Pollutant Dispersion Characteristics in Dhaka City, Bangladesh

Khandaker M. A. Hossain,Said M. Easa 한국기상학회 2012 Asia-Pacific Journal of Atmospheric Sciences Vol.48 No.1

Air pollution is a major environmental concern in major cities around the world. The major causes of air pollution include rapid industrialization/urbanization and increased non environmentfriendly energy production. This paper analyses the atmospheric pollutant such as carbon monoxide (CO) and particulate matter (PM)dispersion characteristics of Dhaka city. The yearly and diurnal variations of pollutant concentration are described by taking into consideration of both meteorological and emission source parameters highlighting washout effect due to rainfall and inversion phenomena. Concentration of PM (both PM2.5 and PM10) and CO in the ambient air are measured for a period of one year with Airmetric Minivol air samplers and Gas Chromatographic (GC) technique, respectively. The trend over the year shows an increase in the monthly average hourly PM and CO concentrations in winter months (November to March)when both PM10 and PM2.5 annual average concentrations (about 130 and 95 μgm−3, respectively) exhibit levels exceeding World Health Organization (WHO) guidelines as well as exceed more than twice the national standards of annual PM10 (50 μg m−3) and PM2.5 (15μg m−3) concentrations. Such high pollutant concentrations may have significant health implications for residents of Dhaka city. It is also found that the PM concentration increases with the increase of wind speed during dry winter season and is also influenced by transboundary air pollution. The data and subsequent recommendations can be useful in formulating air quality management strategies for the Dhaka city.

Modeling of Unsymmetrical Single-lane Roundabouts based on Stopping Sight Distance

Said M. Easa 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.2

Evaluation of the adequacy of sight distance at roundabout is usually performed graphically as no quantitative guidelines are available for the lateral clearance needs. This paper presents analytical lateral clearance models to satisfy Stopping Sight Distance (SSD) at unsymmetrical single-lane roundabouts (with different entry and exit radii). The models are developed for three critical locations: approach sight distance, sight distance to exist crosswalk, and circulatory roadway sight distance. Two cases of approach sight distance are presented: sight distance to the crosswalk and sight distance to the yield line. The required lateral clearance at any specified point along the curve can also be determined. Design aids for the required maximum lateral clearance are established for the three locations of sight distance based on accurate SSD formula that accounts for effect of the radial deceleration component of the vehicle. For the circulatory roadway sight distance, infeasible combinations of the circulatory roadway radius and speed are identified based on acceptable driver’s field of peripheral vision. The models and results of this paper, which are applicable to both symmetrical and unsymmetrical roundabouts, should be of interest to highway engineers and designers.

New Open Channel with Elliptic Sides and Horizontal Bottom

Said M. Easa,Ali R. Vatankhah 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.4

This paper presents a new general open channel section with elliptic sides and horizontal bottom. The proposed section producesspecial channel forms, such as a circular section with a horizontal bottom, a circular section, and a rectangular section. Exact andapproximate formulas for the area and perimeter of the channel are derived. These formulas are then used to develop an optimizationmodel for determining the optimal section design that minimizes the total construction cost for excavation and composite linings. Inaddition, the most hydraulically efficient elliptic section was derived. The constraints of the optimization model include channeldischarge and physical requirements, such as flow depth, top width, and side slope with fixed or depth-dependent freeboard. The costperformance of the proposed section was compared with another general open channel section (power-law) and the trapezoidalsection using different design scenarios. The results show that the new section is substantially more economical and more flexiblethan the existing power-law section, and is generally superior to the trapezoidal section.

Evaluation of Nonlinear Muskingum Model with Continuous and Discontinuous Exponent Parameters

Said M. Easa 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.7

The nonlinear Muskingum model is traditionally calibrated using a constant exponent parameter. A recent study has proposed a discontinuous function of the exponent parameter that has substantially improved model performance. This paper evaluates model performance using continuous and discontinuous parameters, expressed as a function of dimensionless inflow variable. The parameters were represented by discontinuous (two-step) function and continuous (three-coefficient) function, resulting in a fiveparameter nonlinear Muskingum model (5P-NLMM) for each scheme. Two continuous functions (logarithmic and exponential) were evaluated using two flood routing procedures: the Modified Euler’s (ME) routing procedure and the Fourth-Order Runge-Kutta (FORK) routing procedure. The continuous functions and routing procedures were integrated into the Muskingum model. The five parameters of the model were determined using optimization based on minimizing the deviations from observed outflows. The model was applied to three examples with different hydrograph types. The continuous parameter (with ME or FORK) substantially outperformed the discontinuous parameter for smooth and non-smooth hydrographs, and vice versa for multi-peak hydrograph. Guidelines for model selection for different types of hydrographs are presented.

Versatile General Elliptic Open Channel Cross Section

Said M. Easa 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.4

This paper proposes a versatile open channel cross-section (or simply section) with General Elliptic (GE) sides and horizontal bottom. The GE section includes four parameters that provide more degrees of freedom to accommodate multiple physical constraints and produce better optimal solutions. The proposed section provides as special cases numerous sections such as elliptic, circular, triangular, trapezoidal, and rectangular. The dimensions of GE section that minimize construction cost of excavation and composite linings are determined using mathematical optimization. Constraints on channel discharge and geometry (e.g. flow depth, top width, and side slope) are included. The model was validated and its performance was compared with other known sections. The results show that the GE section improves construction cost by up to 10%-12% compared with the ordinary elliptic section which has been recently shown to outperform most known open channel sections.

Artificial neural network model for the strength prediction of fully restrained RC slabs subjected to membrane action

Khandaker M. A. Hossain,Mohamed Lachemi,Said M. Easa 한국계산역학회 2006 Computers and Concrete, An International Journal Vol.3 No.6

This paper develops an artificial neural network (ANN) model for uniformly loaded restrained reinforced concrete (RC) slabs incorporating membrane action. The development of membrane action in RC slabs restrained against lateral displacements at the edges in buildings and bridge structures significantly increases their load carrying capacity. The benefits of compressive membrane action are usually not taken into account in currently available design methods based on yield-line theory. By extending the existing knowledge of compressive membrane action, it is possible to design slabs in building and bridge decks economically with less than normal reinforcement. The processes involved in the development of ANN model such as the creation of a database of test results from previous research studies, the selection of architecture of the network from extensive trial and error procedure, and the training and performance validation of the model are presented. The ANN model was found to predict accurately the ultimate strength of fully restrained RC slabs. The model also was able to incorporate strength enhancement of RC slabs due to membrane action as confirmed from a comparative study of experimental and yield line-based predictions. Practical applications of the developed ANN model in the design process of RC slabs are also highlighted.

Soil Interaction of H-shaped Steel-RC Stepped Pile of Integral Abutment Bridge: Experimental Evaluation

Yizhou Zhuang,Kun-Sheng Song,Said M. Easa,Yong-Qing Song 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.3

The reinforced concrete piles (RC) in integral abutment bridges (IABs) are challenging to meet the longitudinal deformation of bridges with significant lateral stiffness. The H-shaped steel (HS) piles are costly and prone to corrosion. This paper proposes a new form of pile comprised of HS and RC piles in series to meet the longitudinal deformation demand of IABs. Tests were conducted for one HS pile under reciprocating low-cycle pseudo-static test and two HS-RC stepped piles with different bending stiffness ratios of HS/RC (0.25 and 0.5) using the HS-RC pile test model,. The influence of the stiffness ratio on the mechanical behavior of stepped pile-soil was studied. The mechanical behavior of the stepped pile was also compared with single HS and RC piles. and the applicability of the m and p-y curve methods to the calculation of horizontal displacement of stepped pile is discussed. The results show that the elastic deformation range of the HS pile is 2 mm to 25 mm, and its horizontal deformation capacity and bearing capacity are excellent. As the stiffness ratio increases, the stepped pile-soil system's yield displacement and yield load increased. The stiffness ratio has no significant effect on the failure mode of the piles. The hysteretic ring of the stepped pile shows a squeezing shape at the initial loading stage, but becomes a full spindle in the later loading stage. The stepped pile shows an excellent energy consumption effect and a horizontal deformation ability, indicating it is suitable for IABs. The m method has better accuracy only up to 2 mm displacement, while the p-y curve method still has higher accuracy within 15 mm.