9 Records out of 22207 Records

Performances evaluation of a subsurface horizontal flow constructed wetland in the tropics.

Author: Mburu, Njenga

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : MSc

Year: 2004

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ;

Subject Terms: Civil engineering ; Wetlands ; Hydrology ;

Abstract:

Pilot scale studies were conducted to determine the performance of a subsurface horizontal flow constructed wetland in the tropics in the period April to July 2003. The wetland located at Jorno-Kenyatta University of Agriculture and Technology sewage treatment works consisted of four cells set in parallel, each of 22.5m2. Three of the cells had gravel and in two of the cells with gravel the tropical macrophyte Cyperus Papyrus was introduced. The wetland received a continuous feed of settled sewage from a primary facultative pond at the treatment works. Performance of the wetland was evaluated in terms of removal of organic matter and suspended solids, nutrients and pathogenic bacteria. This was done under different operating conditions of pollutant loading and hydraulic loading rates Moderate removal rates of up to 50 % for organic matter (BOD5 and COD) and Total Suspended Solids (TSS) were obtained with an areal BOD5 removal rate constant of 0.0485 mid. The background or residual BOD5 determined for the vegetated wetland cells was 11 mgIL. The loading rates deduced from the study for BOD5 and TSS were 373 KglHa.d and 122 KglHa.d respectively. A retention time of 2 days was found to be optimum for BOD5 removal. Low removal of less than 30% was observed for nutrients. The vegetated wetland cells had better removal compared with the unvegetated cells implying an enhanced nitrification-denitrification path for nitrogen removal and plant uptake for phosphorus. Fecal coliform removal in the wetland of up to three log units was realized. The removal was found to -be influenced by the influent coliform count and not the hydraulic retention time. When fecal count in the influent was- within 2 log units 99.9 % removal was realized. These results indicate that the use of subsurface horizontal flow constructed wetlands for wastewater treatment in the tropics is feasible and holds great potential for improving the sanitation conditions in developing countries.

Flexural behaviour of large scale concrete elements reinforced with bamboo

Author: Maritim, Nelson Kipkemboi

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : MSc

Year: 2004

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ;

Subject Terms: Civil engineering ; Concrete ; Bamboo ;

Abstract:

This research study is on bamboo culms as an alternative material for concrete reinforcement in low cost housing. In this research the commonly found bamboo species in Kenya Arundiraria Alpina was used to reinforce concrete beams, which were then subjected to flexural test. Other tests like tensile, compression, shear, pull-out test of bamboo and steel in concrete were also done in order to understand the basic properties of bamboo as a reinforcement material. Various tests such as compression, tension splitting and flexural testing prisms were also conducted on the concrete, in order to ensure that the concrete used met the required standard. The strength tests of bamboo obtained and those of previous investigations carried out by other researchers depict bamboo to be a fairly strong material that can be used as a substitute for steel reinforcement. The mean tensile strength of seasoned bamboo is 197.61 Nzmm' and 251.28 Nzmm? for bamboo with and without nodes respectively. The average composite strength of bamboo reinforced concrete beams is 105.5 Nzmm- at 28 days, which is about a half the actual tensile strength of seasoned bamboo. The average Elastic modulus of bamboo is 23.31kN/mm2 for seasoned bamboo and the mean interfacial bond strength of quarter bamboo in concrete is 1.99 Nzmm? at 28 days, which is about 25 % that of structural steel in concrete, which was determined as 7.78 Nzmm- at 28 days. The results show that splitting of bamboo reinforcement into different shapes ???improves the interfacial bond because the newly exposed surface is rougher than the outer surface. Also, it is noted that arranging bamboo reinforcement splits with their concave facing upwards (HBU and QB) enhances bamboo reinforcement stiffness than those with their concave facing downwards (HBD) and whole bamboo culm (FB). This resulted to higher composite strength in HBU and QB reinforced concrete beams than those ofFB and HBD reinforced concrete beams. It is concluded that the use of splitted longitudinal aligned continuous bamboo in the reinforcement of concrete gives rise to significant improvement of the mechanical properties of concrete. The recommendation is made that bamboo pieces with an average width of 20mm and with their concave part facing upwards, could be used to reinforce concrete beams.

Stress strain relations for steel fibre reinforced concrete beams in shear

Author: Nyomboi, Timothy

Awarding University: Moi University, Kenya

Level : MPhil

Year: 2001

Holding Libraries: Moi University Margaret Thatcher Library ;

Subject Terms: Concrete ; Civil engineering ;

Abstract:

Fibre reinforced concrete is a relatively new construction material, with increasing application by the construction industry worldwide. Steel fibres have been found to offer significant increase in the shear strength of plain concrete. Recent research has shown that steel fibre reinforced concrete beams exhibit ultimate shear strengths of the same order as those obtained from conventionally reinforced beams (with stirrups) even at a fibre volume of 0.25%. This can be quite advantageous when used in structural members such as ring, lintel, and foundation beams because problems associated with fabrication and placement of conventional steel stirrups, labour and overall costs can be reduced. However, the limiting factor in the use of this material for the purpose discussed above is the lack of design guidelines that can be used in the design for shear in the structural members utilising the material. As a contribution to the development of design guidelines, evolution of the shear stress - strain behaviour in steel fibre reinforced concrete beams was investigated and linear limit and ultimate strengths were determined. Seventeen beams with varying shear span to depth ratio and steel fibre content were tested in three point bending while monitoring the load and the strains at selected points. The beams were reinforced in bending using steel bars with steel fibres as the shear reinforcements. Twelve cylinders with same fibre content as that of the beams were tested in compression while monitoring the load and strains (horizontal and vertical). Theoretical predictions of the non-linear behaviour based on a modification of hooke's model in which a strain dependent factor is introduced and a more advanced model based on the Imam et.al [23] were made and the two models could describe the experimental results satisfactorily. The prediction of the non-linear behaviour of the shear stress strain - strain was quite good from the two models particularly for the 0.5% steel fibre content. It was established that the linear limit is about 67% of the ultimate shear strength on average. The design application of the two proposed models with steel fibres as shear reinforcements and the classical design method of using shear links was made based on a practical design situation of ring/lintel beam. With the worst condition of loading on the design beam chosen, it was established that the shear stress that arise in lintel / ring are not so high to warrant the use of shear links and could be replaced by steel fibres with use of the proposed models for design.

Study on geotechnical engineering properties and behaviour of sand and clay soils.

Author: Gathuka, S Waweru

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : MSc

Year: 1998

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ;

Subject Terms: Soils ; Sand and gravel ; Clay ; Civil engineering ;

Abstract:

Some understanding of the physical and mechanical properties of any soil is of fundamental importance in resolving some of the numerous Geotechnical Engineering problems often encountered. This study is mainly concentrated on the laboratory methods applicable in gathering reliable data on these properties. The testing procedures for all the tests performed and their importance is explained in details in the thesis. The kind of laboratory data obtained and presented in the thesis can be used in the understanding of the basic characteristics and behaviour of the soils tested. These data can also be used in assessing the bearing capacity and settlement susceptibility of the soil, particularly during the design of foundation works. This research study mainly focuses on soils in their dry state and under fully saturated conditions. This particular study is confined to sand and clay soils, selected to represent some typical soils found in Japan and Kenya. These soils are the Toyoura standard sand and Fukakusa clay, from Japan; and the Mombasa sand and red coffee clay, from Kenya. From the experimental results a comparison is done of the data obtained and some of the observed principal characteristics are highlighted. Work on this study looked at the physical properties of the soils required for their classification, and the mechanical properties requisite for evaluating the strength parameters and settlement behaviour of the soils. The physical properties' tests included; specific gravity, void ratio, grain size analysis, Atterberg limits, and the permeability test. . The mechanical properties' tests included; unconfined compression, direct shear, triaxial compression, and consolidation test. Due to the problems realised in obtaining undisturbed samples a method was devised for preparing remoulded clay samples. The procedure adopted in the preparation of remoulded clay specimens are detailed in the thesis report including some of the difficulties encountered. Also included is some field technique adopted in sampling undisturbed samples of the red coffee clay. A comparison of the behaviour pattern of the two sands from the stress-strain relationship, indicate that the strength factor of the soil is a function of the particle size gradation. For the clays, the stress paths obtained point to the conclusion that the stress history of the soil influences the stress behaviour of both normally consolidated and over-consolidated soils. The work carried out in this study draws some analogies between sands and clays to show that models of the same type can be applied to both of them. This comparison does not change the traditional separation between cohesive and non-cohesive soils. The sands are realised to be more permeable with a drained behaviour (no cohesion), whilst the clays show undrained behaviour with an apparent cohesion Cu.

Parameter optimization of conceptual hydrological models (rainfall, runoff, catchment).

Author: Eeles, Charles William Owen

Awarding University: Open University, England

Level : PhD

Year: 1995

Holding Libraries: University Microfilms International ;

Subject Terms: Civil engineering ; Hydrology ; Mathematical models ;

Abstract:

The form of modelling used in this research for the simulation of the rainfall/runoff regime of catchment areas by mathematical models is of particular importance to civil engineers in the building of dams, river bridges and other works affected by high and low flows in rivers and streams. The parametric conceptual models can also be used in the management of water resources and as a basis for the assessment of long term risks associated with water storage and transmission of supplies. The objectives of this research are to examine the problems arising from the conceptual modelling of catchment areas with large data sets, and the effective determination of model parameters using gradient and non-gradient optimization techniques in the field of hydrology. A simple model package was developed from the application and modification of ideas current at the time which allowed a good fit to observed hydrographs to the achieved with the input of rainfall data and data for an evaporation loss function. Nine parameters were available for optimization in this model. The practical demand for the assessment of land use and its variations on catchment water yield led to the development of a more complex model with thirty-five parameters based on the latest vegetation process studies. One of the first modifications was to the criterion for convergence where it was changed from the rate of change of parameter values to that of the model coefficient of determination or efficiency of fit. The least squares objective function was investigated, and retained for model explained variance. However, for parameters involved in the simulation of base flows it was found to be more effective to use a proportional function, whilst for intense storm events an eighth power function exaggerated the information available in the data for determination of surface runoff parameters. The models employ an input data 'overlay' technique which allowed the use of large data sets running over many years. The simulation results from land use changes with large data sets from the highlands of Scotland, a clay catchment in Buckinghamshire and Montane rain forest in Kenya are compared and contrasted for both models. The results for these catchments using gradient and non- gradient optimization algorithms are also examined, including the use of a genetic algorithm, and recommendations made for the values of algorithm parameters. Hybridized algorithms are developed and tested. A combination of the rosenbrock and nelder and mead simplex techniques was found to be an efficient hybrid; particularly with the land use model.

Performance of crushed coconut shell as a course media filters.

Author: Ndiba, P K

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1993

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Civil engineering ; Filters ; Coconut ;

Abstract:

ABSTRACT NOT AVAILABLE

Mechanical properties of sisal fibre reinforced concrete.

Author: Mutua, Joackim Mukumbu

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1993

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ; University of Nairobi Upper Kabete Library ;

Subject Terms: Civil engineering ; Concrete ; Hemp ;

Abstract:

ABSTRACT NOT AVAILABLE

Optimization of floculation processes with respect to the physical parameters.

Author: Obote, Paito

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1992

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Civil engineering ; Water treatment ; Water ;

Abstract:

ABSTRACT NOT AVAILABLE

Laboratory and field swelling pressures of a black cotton soil.

Author: Goro, Evans C

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1988

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ; University of Nairobi Medical Library ;

Subject Terms: Soils ; Civil engineering ;

Abstract:

ABSTRACT NOT AVAILABLE