to improve the capability of essential facilities to function
after an earthquake. In the present study, efforts have been made to
critically evaluate seismic code provisions and identify areas in which
investigations could be carried out to update the code provisions. Efforts
have been made to formulate response spectra, which may be used in dynamic
analysis. A suitable numerical coefficient have been derived from these
response spectra for using in equivalent static analysis. Response spectra
have been formulated using four soil types from rock to soft. For the
development of the response spectra, several recent free field earthquake
records have been used. In absence of free field earthquake records,
earthquakes are simulated taking the appropriate properties of soils into
consideration. To incorporate the effect of soil and the effect of
attenuation in simulated earthquakes Kanai-Tajimi power spectra and
Shinozuka-Sato (1967) envelope have been incorporated in the available
subroutines. Performance of the developed spectra have been tested against
Uniform Building Code (1994) spectra by analyzing various moderately high
moment resisting framed structures. Additionally, a limited study has been
conducted to calculate the predominant time period for Dhaka City soil to
validate the applicability of the proposed simulated response spectra for
Dhaka City soils. It has been found that for calculating the
base shear in the equivalent static method, almost all codes of practice
adopt similar definitions for the various numerical coefficient of the base
shear formula. It appears that further improvement in the equations pertaining
to the calculation of time period of the buildings may not be rewarding. It
has been found that the maximum amplitude of the acceleration spectra
decreases as the soil changes from rock to soft type. It has been observed
that largest amplification occurs at the vicinity of natural time period of
soil. It has also been noticed that the rate of attenuation of rock spectra
was faster than stiff soil spectra. Rate of attenuation of the spectra
developed on the basis of recent free field earthquake records has been found
to be faster than the spectra embodied in the present day codes. It is
understood that efforts should be made to increase the value of structural
damping so that amplification of seismic forces is less. It is imperative to
install suitable number of seismic stations in Bangladesh so that local
spectra based on site specific real earthquake records can be developed. |
|
Thesis
Title |
PUNCHING BEHAVIOUR OF FOOTINGS |
|
Name
of the Student |
Md. Golam Mostafa |
|
Supervisor Department |
Dr. Salek M. Seraj Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. 1997 |
|
Abstract |
Punching shear is an important consideration
in the design of flat plates, bridge decks, column footings and mat
foundations. Present design rules for punching shear failure of reinforced
concrete slabs and footings, given in various codes of practice, are largely
based on studies of the behaviour and strength of simply supported,
conventional specimens extending to the nominal line of contraflexure. As
punching shear provisions incorporated in various Codes of practice are a
direct result of the empirical procedures, they do not usually provide an
accurate estimate of the punching load capacity of a slab with lateral
restraint. Again, present codes indiscriminately use equations, base on
punching test conducted on slabs, for the design of footings and mat
foundations. More importantly, a majority of the present codes usually
represent punching shear strength merely as a function of concrete
strength and ignores the possible
effects of percentage of steel, span to depth ratio, etc. The present study describes punching tests
conducted on eighteen footings, seventeen of which rested on sand. During
tests, percentage of steel reinforcement, depth, size and concrete strength
of model footings, as well as punching area were varied. Again, the rate of
loading as well as the degree of saturation of sand have been varied. The
test program was carried out to provide basic information on real punching
behaviour of footings subjected to concentrated loading. The punching strength of footings resting on
sand have been found to be significantly higher than the predictions of
present design provisions. The code-specified strengths of the specimens were
calculated in accordance with ACI 318-95, BS 8110-85, CAN3-A23.3-M84, CEB-FIB
and BNBC codes. It appears that no code specified method adequately caters
for the effect of the upward soil pressure on the punching strength of
footings. Most of the codes do not recognize the role of percentage of
longitudinal steel, on the punching strength either. The overall footing size
has been found to have very little effect on the punching strength of
footings. Since pressure distribution under a footing is expected to vary
depending upon soil type, the code provisons for footings should address this
issue faithfully to arrive at a realistic prognosis. During the course of the
investigations it became apparent that the concrete strength has a very
positive influence on punching strength of footings, as has already been
recognized in the codes. The effect of concrete strength, however, becomes
almost insignificant as the compressive strenth of concrete reaches high
values. The present series of tests confirmed, albeit tentatively, that the
presently adopted code methodology, where thickness has been considered to
have a linear contribution towards the punching strength, may be considered
to be valid. Rapid load tests conducted on footings resting on saturated sand
demonstrated that the difference between experimental failure load and code
predictions narrows down as the punching loads are applied at a very fast
rate, in comparison to its normal rate counterpart. It has been understood
that inclusion of the tenets of the thesis in the design Codes will result in
an economic and rational design of footings where punching phenomenon plays a
vital role. |
|
Thesis
Title |
A STUDY ON CEMENT AND LIME STABILISED
CHITTAGONG COASTAL SOILS FOR USE IN ROAD CONSTRUCTION |
|
Name
of the Student |
Bipradas Rajbongshi |
|
Supervisor Department |
Dr. Abu Siddique Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. December,
1997 |
|
Abstract |
In the present study, cement stabilization of
two selected soils (collected from Anwara and Banshkhali) and lime
stabilization of a soil (collected from Banshkhali) of Chittagong coastal
region were carried out in order to assess their suitability for use in road
construction. The soils from Anwara and Basnkhali were respectively a clayey
silt of low plasticity (LL = 30, PI = 7) and a silty clay of medium
plasticity (LL = 44, PI = 19). As additives, ordinary Portland cement was
used in percentages of 1, 3 and 5 while slaked lime was used in 3%, 5% and
7%. Analytical works using CIRCLY computer program were also undertaken in
order to determine the thickness of cement stabilised bases and lime
stabilised sub-bases of rural roads in the coastal region. Index tests indicated that compared with the
untreated samples, plasticity index and linear shrinkage of the cement and
lime stabilised samples of the soils reduced. Shrinkage limit, however,
reduced for cement-treated samples while it increased for lime-treated
samples. For the cement and lime stabilised samples, maximum dry density
increased and reduced respectively, while optimum moisture content reduced
and increased for cement and lime stabilized samples respectively with the
increase in additive content. For samples of both the coastal soils,
compared with the untreated samples, unconfined compressive strength (qu)
of cement and lime treated samples increased significantly, depending on the
additive content and curing age. It was found that compressive strength of
samples treated with 3% and 5% cement and cured for 14 and 28 days satisfied
the requirements of PCA (1956) for the compressive strength of soil-cement
mix and that for all cement contents and all curing ages, compressive
strength of the stabilised samples fulfilled the requirements of soil-cement
mix for use in road sub-base and base subjected to light traffic, as proposed
by Ingles and Metcalf (1972). It was also found that the compressive strength
of samples treated with 5% and 7% lime met the requirements for upgrading
heavy clays to sub-base material quality type, as proposed by Ingles and
Metcalf (1972). In an attempt to investigate the effect of moulding water
content on qu, it appeared that in order to achieve maximum
compressive strength, the cement and lime stabilized samples should be
compacted at their optimum moisture content respectively. Compared with the
untreated samples, CBR of the cement and lime stabilized samples increased
considerably. It was found that CBR-values of cement and lime stabilised
samples increased up to about 5 times and 3 times respectively. CBR-values of
samples of both the soils, treated with 3% and 5% cement, fulfilled the
requirements of soil-cement road sub-base for light traffic while CBR of
sample stabilised with 7% lime did not satisfy the criteria of the minimum
CBR for soil-lime mix for improvement of base material in road construction,
as proposed by Ingles and Metcalf (1972). The flexural stress versus deflection curves
have been found to be approximately linear for both cement and lime
stabilised samples. Compared with the untreated samples, flexural strength
and flexural modulus of the cement and lime stabilised samples increased
considerably, depending on the additive content. Compared with the untreated
sample, the flexural strength and flexural modulus of cement-treated samples
increased up to about 6 times and 4.3 times while for lime-treated samples
the respective increases were about 2 times and 2.25 times. The loss in
soil-cement of cement-treated samples reduced with the increase in cement
content. Although, the cement-treated samples did not meet the PCA (1956)
durability requirements, the samples treated with 3% and 5% cement, however,
fulfilled the requirements as suggested by Compendium 8 (1979). It was found from comparisons that the values
of qu, CBR, flexural strength and flexural modulus of the
cement-treated samples of Banshkhali were significantly higher than those of
the lime-treated samples. Moreover, it is expected that compared with
soil-lime mix, soil-cement mix would be much more durable in the weather
conditions of tropical regions. It could be concluded that cement
stabilisation of the coastal soils studied would be more suitable than lime
stabilisation for their use in road construction. Analytical results indicated that at a
particular modulus and CBR, the thicknesses of soil-cement base (for both
unpaved and paved road) and soil-lime sub-base increased with increasing
allowable number of load repetitions to fatigue (N) and that for any
particular value of N, the values of thicknesses of soil-cement base (for
both unpaved and paved road) and soil-lime sub-base reduced as modulus of
soil-cement base and soil-lime sub-base increased. Design charts have been
developed for the three types of roads analysed and it has been found that,
in general, at any CBR and N, the thickness of cemented layer reduced as
modulus of the cemented layer increased. |
|
Thesis
Title |
|
|
Name
of the Student |
Md. Mokhlesur Rahman |
|
Supervisor Department |
Dr. Abu Siddique Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. September,
2000 |
|
Abstract |
The present study has been carried out to
investigate the effect of sampling disturbance on mechanical behaviour of reconstituted normally consolidated and overconsolidated Dhaka clay (OCR
values of 2, 5 and 10).. Disturbed Dhaka clay samples were collected from
Rupnagar Housing Project, Mirput-11, Dhaka. The clays were low to medium
plasticity (LL= 47, PI= 26). Reconstituted normally consolidated samples of
Dhaka clay were prepared in the laboratory by K0-consolidation of
slurry in a large cylindrical consolidation cell using a consolidation
pressure of 150kN/m2 while overconsolidated samples having OCR
values of 2, 5 and 10 were prepared
by reducing the maxmimum pressure of 150 kN/m2 to 75 kN/m2,
30 kN/m2 and 15 kN/m2 respectively. “In situ” samples
were prepared (by consolidating 38 mm diameter by 76 mm high specimens under
K0-conditions in the triaxial cell) to its “in situ” stress state.
“Tube” samples of various OCR values were prepared from the large diameter
consolidated sample by inserting samplers of different area ratio, external
diameter to thickness ratio (De/t) and outside cutting edge angle
(OCA). The area ratio, De/t ratio and OCA of the samplers varied
from 16.4% to 73.1%, 27.3 to 8.3 and 5°
to 20°
respectively. Normally consolidated and overconsolidated “perfect” samples
were prepared from respective “in situ” samples by undrained release of the
total stress in the triaxial cell. Undrained triaxial compression tests were
carried out on “in situ” “tube” and “perfect” samples. “Tube” and “perfect”
samples having OCR values of 2 and 10 were also reconsolidated isotropically
and anisotropically under K0-condition using BjerrUM (CKoU-1.0s¢vc) and SHANSEP
(CKoU -1.5s¢vc
and (CKoU -2.5s¢vc)
procedures. Disturbance due to perfect and tube sampling
have significant influence on the mechanical properties of normally
consolidated and over consolidated Dhaka clay. Disturbance due to perfect
sampling led to reduction in the value of su and Ap
while Ei, E50 and
ep
increased caused due to total stress relief. Because of perfect sampling
undrained strength (su) reduced up to 8.2% while, axial strain at
peak deviator stress (ep)
increased up to 20.9% for samples of OCR value of 10. Due to perfect sampling
pore pressure parameter at peak deviator stress (Ap) reduced up to
90% while, initial tangent modulus (Ei) and secant stiffness at
peak half deviator stress E50) increased up to 14.0% and 19%
respectively for normally consolidated sample. Due to total stress relief for
perfect sampling disturbance, the reduction in su increases with
increase in OCR while, the increase in Ei, E50 reduce
with increase in OCR. The initial effective stress (s¢i) of “tube”
samples reduced considerably because of disturbance caused by penetration of
tubes. Compared with “in situ” samples, values of su, Ei,
E50 and Ap of the “tube” samples reduced while
ep increased. Changes in measured soil
parameter between the “in situ” and “tube” samples have been found to depend
significantly on the sampler characteristics (area ratio, De/t
ratio and OCA) used for retrieving the “tube” samples. The values of
s¢i, su,
and Ei were reduced up to 26.2%, 43% and 62% respectively for
normally consolidated sample due to increase in area ratio from 16.4% to
73.1% (or reduction in De/t ratio from 27.3 to 8.3). The
respective reductions for normally consolidated sample due to increase in OCA
from 4°
to 15°
are 21.9%, 38% and 60%. Values of
ep
for OCR values of 1 and 5, increased up to 57.7% and 52.6% due to increase in
area ratio and OCA respectively. A quantitative increase in the degree of
disturbance (Dd) has been obtained due to increase in area ratio
and OCA. The results indicate that compared with normally consolidated
reconstituted Dhaka Clay, tube sampling causes relatively little degree of
disturbance in overconsolidated reconstituted Dhaka Clay. The reduction in
initial effective stress due to tube sampling reduces with increase in OCR.
The increase in value of
ep
due tube sampling reduce with increasing OCR. For tube sampling disturbance,
trend of small decrease in the reduction of su/s¢vc, E i/s¢vc and E 50/s¢vc was obtained
with increasing OCR. However, significant increase in reduction of Ap
with increasing OCR also been observed. It appeared that for good quality sampling, a
sampler ought to have a well combination of area ratio and OCA. In order to
reduce disturbance due to sampling in soft Dhaka clay, are ratio and OCA of
sampler should be kept practically as low as possible. A correction curve has
been provided from the plot of strength ratio versus overconsolidation ratio
for samples of Dhaka clay. This correction curve can be used to find the
perfectly undisturbed strength of the tube samples of Dhaka clay for use in
analyses and designs. Isotropic reconsolidation (CIU-1.0s¢vc) has the
effect of gross overestimation of “in situ” strength,
ep
and Ei for the “tube” and “perfect” samples. It has been found
that compared with SHANSEP procedures reconsolidation using Bjerrum procedure
(CKoU-1.0s¢vc)
for both “tube” and “perfect” samples of overconsolidated Dhaka clay,
produced the best overall estimate of the “in situ” properties in terms of
undrained strength, stiffness, strain and pore pressure response. |
|
Thesis
Title |
GEOTECHNICAL CHARACTERIZATION OF DHAKA
METROPOLITAN AREA |
|
Name
of the Student |
Md. Abul Bashar |
|
Supervisor Department |
Dr. Abu Siddique Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. July,
2000 |
|
Abstract |
The present study has been carried out to
develop generalized soil profiles of Dhaka Metropolitan area. Attempt has
been made to investigate the variation of the soil properties with depth and
to establish approximate correlation among different geotechnical properties
of the sub-soil of the Dhaka Metropolitan Area. Attempt has also been made to
verify the existing soil data by drilling a number of test bore holes. About 300 sub-soil investigation reports
consisting of data of 674 boreholes were collected from different drilling
companies, civil consulting firms and other organizations of different places
of Dhaka Metropolitan Area. Majority of the borings were drilled up to depth
of 50ft to 60ft and a feew borings were drilled up to 100ft. Dhaka city map,
bounded by longitude 90°20¢ to 90°27¢E and 23°41¢ to 23°53¢N, has been
divided into grids by four by longitudinal grid lines long North-South
direction and five cross grid lines along East-West direction. These grid
lines were spaced at 2 minutes interval. All borehole site location points
were inserted on the Dhaka city map. One site location point consists of
multiple number of boreholes. Under the scheme of the research, seven test borings of 100 ft
depth were drilled in the vicinity of the grid points. Soil profiles established for Dhaka
Metropolitan area, in general, showed soft to very stiff cohesive layers at
the top strata up to depth of 20 ft. At large depths, the soil layers have
been found to consist of loose to very dense sandy soils. In some areas of
the eastern region of Dhaka Metropolitan, However, cohesive layers up to
depth of 100ft have been encountered. Range of the values of different soil
parameters near the locations of sixteen grid points of Dhaka Metropolitan
area has been summarized. The soil parameters considered are N-value, liquid
limit, plasticity index, natural moisture content, grain size fractions
(percentages of sand, silt and clay), unconfined compressive strength,
compression index (Cc) and initial void ratio. Geotechnical
properties of the sub-soil of Dhaka metropolitan area were found to vary with
depth. In general, water content, liquid limit and plasticity index decrease
with the increase in soil depth. The percentage of coarser material increases
with the increase in soil depth. The relationship between unconfined
compressive strength (qu) and standard penetration resistance (N)
can be expressed as qu = N/2.77 ksf. It has been found that the
proposed relation between qu and N for Dhaka clay samples compared
favourable with the correlation proposed by other researchers. The relation
between plasticity index and liquid limit for the cohesive soil samples of
Dhaka Metropolitan area showed that majority of the samples are clays of low
to medium and medium to high plasticity. A few samples were, however,
cohesive silts. A trend of decrease in unconfined compressive strength with
the increase in natural water content has been observed while an increase in
the value of compression index with the increase in initial void ratio (e0)
was found for samples of Dhaka Metropolitan area. A trend of increase in the
value of the ratio Cc/(1+e0) with the increase in
natural moisture content value has been observed for samples of Dhaka
Metropolitan area. No conclusive relation could not be found between
compression index and plasticity index for samples of Dhaka Metropolitan
area. The collected soil data were compared with
those obtained from the test boreholes in order to verify the available type
of strata and N-values. In a number of locations, the soil profile and
N-values obtained from the test boreholes compared favourably with those
obtained from the available borehole data drilled in the vicinity of the test
boreholes. In some locations, however, the soil profile and N-values obtained
from the test boreholes were different from those obtained from the available
boreholde data drilled adjacent the location of test boreholes. |
|
Thesis
Title |
INFLUENCE OF STRUCTURE PARAMETERS ON PERIOD OF
FRAME STRUCTURES FOR EARTHQUAKE RESISTANT DESIGN |
|
Name
of the Student |
Md. Zahid Hossain |
|
Supervisor Department |
Dr. A. M. M. Taufiqul Anwar Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. January,
1997 |
|
Abstract |
Codes of practice suggest equivalent static
force method for earthquake resistant design of frame structures of moderate
height. For regular frames, the codes propose approximate formulae for
fundamental period required for the evaluation of base shear. These formulae
describe period either as a function of height of the structure or number of
stories. Lack of reflection of other structure parameters makes them grossly
approximate. An investigation is conducted in this work to assess the
influence of different structure parameters on the period of regular frame
structures. Model frames, divided into six major groups are subjected to
modal analysis to evaluate the fundamental frequency and corresponding
period. General purpose finite element package ANSYS, Revision 5.2, has been
employed to conduct the analyses. The analysis tool assumes constant
stiffiness and mass effects and neglects damping. Appropriate elements are
selected from ANSYS element library to model the frames. ANSYS option of
lumped mass approach has been used for mesh elements. Masses of secondary
structures are added as point mass elements at nodal points. Modal analysis
has been used as analysis type and reduced method as analysis option. The
extracted eigenvaleus and the corresponding eigenvectors represent the
frequencies and mode shapes respectively. The fundamental period is obtained
from the lowest frequency. An extensive parametric study is conducted to
identify influence of parameters like numbers and width of bays, numbers and
height of stories, stiffiness of columns and beams and strength and density
of concrete on fundamental period. Effect of inclusion of floor slabs and
masses of secondary structural elements in the analysis is also studied. The
period has been found to increase with decreasing number of bays along the
direction of motion or increasing number of bays transverse to the direction
of motion. An increase of bay width, story height or number of stories leads to an increase of period.
Approximate code formulae are found to become increasingly conservative with
increasing structure height in evaluation of earthquake forces. Use of stiffer columns and beams or concrete
of higher strength has a reducing effect on period. It has been revealed that
application of approximate code formulae in cases of low rise structures with
stocky columns and beams or with concrete of higher strength may lead to an
understimation of earthquake forces. A reduction in beam height or column
dimension in the direction of earthquake forces or choice of low strength
concrete are found to reduce design earthquake forces. In most practical
cases, the approximate code formulae lead to a conservative estimation of
earthquake forces. |
|
Thesis
Title |
|
|
Name
of the Student |
Hafiz Ahmad |
|
Supervisor Department |
Dr. A. B. M. Badruzzaman Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. February,
1998 |
|
Abstract |
The primary objective of this study was to
assess the level of copper contamination in the lake water and sediment of
Dhanmondi and Ramna Lakes. The other major objectives were determination of
equilibrium speciation of copper in lake water in order to assess its toxic
effects, determination of spatial distribution of major copper species,
evaluation of copper adsorption characteristic on different sizes of bed
sediment particles of both the lakes and assessment of gross bioaccumulation
of copper in fish. Water and sediment samples of Dhanmondi and
Ramna lakes were collected from different sampling locations for laboratory
analysis during three different periods of the year namely, dry period (April
to May), wet period (June-July) and intermediate period (August-January).
Sediment samples were collected to assess the nature of copper adsorption on
the bed sediment particles. In addition, bioaccumulation of copper in fish of
the lake was assessed by determining copper concentrations in various parts
including gill, stomach etc. of a fish (Nilotica) of Dhanmondi lake. Both the Dhanmondi and Ramna lake water and
sediment layers were found to be heavily contaminated with copper. Maximum
and minimum concentrations of copper in the water of Dhanmondi lake was
0.2913 mg/1 and 0.062mg/1 and in Ramna lake 0.2047 mg/1 and 0.0723mg/1,
respectively. Major aqueous copper species found in both the Dhanmondi and
Ramna lakes were Cu(OH)2, Cu2+, CuCO3,
concentration of Cu(OH)2 was maximum. Cu2+, the free
and most toxic form of copper species was also present in considerable
amounts. pH was found to be the major controlling factor for copper
speciation. With a decrease in pH, ionic copper (Cu2+) concentration
increase thus increasing the toxicity of water. Conversely, with an increase
in pH, ionic copper concentration decreases with increased adsorption
reducing toxicity. Analysis of sediment samples suggest that
maximum amount of copper was adsorbed on particles retained on sieve # 30, #
40, # 50 (i.e. size <1.19mm to >0.297mm). In most cases, copper
absorption increased with the decrease in particle size upto a certain level
(0.42mm). After that particular particle size copper absorption decreased
with the decrease in particle size. From the analysis of bed sediment it was
found that maximum copper concentrations in top and bottom layers of
Dhanmondi lake were 59.45 mg/kg and 52.28 mg/kg, respectively. In Ramna lake
copper concentration in top and bottom layers were 47.77 mg/kg and 46.21
mg/kg respectively. Study of bioaccumulation of copper revealed
that copper is present in excessive amount in the different parts of fish in
Dhanmondi lake. Maximum copper concentration was found in the stomach (7.442
mg/kg) of fish. Thus, human consumption of the fishes from Dhanmondi lake may
be harmful. At persent renovation work is underway at the
Dhanmondi lake. It seems that the lake is dredgedbridged indiscriminately and
the dredged spoils are being piled along the shore. If not done upto a proper
depth this dredging process is likely to expose the soil layer heavily
contaminated with copper. (The ovelying fresh water way be contanuinated
through)diffusion and desorption from the newly exposed bed. In addition, the
dredged spoils piled along the shore may release copper following rainfall
into the lake and surrounding areas. |
|
Thesis
Title |
PERFORMANCE OF THE EXISTING SEWERAGE SYSTEM OF
DHAKA CITY AND PAGLA SEWAGE TREATMENT PLANT |
|
Name
of the Student |
Md. Naziruzzaman |
|
Supervisor Department |
Dr. A. B. M. Badruzzaman Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. July,
1999 |
|
Abstract |
The sewerage system of Dhaka city was
initiated in 1923 with about 50 km sewer lines and an imhoff tank type
treatment plant. Till to date about 531 km sewerage network, 20 sewage lift
stations have been developed in different phases at different times to keep
pace with the expansion of the city. The first conventional sewage treatment
plant with 4 facultative lagoons built at Pagla in 1968 was renovated in
1977. The present sewage treatment plant at Pagla was rehabilited and
expanded in 1992 to treat a capacity of 120,000 m3/day sewage with
influent BOD5 of 200 mg/1 and effluent BOD5 of 50 mg/1. About 150,000m3/day wastewater is
presently being generated within the sewerage covered area of which only 28%
find it’s way to reach Pagla sewage treatment plant. Remaining 72% of sewage
generated is discharged to the environment through leakages, overflows, etc.
of the network, creating tremendous pollution, hence affecting the human
health. From the study it is found that under present situation about 50% of
the city sewerage network is undersized, a large portion of the trunk mains
are in low lying areas without service road. Some portion of the sewer mains
is under the roads or even under structures. In addition, the sewer mains
have construction defects like frequent improper sewer gradients, syphones,
etc. Due to the defective construction of sewers manholes always remain
flooded with several feet of wastewater. In this study, it is also observed
that there are several leakages in the sewerage network including completely
blocked manholes. The outlet sewer of the Dhaka Medical College sewage lift
station is broken and sewage is being pumped into the nearby surface drain.
Most of the sewage lift stations were constructed or designed in such way
that the back-flow/submersion of intake frequently takes place with
subsequent septic condition in the sewage. This is one of the major reasons
for high BOD5 value. Pumps of the sewage lift stations are very
old and needs frequent repair. An average of 28% (43,000 m3/day)
of generated wastewater is being treated by the Pagla Sewage Treatment Plant
(PSTP) at present. From the study it is found that the performance of the
primary sedimentation tanks are acceptable and that of facultative lagoons
are not satisfactory. The influent BOD5 value of the sewage
treatment plant is as high as 4,100 mg/1, which was designed for a influent
BOD5 value of 200 mg/1. The effluent BOD5 value is much
higher, some 240 mg/1 instead of designed value of 50 mg/1. The observed
effective sewage depths of the lagoon are around 1.0m though these were
designed for an effective sewage depth of 2.0m. On the bottom of the lagoons
about 0.30m height of suspended solids found to have settled. The laboratory
of the treatment plant is not well equipped to conduct regular monitoring.
The sludge lagoons are functioning well and are in good condition. There
exists a liquid chlorination system at the outlet of the plant with a dosing
of 3.0 ppm and performing twice a day from 6 A.M. to 9 A. M. and 2 P. M. to 4
P. M. For the improvement of the sewerage system,
rearrangement and redesign is recommended. Moreover, the entire Dhaka City
should be covered under sewerage system. It is also recommended to
specifically identify the reasons of the high BOD5 value in the
sewage including a proper inventory of effluent quality, discharge points,
etc. of different industries. Change of old pumps of the sewage lift stations
with suitable new ones like variable speed pumps may be introduced to
overcome the problems of the lift stations. |
|
Thesis
Title |
ANALYSIS OF HEAVY METALS IN BED SEDIMENTS OF
DHANMONDI LAKE |
|
Name
of the Student |
Khandaker Nurul Ashfaque |
|
Supervisor Department |
Dr. A. B. M Badruzzaman Associate Professor Department of Civil Engineering, BUET, Dhaka |
|
Degree
and Year of Published |
M. Sc. Engg. November,
1999 |
|
Abstract |
The Dhanmond Lake, the largest urban lake of
the Dhaka City, has been receiving domestic as well as industrial sewate for
a long time. The primary objective of the study was to assess the heavy metal
contamination of the sediment column of Dhanmondi Lake at different
locations. Secondary objectives include the determination of any possible
relationship between metal concentration with particle size, vertical
distribution of metal, assessment of association of metal with the organic
and inoraganic fractions and estimation of partition coefficient of a
specific heavy metal. Sediment samples from ten locations of
Dhanmondi Lake were collected from various depths. Locations were selected
considering the probable sources of contamination from sewer lines connected
to the Lake. In general, the soil samples were found to be grayish to black
in color indicating high organic content. This can be attributed to disposal
of domestic and industrial sewage. However, at greater depths reddish silty
clay soil’ were distinctly visible which represent the original bed soil of
the Lake. Samples were oven dried, ground and sieved. Then the samples were
digested and the concentrations of different heavy metals (copper, lead,
cadmium, chromium and mercury) at different depths were determined for each
particle size using an Atomic Adsorption Spectrometer. The general trend of copper distribution
associated with particle sizes indicates that the copper concentration
increases with the decrease of particle size up to 0.30mm, then it decreases
with the decrease in particle size ranging between 0.30mm to 0.15mm. This
trend changes again and the copper concentration increases with decrease in
particle size. In case of lead, the concentration increases with the decrease
in particle size upto 0.15mm. Then it decreases with the decrease in particle
size of 0.15-0.075mm. Finally, it increases slightly with the decrease in
particle size. No general pattern of cadmium distribution with particle size
has been observed. However, test results indicate that higher cadmium concentration
is associated with particle size between 0.6-0.3mm at all locations
irrespective of depth. Concentration distribution of chromium with particle
sizes generally followed two distinct patterns: (a) chromium concentration
increases upto 0.15mm particle size, then decrease for particle sizes
0.15-0.075mm and then increases again; (b) chromium concentration decreases
upto 0.075mm particle size and then increases. However, in both of the
patterns the lowest cadmium concentration was found to be associated with
particle sizes of 0.075mm. Mercury is probably the most toxic metal
available in the environment even at very low concentrations. But due to lack
of resources very limited number of samples were tested for the presence of
mercury. Vertical distribution of mercury concentration as well as those of
other metals indicated a higher level near the bed surface, which
subsequently decreased as the depth increased. Samples collected from near
the Pikhana BDR Gate exhibited highest concentration for all metals among all
the locations. However, the average concentration level throughout the lake
sediment is alarming. The laboratory results indicate that the major
fractions of the heavy metals are associated with the organic fraction of the
soil. However, it should be noted that during washing of the samples to
separate organic fraction using NaOH, a significant portion of iron (oxy)
hydroxides (and probably some other oxide particles as well), which provides
the surface for adsorption of heavy metals on sediments, might have been
washed out from the inorganic fraction. In general, the heavy metal
concentration was found to increase with the increase in organic content. In
order to estimate the partition coefficient of a specific heavy metal, a
synthetic sample was prepared in the laboratory and was dosed with different
metal solutions. The analysis of the synthetic sample does not provide any
conclusive evidence. This may be attributed to the fact that the synthetic
samples were analyzed only 72 hours after dosing which might not have given
enough time to allow proper adsorption of all metals. Also, the chemical
composition of the synthetic soil sample might have been different than that
of bed sediment of Dhanmondi Lake. At present, the restoration work of the Dhanmondi
Lake is in progress. A massive excavation campaign was conducted to remove
the contaminated bottm sediment. At
some locations the excavation was carried out to reveal the original
formation. However, at most of the places this was conducted to partially
remove the contaminated soil leaving the highly contaminated soild layer
exposed to the fresh water to be introduced. This will definitely pollute the
overlying water layer. In addition, these excavated contaminated soils were
used for landfilling purposes within the city areas leaving the population
and aquatic biota susceptible to heavy metal pollution. |