Doctor of Philosophy (Ph.D.)

Permanent URI for this collectionhttp://192.248.9.226/handle/123/12429

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item: Thesis-Abstract
Alternative building materials and methods for Sri Lanka
(2014-06-06) Jayasinghe, C; Perera, AADAJ
The housing requirement in Sri Lanka is rising due to the growth of population and urbanisation. This rising demand has to be met in an environment of rapidly rising prices of conventional building materials. Over exploitation of conventional building materials such as bricks, sand and timber has caused a number of environmental problems such as excessive clay and sand mining and deforestation. In this context, introduction of cost effective and environmentally friendly alternative building materials is of considerable importance. Such alternative building materials should be sufficiently strong and durable so that social acceptance would be at a reasonably high level. In the research work presented in this thesis, cement stabilized soil blocks are introduced as an alternative to brickwork and cement sand block work. These blocks are manufactured with laterite soils using a suitable machine. Since brickwork can be used as a load bearing material with considerable saving for residential buildings, an attempt was made to use cement stabilised soil blocks also as a load bearing material. This will require structural designing of residential buildings for which the design methodology, design data and the quality controlling required at construction need to be established. A detailed experimental programme was conducted to establish such information as apart of the research work presented. These findings can be used to carryout detailed structural design of cement stabilised soil block structures and hence it will now be possible for practising engineers to introduce this technology to Sri Lanka with a lot of confidence. A detailed design study and a cost study are also presented as guidance. Reinforced concrete solid slabs are often used in multi-storey residential buildings as the preferred option in Sri Lanka. These institute cast slabs need a considerable amount of form-work and false work. Since timber is a scare resource, the prices are increasing rapidly, thus making solid slabs an expensive solution for floor slabs. The utilization of concrete in solid slabs is also not optimum. As an alternative to institute cast solid slabs, a precast reinforced concrete composite beam slab system is introduced. Thsi system has optimized usage of concrete, steel and minimizes the need for form work and false work, thus leading to considerable savings in cost. The results of load testing are used to show that these composite slab systems can be designed by using the guidelines given in BS 8110: Part 1 : 1985. It is also shown that only 66.67% of the concentrated imposed load 4 need be considered for the design of individual precast slab panels of the composite system due to load sharing. A detailed cost study is also presented which can be used as guidance for cost comparison purposes. Therefore, now it would be possible to use this cost effective slab system in residential buildings with a lot of confidence and also to adopt it for other buildings as well.Key words: cement stabilized soil blocks, precast reinforced concrete slabs, alternative building materials.
item: Thesis-Full-text
Behaviour of in plane and out of plane curved steel beams strengthened with carbon fiber reinforced polymers
(2022) Weerasinghe KB; Gamage JCPH
Application of curved steel members in constructions have shown an increasing demand during last few decades not only due to the aesthetic appearance, but also some structural advances. The curved steel beams used in structures may be either curve on a vertical plane or curved in a horizontal plane. A considerable number of steel structures contained vertically curved steel tubular members such as in bridges and curved roofs. Horizontally curved steel members are mostly made with steel I beams which can be seen in bridges and floor beams. These curved steel beams (either tubular or I beams) need retrofitting due to many reasons; errors in design stage, loss of original material properties due to material degradation, exposure to severe environments, or load increments in service stage. Though many methods available to retrofit steel structures, CFRP becoming popular within industry due to many of its favourable properties; comparatively higher durability when considering with other materials, superior fatigue performances, higher strength-to-weight ratio, less labour requirement, and easy applicability for any sectional shape. This study focussed on the behaviour of CFRP strengthened vertically curved circular hollow sectioned beams and the behaviour of I beams curved in a horizontal plane strengthened with CFRP. The study was conducted in several stages as explained below. In phase one, Coupon tests were conducted in order to obtained the properties of steel tubes, steel I beams, CFRP and adhesives. All the specimens were prepared referring to ASTM standards and the tests were conducted according to same standard. Three samples from steel tubes, three samples from steel I beams, five samples from CFRP and Five samples from adhesive were prepared for testing. Tensile tests were conducted on all the samples and required properties for experimental studies and numerical studies were recorded. Some properties of the considered materials were calculated using empirical relationships found in the literature. In phase two, experimental and analytical study for vertically curved circular hollow sectioned beams were conducted. Total sixteen samples bent in to four radii 0 mm, 2000 mm, 4000 mm and 6000 mm were prepared. Three specimens from each set of beams were strengthened with 500 mm, 750 mm and 1000 mm long CFRP patches. All the beams were tested under flexure until the failure occurs. It was noted that the curvature of the beams and the CFRP wrapping length have showed a major effect on the maximum load carrying capacity of the strengthened beams compared to control iii beams. The proposed analytical method based on the equations found in literature to calculate the load deflection relationship of CFRP strengthened vertically curved steel hollow sectioned beams. The analytical model was verified using experimental results. In phase three, a numerical analysis was performed to identify the effect of sensitive bond parameters such as number of CFRP layers, elastic modulus of CFRP, aspect ratio of steel sections, CFRP layer orientation. 3D finite element models were created and validated compared experimental results prior to conduct the parametric study. With the parametric study results, it was found that the rise in number of CFRP layers increases the ultimate load and this ultimate strength gain does not proportional to number of CFRP layers (percentage increment in ultimate loads reduced with successive increase in number of CFRP layers). It was also noted that the increase in CFRPs elastic modulus drastically increase the ultimate load of CFRP strengthened vertically curved beams while CFRP wrapping configuration showed a significant effect too. It was also noted that there is no significant effect of aspect ratio of beams on the strength gain, however, for beams having same dimeter the ultimate strength gain reduced with the increased thickness. In fourth phase of the study, an experimental and analytical study was conducted on the CFRP strengthened horizontally curved steel I beams. The experimental study was conducted on twelve samples, consisted of beams bent in to three radii 0 mm, 4000 mm and 6000 mm. Three beams from each category was strengthened with three CFRP application profiles having 750 mm long CFRP patches while keeping one beam as a control beams. All the beams were tested under flexure until the failure with fixed end conditions at the either ends of the beams. The load-deflection responses and the failure modes were recorded. It was noted that the curvature of beams and CFRP application profile has significant effect on load-deflection behaviour and failure modes of CFRP strengthened horizontally curved steel I beams. An analytical model was developed base on the available literature to analyse the load deflection behaviour of CFRP strengthened horizontally curved steel I beams. The results obtained through experimental study and analytical method showed a good agreement which enable the use of analytical method for practical applications. On the final stage of this research, a numerical study was performed in order to evaluate the effect of various bond parameters on the ultimate strength gain of the iv CFRP strengthened horizontally curved steel I beams. 3D finite element models were developed using commercial available finite element modelling software and the results of numerical models were calibrated prior to conduct the parametric study. Influence of CFRP bond length, elastic modulus of CFRP, number of CFRP layers and elastic modulus of steel were studied. It was found that for both straight and horizontally curved beams strengthened with CFRP, ultimate strength increases until CFRP length increased to 750 mm. But, increase in CFRP length greater than 750 mm reduces the ultimate strength, and hence the optimum economical length of CFRP may be taken when CFRP length to span ratio become 0.75. Increase in elastic modulus of CFRP enhance the ultimate load for straight beams. However, this effect is not significant in beams curved to 4000 mm radius. The increase in CFRP layer count drastically increase the ultimate load for both straight and horizontally curved I beams. It was also noted that the percentage strength gain reduces with the increase in elastic modulus of steel.
item: Thesis-Abstract
Bus and rail travel modelling for Colombo metropolitan region : a theoretical approach to mode choice modelling
(12/2/2011) Widanapathiranage, SJ; Kumarage, KAS
The most common approach to modelling in Sri Lanka is based on zoning of the area concerned, and the identification of the travel network within the area, connecting the different zones. The resulting travel patterns of bus and rail are understood as an inter-zonal travel made between the different zones. The set of models used for transportation planning in the Colombo Metropolitan Region has inconsistent structural forms with the formulation of different types of variables. Most of these variables are not common to each other. As a consequence the model estimation requires a large data base. Pertaining to this, a set of bus and rail passenger demand model forms is calibrated to a common modelling format, on a scientific basis. These models attempt to explain (a) bus travel demand, (b) rail travel demand using season tickets,(c) rail travel demand using ordinary tickets and (d) total bus and rail travel demand. In these models, the impedance to travel is expressed in a generalized form, which includes travel fare, waiting time, transfer time and travel time. The product of employee population and the housing density between zones are the best fitted variables which explain the travel characteristics of the region. The Mode choice modelling is one of the most crucial parts of travel demand modelling. With regards to this, the sound theoretical approach to the modelling facilitates the better understanding of traveller behaviour in the mode choice process. The theoretical framework of the bus and rail choice model has been formulated using logit theory, energy theory and economic theory. The variables fitted in this model are expressed by time variables such as, the utility difference between passengers (a) walking time to the mode, (b) in-vehicle travel times of bus and rail and (c) the loss of traveller comfort due to the loading levels and waiting time of the modes. The inclusion of bus and rail loading factors in the model, is important and has a great ability to represent the traveller characteristics of the inter-zonal travel. Therefore, the model can be applied for transportation planning studies not only to the study area but also to any Metropolitan region in the developing countries, which is of a similar nature in the travel characteristics. The statistical tests reveal that the set of demand models for bus, rail and total public transportation has been successfully calibrated. It indicates the variation of the coefficient of correlation is between 70% and 80%. In fact, the choice model indicates this value is 85%, and 0.289 of the log likelihood index, which makes one conclude that the theoretical choice model has an acceptable fit, of the variables and the data.
item: Thesis-Abstract
Coconut fiber reinforced polymer composite for non-load bearing panel walls
(2022) Dharmaratne P D; Halwatura RU; Nilmini AHLR; Jayasinghe R
The study's main aim was to develop a lightweight walling panel for apartment buildings by employing coconut [coir] fiber with waste polyethylene. In this study, the flexural performance of coconut fiber reinforced polymer [CFRP] sandwich panels with different core configurations has studied experimentally and numerically. The numerical investigation was carried out using finite element analysis software “ANSYS 17.2”. The coconut fiber reinforced polymer sandwich panel was developed with thin CFRP sheets for the outer faces and cell arrangement for the internal core structure which was made by the same CFRP sheets. The sequences of cells with different core structures were considered to determine the optimum solution for flexural behavior. The first part of this study was the investigation of coconut fiber's physical, mechanical, and chemical properties by using an experimental investigation and a literature review. The next step was to develop the CFRP composites. In this study, the coir fiber was used as reinforced material, and the waste polyethylene was utilized as a matrix material. Composite was developed using hand-layup techniques by varying the coir length and coir weight fractions. This composite material was analyzed using ASTM standards for tensile and bending performance. The sample which optimum results obtained relevant to the coir length and weight fraction were used to develop a composite sandwich panel of 400mm x 400mm in size. The most suitable manufacturing conditions were also studied. The flexural properties of this panel were inspected using experimental and numerical methods. The three-point bending test was carried out to investigate the maximum failure stresses for the panel sample. The next part of this study is to develop the numerical models for the three-point bend test using finite element software. Then, the experimental results obtained from the three-point bend test and numerical outcomes are compared and validated. In the end, the numerical analysis is expanded to examine the sample panel's flexural performance of different cell arrangements. Finally, the failure stresses and the volume at minimum failure stress were identified for each cell configuration. This result concluded that the best cell configuration with minimum weight for wall panels was the result. The proposed wall panel should be durable and low-cost. Therefore, service characteristics and production costs were analyzed. Further, to extend this research, the proposed wall system's life cycle cost and embodied energy were analyzed to identify the long-term benefits of the proposed walling system.
item: Thesis-Abstract
Conjunctive use of surface and groundwater to improve food productivity in a restricted area
Sivakumar, SS; Senarath, DCH
This thesis presents alternate policy decisions based on technical strategies to operate minor and medium irrigation schemes with integrated conjunctive use of surface and groundwater to improve groundwater systems in a restricted area for the economic pumping for agricultural and domestic water use, by optimizing the use of groundwater and surface water. A groundwater simulation model was formulated using integrated finite difference method to carryout this research. Unlike finite difference method the integrated finite difference method can be formulated to any shape of catchment by connecting perpendicular bisectors of the observation points through out the catchment. An electronic spread sheet model was developed for groundwater system in integrated finite difference method and was applied to a selected restricted catchment area of about 185.23 km2in Vavuniya, for testing its validity after calibration. Forty one domestic dug wells were identified as observation wells among the available domestic/agro wells within the study area of 185.23 krrr', to represent the aquifer. This study area was divided into forty one Thiessen polygons by connecting the perpendicular bisectors of adjoining observation wells. A groundwater simulation model was formulated for this polygonal net work using integrated finite difference method in spreadsheet. The model was calibrated for the period 1997 to 2001 having eight seasons. The recharging period of eight months was taken as from 1st October to 31st May of the following year and discharging period of four months was taken as from 1st June to so" September. By this calibration the hydro geological stress parameters such as Transmissibility, Storage coefficient, Recharge coefficients for irrigation tank, irrigation field, rainfall and the Withdrawal factor for agro and domestic pumping were found using an optimization technique. A complete water balance study for each polygon for each season was carried out. Forty one error models have been prepared for the water balance, for each polygon for all the seasons. To avoid the negative and positive errors getting cancelled, the squares of all seasonal errors were added and minimized with suitable constraint. Practicable ranges for Transmissibility, Storage coefficient, Recharge coefficients and Withdrawal factor were given during minimization as constraint. MAT was used for this optimization. This model in spreadsheet, calibrated by error optimization technique, validated and recalibrated was used to predict the system behavior for various operational policies of the selected restricted groundwater catchment. Water levels were predicted for changes in operational policy of minor and medium irrigation schemes by forgoing certain percentage of cultivation, boundary treatment to reduce the transmissibility in steps, and combination of both. The economic feasibility was analyzed by taking the energy saved in pumping of raised groundwater as a benefit and boundary treatment cost and income loss due to change in operational policy of minor and medium irrigation schemes by forgoing certain percentage of cultivation as cost. The present worth of benefit and cost for various interest rate and project life period were calculated and compared. Change in operational policy of minor and medium irrigation schemes by forgoing one third of the cultivation under them or keeping one fourth of the storage of minor and medium irrigation schemes at any time together with 40% - 50% reduction in boundary permeability will recover an average of 60% to 70% of the loss of water table in any consecutive season in almost 95% of the area under consideration.
item: Thesis-Full-text
Decision-making model for energy efficient technologies in green buildings
(2023) Abeyrathna MPWP; Halwatura RU; Kaklauskas A; Perera AS; Arooz FR
Employee satisfaction is paramount as it directly impacts their productivity and health, particularly in the office environment, where thermal comfort plays a crucial role. Existing quantitative methods for evaluating thermal comfort satisfaction solely focus on building structural elements. To bridge this gap, a study was conducted, surveying 1091 staff members across 14 green office buildings to assess their satisfaction with indoor environmental quality (IEQ) comfort. The analysis introduced a proposed network of IEQ comfort features to aid in designing the questionnaire and measuring the environment. To address the issue of an imbalanced dataset, the study implemented various resampling methods along with feature selection techniques that integrated statistical analysis methods and machine learning algorithms. Developing predictive models using the Random Forest algorithm allowed for a comparison with Decision Tree, Lasso Regression and Support Vector Regression models. Three predictive models were created to assess thermal comfort, visual comfort and indoor air quality comfort separately, and one predictive model was created to assess the overall IEQ comfort. The study identified significant factors influencing IEQ comfort satisfaction, the share of the area served by AC, total window area, the thickness of the wall insulation, area served by lighting, and smart controlling. The predictive models achieved more than 75% accuracy, and interpretability supports their practical application in office design. By utilising this predictive model, building designers and managers can make informed decisions, uncovering situations where green building certifications may not meet employees' expected level of thermal comfort. Ultimately, optimising employee thermal comfort can lead to enhanced productivity.
item: Thesis-Abstract
Decoding the potentials of vernacular timber preservation technology for structural applications
(2022) Mendis MS; Halwatura RU; Somadewa R; Amarasekara H; Jayasinghe R
ABSTRACT Along with the celebrated history in the field of construction in the world, wood has been a building material for hundreds of years. The stability of timber structures is influenced by their reliance on external factors as it’s a hygroscopic material. Where the moisture content has an impact on almost every structural parameter, including strength, stiffness, and dimensional stability. It is also extremely vulnerable to biological degradation caused by insects, fungi, and bacteria affecting the molecular structure. These scarcities were undertaken in traditional wooden structures in a significant, yet sensitive manner in a tropical country like Sri Lanka. The durability of traditional wooden constructions exists under a highly appreciable status. In a tropical environment, the prolonged physical sustainability of wood is a challenging task. These show a greater degree of tolerance in the harsh tropical environment. Empirically expressive information sources were investigated, therefore structures for shelters were selected for further analysis. In this case, Tampita Vihara (the shrines on pillars), Devala (shrines dedicated to deities), Ambalam (resting places for travelers), and Mandapa (the assembly spaces for administrative practices) of which physical remains are still available in a relatively preserved state of standing evidence were carefully chosen. Numerous literature findings are documented on their religious beliefs and the significance of their architecture. But the structural engineering aspects relevant to material perspectives have not been studied adequately. A holistic investigation of timber in construction was carried out using knowledge from traditional vernacular buildings. Traditional vernacular v 1 construction relied on a thorough awareness of the surrounding environment, as well as the characteristics of locally available materials and manual labor. Traditional people are essential stakeholders in forest management because they are often economically, socially, and culturally reliant on forests. This resulted in building artisans attaining a profound knowledge of the utilization and manipulation of materials. This study examines the state of the structures, which entails a thorough understanding of past and present conditions. The goal of collecting extensive data from various typological structures is to establish a knowledge basis for the future. Field survey analysis around Sri Lanka was conducted to accumulate and consolidate the traditional vernacular timber processing and preservation technologies. Results disclosed wood logs burying under paddy field mud as a well-established technique to treat wood. As well, three dominant plant species were identified as Mikania micrantha, Titonia diversifolia, Gliricidia sepium assorted with paddy field mud to enhance the properties before treatment. Further, the field survey results and the microscopic investigations proved Mangifera indica wood was used for roof elements utilized after the above treatment in traditional vernacular structures with in the use life range 40 to 50 years. This showed its potential to be used for structural applications after proper treatment. Finally, an experimental trial was performed to evaluate the traditional vernacular technology with amendments, reinventing two types of wood preservatives based on the material matrix as plant extracts assorted with paddy field mud and only plant extracts obtained for water. This combination of traditional vernacular and contemporary aspects could offer an interesting and profitable approach to the further development of the wood industry. Keywords: Timber architectural typologies; timber preservation technology; Mikania; Gliricidia sepium; Titonia diversifolia; Plant extracts; wood preservatives. 1 The term vernacular comes from linguistics, where it refers to language usage specific to a time, region, or group.
item: Thesis-Full-text
Developing a roof slab insulation system for tropical climatic conditions
Nandapala, K; Halwatura, RU
Global Warming is proven to be one of the biggest issues that the current world is facing. Greenhouse gas emission due to the extensive energy usage has been identified as the primary cause for that. Hence, the world is on its path to investigate ways and means of reducing energy consumption in the world. On the other hand, due to the rapid urbanisation took place in recent history, land prices have escalated significantly. Hence, flat roof slabs become popular day-by-day due to the possibility of land recovery by that. Further, it has many additional advantages like cyclonic resistance, the possibility of future vertical extension and the possibility of utilising as an extra working space. However, a serious matter of concern is its thermal discomfort, for which air-conditioning the corresponding spaces is the most common remedy used. However, it has led to extensive use of energy, increasing the operational cost of the buildings and contributing to global warming, which is the issue that the world is attempting to mitigate. Hence, the current trend is to go for passive techniques. In this process, insulating roof slabs has been identified as a better passive way to make buildings thermally comfortable. In this study, several existing roof slab insulation systems and their performances were investigated, and the most efficient system for tropical climates was identified. Since that system had an issue in durability as it had poor drainage arrangement, an optimised system with a structural arrangement of discontinuous strips was found out by computer simulations. A physical model developed to verify the results showed that the newly developed system could withstand a point load of 4MT at its most critical locations. A comparison of thermal performance between the new system and the existing system was carried out by small-scale model testing. It resulted in finding that the newly designed system performs better than the most recent and efficient existing insulation system. An actual scale model testing was carried out to check its performance under real conditions. The results suggested that this newly developed system performs well in thermal aspects under actual conditions, and performs better than even a calicut tiled roof with a timber ceiling. Results suggested that this system can produce a peak cooling load reduction of about 20%. The performance of an air gap as an insulator was checked in the process of trying to replace the insulation material and found out that air gap is marginally less effective than polystyrene. Further, it was proven that the thickness of the air gap does not have a significant effect on the thermal performance. Further, a confined air gap with bamboo strips was also proven to have a similar thermal performance. An added vegetation layer on these systems further enhanced the thermal conditions of the building. A life cycle cost analysis suggested that the overlaid vegetation performs slightly better than the cases without vegetation in economic aspects. But the life cycle costing values lie in the same order, proving that all the systems considered are almost equally effective in terms of economic performance. However, due to the advantages like local and natural availability, bamboo, as an insulation material, is very favourable to be used in local context.
item: Thesis-Full-text
Development and validation of a novel CFRP/steel hybrid crack repairing technique for the steel structures
(2023) Abeygunasekara S; Gamage JCPH; Fawzia S
Steel structures such as steel bridges greatly contribute to the socio economic development of the world. The current traffic demand has exhausted the service life of steel bridges paving the way for failures without prior warning due to fatigue. In fact, fatigue contributes to change the microstructure of a material which fails below the yield point. Therefore, fatigue could be considered as an issue related to materials, even though it is linked to the area of engineering. Interestingly, several unavoidable stress types on structures occur on steel bridges due to various reasons. As a result, avoiding fatigue on structures has become impossible during their service life. The result of stress fluctuation has caused crack initiation on steel structures while the initial stage is at a micro scale level and not visible to the naked eye. Thus, it should be controlled at the initial stage avoiding adverse effects later. Although the conventional crack repair techniques have extended service lives of structures they have led to numerous drawbacks too. The crack stop hole technique could be considered as an emergency repairing technique to extend the fatigue life of a cracked steel structures that is quick, simple and economic. This technique was successfully applied in the aerospace industry primarily, however there had been irregularities due to the size of the hole with re-cracking appearing due to continuous service loads. Carbon fiber reinforce polymer (CFRP) materials have become popular as it has potential to replace the conventional repairing techniques with recent research focused on CFRP materials due to its light weight, corrosion resistivity, damping characteristics, fatigue resistivity and high tensile features. Therefore, this study proposes a crack stop hole (CSH) technique combined with a CFRP strengthening method to acquire the lost capacity due to fatigue in old structures with delaying re-cracking by further continue their services by steel bridges in the road and railway network operate at present. An experimental test program carried out to determine the behavior of strengthened and nonstrengthened CSH in steel members subjected to low cycle flexural fatigue. Overall, the test program was focused on estimating yield strength losses and yield strength gained by CFRP. Interestingly, various types of fatigue testing apparatus are available in the open market for a relatively high cost which is not affordable in a university laboratory, thus a hydro-electric controlling fatigue loading apparatus was designed and fabricated as an initiation to this research study to fulfill this vacuum. In this development process, machine operation, and development technique with finite element analysis on the test frame was investigated. In the next phase of this research, a numerical model was developed using an advanced finite element model (FEM) and results were validated using the laboratory test results. The proposed numerical model was based on the cyclic J-integral method under the detect cyclic mode. The test results agreed with the model results consisting nine key parameters affecting the final results. This CFRP strengthened CSH technique is significantly enhanced fatigue life of the structural members. This investigation reported the yield strength losses; which are in the range of 13.4 % to 25.2 % compared to the non-conditioned and yield strength gains with CFRP; which is in the range of 32.2 % to 45.3 % compared to the non-strengthened CSH with the diameter varies from 4 mm to 25 mm. A considerable amount of strain controlled were recorded by CFRP with respect to non-strengthened CSH. When considering the critical parameter effects, the test results recorded a yield strength gain with respect to off-set distance; which was in the range of 36 % to 131 % compared to the CSH at the midpoint. The yield strength variation recorded due to the length of CFRP layer was in the range of 89 % to 223 % compared to the least length considered. This investigation recommended by CFRP strengthened technique has significantly enhanced fatigue bearing capacity of structural members with CSH. Design guidelines are developed for practical implementations.
item: Thesis-Full-text
Development of a GIS based transport demand estimation model that integrates land use and transportation infrastructure development scenarios
De Silva, PCP; Bandara, JMSJ
Transportation issues are becoming severe day by day in Sri Lanka. Ignoring the importance of integrating transport and land use properly in the travel demand estimation process, due to its vast complexity and not having a proper mechanism to understand it easily, is the main reason for those issues. Identifying that, this research developed a GIS based transport and land use model that helps relevant authorities to easily understand and incorporate the complex interaction to the travel demand estimation process, as the first attempt in Sri Lanka until now. The model has two sub models called macro and micro models that separately look after the regional level and local level travel demand estimations respectively, although final results at any level combine both models’ outputs. The macro model has been developed for whole Sri Lanka taking the Divisional Secretariat (DS) divisions as Traffic Analyzing Zones (TAZs). Algorithms calibrated by the linear regression analyzing technique incorporating the Origin-Destination (OD) matrix data and socio-economic data are the main modeling technique for the macro model. Optimum counting locations derived through a new approach named as the “top-down approach” for OD surveys enhanced the accuracy of the OD matrix and thereby increasing the accuracy at all stages. As a prototype, a micro model was built for the Colombo DS division. The study area of the micro model can be any geographic area according to data and time availability. The activity based approach in the microsimulation modeling technique was used to develop the micro model, which uses household and railway passenger OD surveys, for calibration. Finally, a GIS based computer program was developed to improve the effectiveness and user-friendliness of these models.
item: Thesis-Full-text
Development of a guideline to coordinate traffic signals for a non-similar intersection cluster
Jayasooriya, NK; Bandara, JMSJ
Development of guidelines to coordinate traffic signals for non-similar intersection clusters Despite the mega scale projects focusing on the long term benefits, proper traffic management initiatives should be introduced and implemented to reduce the unnecessary delays on roads resulting in road user frustration. Traffic signal coordination has been identified as one of the most sustainable solutions, if properly utilized. When it comes to traffic signal coordination, various techniques are available for coordinating similar type intersections. However, when non-similar intersection clusters are encountered, no proper guidelines have been developed for coordination. The research sets out the preliminary requirements essential to be established for the progress of traffic signal coordination. As the first step, selection of an appropriate micro simulation model to support analysis and a procedure to identify and calibrate important input parameters are established. Second, guideline for signal phasing and timing design for individual intersections with fixed time signal timing is proposed. The guidelines are produced for intersections considering geometrical arrangements, traffic signal phasing and timing. Third, guidelines for real time traffic signal designs are produced where the guidelines address the extension of green split for different traffic situations. Finally, the criteria for selecting intersections that should be clustered for traffic signal coordination is established. When clustering, importance of relying on travel time than distance is discussed when developing clustering guidelines. Further, seven basic categories of non-similar intersections based on the intersection geometry and priority directions for green platoon are identified. Based on the analysis, two matrixes are developed for peak period and off-peak period to be utilized by traffic and transportation engineers when non-similar intersections are encountered for traffic signal coordination. The developed guidelines are successfully verified using two case studies, for a selected Baseline road intersection cluster for fixed time traffic signal coordination and Kadawata intersection cluster for real time traffic signal coordination.
item: Thesis-Abstract
Development of a hybrid air purification unit for the indoors in tropics
(2023) Weerasinghe, KGNH; Halwatura RU
Indoor air pollution poses a critical concern in today's world, influenced by various factors. Ensuring a safe indoor environment demands addressing the profound impact of pollution. Multiple strategies have been deployed to mitigate indoor air pollution, with a focal point emerging as biofiltration using indoor plants. This prompted a thorough exploration into the capacity of NASA-recommended indoor plants, which had undergone minimal experimentation in tropical climates. Simultaneously, an assessment was made on the efficacy of indigenous herb plants in curbing indoor air pollution. The plant selection process involved using a plant selection matrix to identify the most suitable plants for the study. Individual plant performances were rigorously tested within controlled chamber studies, evaluating their abilities to reduce carbon dioxide and other pollutant gases. The net performance of plant leaf area in carbon dioxide assimilation was measured and compared, resulting in a ranking of plants based on their performances. Among these categories, the Peace Lily (Spathiphyllum blandum) and Thippili (Piper longum) plants emerged as the top performers. Using these selected plants, a hybrid air purification unit was innovated, combining natural plant-based purification with modern technology and additional functionalities. Subsequently, the actual-scale performance of this developed system was assessed to determine its environmental sustainability. A comprehensive questionnaire was employed to gauge the social sustainability aspect. The plants' performances were also evaluated in air-conditioned settings, followed by an economic comparison to ascertain practical feasibility. The culmination of these endeavors has revealed that employing specific combinations of indoor plants facilitates achieving desired indoor air quality levels, particularly in terms of reducing carbon dioxide levels. This practice is beneficial economically and is highly recommended for indoor spaces where individuals spend approximately 90% of their time. Ensuring indoor safety becomes paramount, and this Hybrid Air Purification Unit not only contributes to energy savings and enhances environmental air quality but also encompasses the immeasurable aesthetic and therapeutic effects of plants. Keywords: Air Purification, Carbon Dioxide, Hydroponic Cultivation, Indoor Air Quality, Indoor Plants
item: Thesis-Full-text
Development of a sustainable energy rating system for residential buildings in Sri Lanka
Pathirana, SM; Halwathura, R; Rodrogo, A
Energy rating system can be considered as a key policy instrument that will assist the government to reduce energy consumption. Energy rating includes the direct bene ts such as, energy requirement and carbon dioxide emission reduction, cost reduction for the users, increase the public awareness regarding energy issues, and improve the availability of information regarding the building. The government of Sri Lanka also has identi ed the importance of energy performance of buildings and considers it as a strategy for the sustainable energy development of the country. Existing rating systems in the world only considered limited factors related to energy consumption and to provide more accurate rating system it is proposed that a more sustainable energy rating system should be developed considering all the criteria. This research is aimed at identifying the existing rating systems, investigate the existing systems, to identify the parameters required for determining the energy performance of residential buildings, to develop and equation for calculating the energy score and to develop a scale for comparing the energy performance of residential buildings in hot and humid climate in Sri Lanka. To achieve the above mentioned objectives, this research followed the concept of sustainable energy which comprises of both energy e ciency and renewable energy. The energy e ciency of a residential building needs to consider the energy e ciency due to building properties and energy e ciency of the occupants. To evaluate the energy e ciency of the building properties, the asset rating method was used where the building is modeled and the energy consumption for thermal comfort and lighting is calculated. Using 4569 di erent models (varying window to wall ratio, orientation, zone size, zone location, building shape and oor area), a parametric analysis was conducted to develop an optimum model which was then used as the reference value for the rst sub rating (Building consumption rate). A questionnaire survey was conducted to identify the factors a ecting the energy consumption of the Sri Lankan residential buildings and in total 336 lled questionnaires were used for parametric analysis. The questionnaire revealed that the number of bedrooms is not signi cant for energy consumption and the occupant characteristics and the equipment usage are highly signi cant factors. Therefore, when developing the occupancy behaviour rate, the average domestic energy consumption in Sri Lanka was used as reference, without normalising. To consider the renewable energy usage, another sub rating named energy source rate was developed and to decide whether to o set the energy consumption with renewable energy use or to use a separate index, another questionnaire survey was conducted with rooftop solar PV consumers. The results of the survey indicated ii that there is a strong rebound e ect due to the solar PV adoption and there are some other social and technical impacts as well. Therefore, when developing the energy source rate, a sustainability index was used and based on the percentage of contribution of the energy sources to the nal energy use the nal energy source rate was determined. These three sub ratings were normalised and brought to a common scale of 0 to 100. The sub ratings were integrated using weightages which were obtained using a perception survey of engineers, architects, quantity surveyors and facility managers in the industry. The application of the rating method is explained using two actual examples. Further, a sensitivity analysis was done to re ect the e ect of the changes in the parameters used in the score calculation equation using the rst sample house. The rating methodology proposed in this thesis can be used over any country or any building by changing the reference values and weightages. Keywords: Energy rating; energy e ciency; buildings; thermal comfort; renewable energy; energy labels; consumer behaviour
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Development of a theoretical packing model incorporating the effect of vibration, shape and surface texture
Hettiarachchi, HACK; Mampearachchi, WK
Determination of packing density of a particulate mixture is still an open problem for researchers and scientists. The complex and random nature of particle behavior in a mixture and effect of various external factors have made it more and more complicated to develop theoretical and analytical models to predict the packing density. This study focused on the effect of vibration frequency, particle shape and surface texture on packing density. Initially, laboratory experiments were carried out to determine the use of packing concepts in concrete mixture design for interlocking concrete block pavers (ICBP). The approach found to be successful. However, determination of packing density of aggregate mixtures in laboratory was time consuming and difficult. Hence, the use of packing models to determine the packing density was studied. Validity of existing packing models for the aggregate mixtures was studied and as a result the 3-parameter model was found to be the only model that incorporates loosening effect, wall effect and wedging effect and the percentage error of 3-parameter model found to be lesser than that of Toufar model and compressible packing model. Hence, the 3-parameter model was selected for the modification. The results obtained from experiments were then analyzed and relationships were developed isolating the effect of vibration, surface texture and particle shape. Three effects were combined, and the packing density variations were obtained to incorporate the effects and modify the 3-parameter model. The packing density and vibration shows a 3rd order polynomial behavior while shape and surface texture shows a linear relationship with packing density. The developed model was validated for more than 300 independent data. The behavior of loosening effect, wall effect and wedging effect with vibration, surface texture and shape were also analyzed. The wall effect is affected by both surface texture and vibration frequency. The loosening effect is affected only by particle shape and the wedging effect does not affect by any of these factors.
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Development of advanced design criteria for stronger lattice towers
(2021) Gunathilaka AMLN; Jayasinghe MTR; Lewangamage CS
The key lateral loads acting on a freestanding telecommunication/broadcasting tower are due to wind effects though occasionally seismic forces also can act. Though earthquake design guidelines are well covered directly or indirectly in many tower designs standards, telecommunication/broadcasting towers in Sri Lanka and in Indian subcontinent are not specifically designed for earthquake induced forces. Therefore, a detailed study was undertaken to determine the probable structural performances that can be expected from commonly adopted Four leg and Three leg self supporting lattice towers. For this study, the earthquake levels that can be possibly expected in Sri Lanka and in the South Asian region have been considered. A key parameter that can directly affect the seismic performance is subsoil conditions. Hence, a probable range of subsoil conditions have been considered in this study as certain subsoil conditions could amplify seismic waves under certain conditions. For a range of tower heights that are generally used, Response Spectrum analysis techniques have been used to assess the probable performance of lattice towers. An assessment was also made with equivalent static method to determine the applicability of it over a wide range of conditions. One of the key observations has been that the earthquake induced stresses on key members of lattice towers could be of lower magnitude than due to effects of wind. The parameters that could affect the seismic behaviour of a lattice tower are the subsoil stratum and the natural period of vibration of the lattice tower. The main finding of seismic analysis of lattice towers is that for the likely seismic hazard levels in Sri Lanka, key elements of towers will be subjected to much lower stress levels than induced by the winds of design magnitudes. However, if more severe earthquakes that could occur in the South Asian region are considered, there is a possibility for the earthquake induced forces to reach structurally significant levels. However, still such forces are less than the wind induced forces. For both earthquake and wind induced lateral loads, one of the key elements that needs careful attention is the connection of the tower to the foundation through baseplates. Baseplates are crucial elements related to structural stability of self supporting lattice towers. It acts as the interface between the tower body and the foundation. iii Due to structural characteristics of towers, uplift forces induced on baseplates govern the design of the baseplates. This is a rare case to occur on baseplate of buildings and other conventional structures. Hence, guidelines published in design codes and standard text books for design of baseplates are not really applicable for self-standing towers. This is a gray area that needs attention. Hence, an extensive study was carried out in this regard using Yield line theory to develop a design guideline. The developed theory was verified through a detailed experimental investigation and a finite element modeling using computer aided non liner modeling techniques. The formulae developed were modified for industrial applications considering all practical deviations which could not be addressed under fundamental theory using extensive parametric analyses carried out with the Finite Element models. The findings have been presented as design guidelines in the form of equations that can be used by structural design engineers undertaking free standing tower designs.
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Development of an optimized integrated rainwater harvesting model for multistorey houses
Sendanayake, S; Jayasinghe, MTR
Rain Water Harvesting (RWH) is an ancient civil practice of more than 4000 years, drawing attention among scientists in recent decades, in the light of potable water shortages and water based natural disasters such as draughts and flash floods. It is noted that much focus has been on optimizing the sizes and operation of individual components, in relation to increased Water Saving Efficiency (WSE), in order to minimize he overall capital investment. However, if RWH is to proliferate, it should function on par with centralized service water supply, particularly in delivering water to service points reliably. This is most relevant in urban, multi story scenarios, where not only service reliability but optimized utilization of space and aesthetic aspects is also important. Taking in to consideration that pumping of collected rain water is energy consuming and therefore against the principles of sustainability, a Cascading Multi Tank Rain Water Harvesting (CMTRWH) system is introduced for multi story situations, where the energy requirement on pumping is much less compared to the conventional models. Even though the CMTRWH model is energy efficient, unless an alternative, renewable power source is introduced to operate an efficient pump with total reliability, the system will have to depend on costly grid power, not only negating the positive impact of using RWH on sustainable development, but also depriving water security to vast communities of people without access to grid power. Sri Lanka being a tropical country, solar power option is pursued as the most desirable alternative energy source. Acknowledging the importance of a storage battery for the reliable operation of the power supply system, sizing curves are developed to select optimally matching pair of PV generator and battery for a given load, at a given location. In order to overcome the difficulty of obtaining measured incident solar radiation at remote locations, a methodology is developed to calculate solar radiation using easily obtainable rainfall data.
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Development of criteria for forming and maintaining a sludge blanket in an upflow sludge blanket clarifier/pulsator
(2019) Illangasinghe IMWK; Ratnayake N
Coagulation and flocculation is attained within a sludge (floc) blanket of an upward flow clarifier unit. In this study cohesivity of the floc blanket, measured by the indicator sludge cohesion coefficient (SCC) is used to explain the blanket characteristics and response of the blanket to variations of raw water turbidity (RWT), coagulant dose and ambient conditions. The study found that SCC is an appropriate parameter to monitor floc blanket characteristics. A satisfactory floc blanket is established when SCC varies within 0.3 – 1.3 mm/sec and the sludge volume fraction of the blanket is between 0.2 and 0.25. At RWT occurrences > 450 NTU, the blanket cohesivity reduces. Increased coagulant dose leads to restabilization of particles by charge reversal leading to reduction of blanket cohesivity. It is recommended to introduce preliminary sedimentation (prior to clarifier) to effectively treat high turbidity raw water. Beyond RWT 300 NTU optimum coagulant dose reported from SCC test is lower than that of Jar test. This will give savings in coagulants in the range of 6 - 25%. When RWT is > 300 NTU, the linear relationship established using the two parameters during the study can be used to find the optimum dose after carrying Jar test. The study found that high inflow temperature reduces blanket cohesivity and particle settling efficiency. There is a significant linear relationship between the influent temperature and the effluent quality. The particle structuring within the blanket is due to hydrodynamic forces between the particles counterbalanced by the cohesive forces. A steady floc blanket is formed when the individual particles are agglomerated and clusters are formed. Cluster formation/destruction is due to the cohesive/inertial forces between particles and/or particle clusters. With low Re (< 1) cohesive forces govern. Interstitial spaces between particles vary due to cluster formation/destruction, leading to the increase/decrease of blanket settling velocity.
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Development of disaster resistant built environments with commonly used building materials in Sri Lanka
Mallawaarachchi, RS; Jayasinghe, C; Jayasinghe, MTR
At present, sustainable building construction practices are actively promoted. One of the key strategies that can enhance the degree of sustainability is creating built environments that can last a very long time when very high level of disaster resistance is achieved with commonly available building materials in a very cost effective way. These strength enhancement methods should cover multitudes of disasters like cyclones, floods and earthquake tremors. Masonry is a very good material for carrying compressive stresses due to gravity loads consisting of self weight and live loads. However, alternative building materials such as Compressed Stabilized Earth (CSE) bricks and blocks and rammed earth can also demonstrate a behaviour comparable to conventional masonry such as burnt clay bricks and cement sand blocks. Lateral loads are the dominant of all forces acting in a disastrous situation. Therefore, flexural strengths of the building materials are of very importance. These lateral forces are static or dynamic in nature. In most instances, it may be possible to find equivalent quasi-static forces for dynamic forces. This means, an accurate assessment of the lateral load carrying capacity of masonry walls and also strategies available for improving the lateral load carrying capacities will be of importance. It is shown that for experimental determination of flexural strength parallel and perpendicular to bed joints, testing of panels with low degree of pre-compression can give reasonable results with acceptable level of scatter. This method has been used to determine the flexural strength parameters for both conventional and alternative materials. It is also shown that the presence of continuous tie beams at plinth level, window sill level and lintel level can create a situation where wall panels behave almost as vertically spanning. Since tie beams cap control the deflection in lateral direction while applying some pre-compression, it was possible to present a theoretical concept for determining the lateral load resistance with the enhancements possible with tie beams. This method relies on the compressive strength of masonry. Once this theoretical method is used with adequate partial factors of safety, a reasonable estimate of lateral load resistance can be obtained. This method can be used even with masonry having very low flexural tensile strength parallel to bed joints. The above method has to rely on the restraint offered by the continuous tie beam. This means that the tie beam should be adequately restrained. The ideal restraint can be the return walls that would generally occur at 3.0 - 4.0 m intervals in houses. It would also be advisable to have the tie beam extended at least 300 to 600 mm into the partition walls since it can provide better load transfer. This means that some of the plan layout may need some adjustments. Such an integrated approach could provide a house where the masonry walls are adequately tied at various levels and hence capable of transferring loads from one element to the other thus mobilizing various load resisting systems like that can be possible with shear walls. Even a well constructed house with these disaster resistant features can still suffer if the foundation fails. Thus, adequate soil improvements where sandy soil (s mixed with laterite soil and re-compacted in both foundation and also around the house would be essential. Three-dimensional finite element modelling with commercial software became a reality only recently. The use of such software like SAP 2000 to identify the likely behaviour under lateral loads was presented. A similar attempt was made to obtain the influence of the nearby houses under wind conditions using ANSYS software. With all these disaster resistant features, it would now be possible to create a robust single storey house with potential to last as long as possible. The same techniques can be adopted for multi-storey houses as well. Therefore it can be stated with confidence that the research presented in this thesis led to a development of an integrated approach for creating disaster resistant houses. Once such robust built environments are coupled with passive techniques already successfully used for adequate indoor thermal comfort, it would be possible to have robust houses that will need very low energy for day to day operations.
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Development of soil based flooring material for tropics
(2021) Galabada GH; Halwatura RU; Nilmini AHLR
The unplanned and rapid growth of developments has led to adverse impacts on the climate and biodiversity. Among them, the building industry is one of the foremost sectors. Therefore, the proper selection of building materials and techniques is of prime importance. Out of several sustainable materials, the soil has gained more attraction due to its advantageous features. Hence, this century has seen several notable milestones after passing thousands of years with the usage of soil in construction. Earthen flooring is one aesthetically attractive building element that has recently been restored and modernized. In fact, terrazzo, ceramic tiles woods, etc. are the widely available flooring materials associated with certain undesirable features. Hence, a necessity has arisen to seek alternative flooring materials. However, soil as a flooring material has not been investigated properly. Therefore, this research focuses on developing soil as a flooring material with sustainable features while pursuing possible means of increasing the strength of soil as a flooring material and enhancing the top surface finish. Then, the durability and service characteristics, cost benefits, thermal performance would be evaluated with the behavior on a real scale. The optimum soil gradation was first investigated. Next, investigation results showed that the increase in water content causes a decrease in the compressive strength, linearly at a constant rate for all cement percentages. The selected soil cement mix with water form a concrete and 150 mm standard cubes were used to determine the compressive strength. The best size and shape of test specimens were predicted and the relationship between compressive strength and specimen size and shape was identified in this background. Consequently, soil concrete was tested with the addition of metal as a course aggregate, but it did not influence the improvement of compressive strength in a significant level. Soil concrete with chemical admixtures showed that the admixtures were useful to enhance the workability and strength. The Mixed proportion consisted of fine particle contents 0-10%, a sand content 55%-60%, gravel content 30%-35% with a maximum gravel size of 25mm. The required cement was 18%-20% that depended on the usage of the admixture. The required moisture range was 16%-19% for soil concrete without admixtures to achieve a workable mix. To form the top surface to be architecturally attractive and for smoothness with regard to user comfort, the surfaces were smoothened in this background. Among several resins, one synthetic resin and floor sealer were selected and applied on the prepared soil floor samples as a surface coating. The Phenol-formaldehyde (novolac) resin was selected and cured with the Hexamethylenetetramine (HMTA) with heat treatment. The bonding capacity of coating in the soil floor, the water absorption, the abrasion resistance, the slip resistance and the stain resistance were analyzed according to the relevant standards to evaluate the soil floor with the resin coating for durability and service characteristics. Though all the tested parameters were within the standard requirements, the abrasion resistance of resin surface failed in this context. However, the floors which were with floor sealers showed positive results. At the end of the series of experiments, the mixing proportion, the top surface finishing material and the method of construction were decided for the continuation of the research. Thermal performance and cost benefits were then evaluated and compared with other selected existing floorings. According to the temperature variation pattern, the soil floor showed a significantly low top surface temperature compared to the other floorings and indoor air temperature. In fact, the Life Cycle Cost (LCC) for soil floor is significantly less compared to other existing floorings. Finally, the study findings suggest that soil could be used as a flooring material and a floor sealer could be used as a top surface finishing layer with a long-term sustainability. However, further research is required to find the suitability for a building's upper floors and the use of natural resin as a top surface finishing material.
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Development of wall putty for tropics using drinking water treatment plant waste alum sludge
(2022) Galkanda GAHH; Halwatura RU; Nilmini AHLR
Water is the main source of life; therefore, a sufficient amount of safe water consumption is essential for public health. It is one of the responsibilities of a country, to ensure the access of its citizens to consume sufficient safe water. In Sri Lanka, the national water supply and drainage board (NWSDB) is the responsible authority for drinking water purification and distribution. NWSDB owned 323 water supply schemes. In drinking water treatment plants, surface water is collected and treated to drinking quality removing impurities dissolved in surface water. In the purification process aluminium sulphate (Al 2 (SO 4 ) 3 ) (Alum) is used as the coagulant and generated alum sludge at the end. The sludge disposal to surface water bodies creates the undesirable formation of mud deposits according to the activation of alum. Direct discharge of sludge into water bodies creates damage to its’ creatures and ecosystems. Therefore, direct disposal of alum sludge in open lands and water bodies is prohibited by legislation. Dewatered alum sludge is disposed at landfills and rock blasting wells. However, the increasing daily generation of sludge is creating an urgent necessity for a sustainable solution. The increasing amount of daily alum sludge production has considerable environmental and economic concerns in most countries. Therefore, the world's attention turned to finding a sustainable way to reuse or recycle DWTP alum sludge. This research aimed to address the issues mentioned, by developing a wall putty using waste alum sludge generated in drinking water treatment plants (DWTP) in Sri Lanka. Properties of the DWTP waste sludge differ according to the climatic conditions, geographical conditions, water treatment process and raw water quality. The research was conducted after the identification of the properties of DWTP waste alum sludge of different plants. Laboratory experiments were conducted to study the properties of sludge samples collected from DWTPs in Ambathale, Biyagama and Kandana. Biyagama DWTP was selected to collect sludge for the study due to the low moisture content and high solid content compared to other samples. Waste sludge is discharged at the end of the water treatment process, in semisolid form with high moisture content and it is dewatered through a sludge treatment process in Biyagama DWTP. Dewatered sludge generation of the plant is estimated at 10m 3 per day. Properties of DWTP waste alum sludge were studied. According to the results, moisture content variation, volumetric shrinkage variation, chemical composition and heavy metal analysis of the sludge was analyzed. In the first phase of the study, experiments were conducted to develop a wall putty mix using wet alum sludge. Test results reveal that volumetric shrinkage can be reduced with physical additives and adhesiveness can be improved with binders, but a wall putty mix cannot be developed with wet sludge by mixing additives and a binder, due to the high moisture content, high shrinkage and alum activation. In the second phase of the study, experiments were conducted to develop a dry powder from wet sludge overcoming the alum activation. To that thermal alterations of DWTP waste alum sludge were studied. Colour and density variations of the burned sludge at different temperatures were studied. Sludge becomes harder when burned, due to the alum activation and none of the processes that exist in the world, to produce dry powder from DWTP alum sludge. Alum activation of the sludge can be overcome by burning sludge with a lubricant. According to the experiments, coconut oil is identified as an effective lubricant. The density of burned sludge with oil is lower than that of burned sludge without oil at each temperature. Finally, a process was developed to produce dry powder from DWTP alum sludge. In the final phase of the study putty properties of the developed dry powder were analyzed and optimized and the performances of the developed wall putty mix were analyzed compared to existing wall finishes. And the real scale performances of the putty were tested. Finally, it was concluded that the developed dry powder is applicable as a wall finisher successfully on both interior and exterior walls. And also new research areas were identified for further studies from this research.