Master of Science in Civil Engineering

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item: Thesis-Full-text
Application of CFRP composite for sustainable solution of corroded slab system due to low nominal cover case study on nerd slab system
(2023) Ganewattha CK; Gamage JCPH
Carbon Fiber Reinforced Polymer (CFRP) strengthening technique had been shown excellent performance in externally strengthening reinforced concrete (RC) elements due to their superior properties compared to the alternative strengthening techniques. A substantial number of studies have been done to study the behavior of externally bonded CFRP strengthened RC elements. However, as per the knowledge, while most studies have focused on the external strengthening of RC beams using CFRP, and very few studies have focused on strengthening the pre-stressed beams and slabs. Pre-stressed concrete is most popular building technique in construction buildings. Steel corrosion is recognized as the most serious and dominant mechanisms of deterioration for concrete structures. Subsequently, the capacity of the pre-tension elements decreases after exposure to corrosion. NERD center slab system faces such unacceptable losses in load carrying capacity, stiffness, and ductility due to severe corrosion in pre-stressed beams. This study focuses on how CFRP can go for a load increment after reaching its ultimate load carrying capacity. The test procedure was arranged in two stages. The first stage testing was used to show the performance/ behavior of composite slab specimen and pre-stressed beam, with the application of load. The second stage of testing was carried out to make comparison between the structural performance of retrofitted and strengthen specimens. Specimens were selected for retrofitting after application of loading in stage 1. The total of 12 specimens were exposed to the loading and behavior of each of the specimen were observed. Specimens were selected as slabs and eight number of them were composite slabs with or without shear links which have overall dimensions equal to 1800 * 600 mm and other four were pre-stressed beams with overall dimensions of 1800 mm in length. In this study, CFRP is proposed as the economical solution which does not touch the structural integrity of the structure. All the specimens were tested using universal loading machine. In stage 1, specimens were loaded up to its ultimate failure. In stage 2, all the tested specimens were retrofitted using CFRP. In total number of six specimens were used for retrofitting. Another six specimens were also strengthened using CFRP before loading. In each stage of loading several observations were done. Such as mode of failure, cracking width distribution, ultimate load, and each composite panel's corresponding deflection were also recorded. In stage 1, flexural and shear cracks propagated in the pre-stressed beam and the beam failed at the applied load of more than 50 kN. Stage 2 focused on the performance/ behavior of the retrofitted and strengthened specimen after application of CFRP. The results from stage 2 showed a considerable reduction (nearly 20%) in loading of retrofitted/ strengthened composite slabs compared to control specimens. Difference in failure pattern is caused for this discrepancy in load demand of second stage. The experimental results showed some satisfactory performance in regaining the lost strength of the composite specimens due to corrosion.
item: Thesis-Full-text
Analysis and initial design of civil engineering structures using structural optimization
(2023) Lowhikan SS; Mallikarachchi HMYC; Herath HMST
Structural optimization of solids aims to find the optimal designs of structures by minimizing a constrained objective function such as the material compliance within a given problem domain. This constrained optimization problem is subjected to a set of displacement and load boundary conditions which in turn will be minimized with respect to a structural parameter. Although various structural optimization techniques have a sound mathematical basis, the practical constructability of optimal designs poses a great challenge in the manufacturing stage. The recent development in additive manufacturing partially side-steps this problem predominantly in the domain of Mechanical Engineering. However, in Civil Engineering structures, there is a great possibility of utilizing these optimization tools, especially in precast constructions. Currently, there is only a limited number of unified frameworks which output ready to manufacture parametric Computer-Aided Design (CAD) of the optimal designs. From a generative design perspective, it is essential to have a single platform that outputs a structurally optimized CAD model because CAD models are an integral part of most industrial product development and manufacturing stages. This study focuses on developing a novel unified workflow handling topology, layout and size optimization in a single parametric platform (Rhino-Grasshopper) which outputs a ready-to-manufacture CAD model with the assessment of their structural integrity. In the proposed method, the first topology optimized pixel model is generated for any two-dimensional problem and converted into a one-pixel-wide chain model using skeletonization. From the obtained skeleton, a spatial frame structure is extracted, and then its member sizes and layout are optimized. Finally, the CAD model is generated using Constructive Solid Geometry (CSG) trees and its structural performance is assessed. In addition, industry-standard structural sections can be assigned to the CAD model to be analyzed and designed in accordance with standard codes of practice.
item: Thesis-Abstract
Structural behavior of doubly curved shell structure constructed with mud-concrete
(2022) Jayasinghe RR; Halwathura RU; Nanayakkara KLU; Arooz R
Embodied carbon emissions have been overlooked in the past few decades. As such, today, the building sector is responsible for 38% of all carbon emissions in the world greenhouse gas emissions. To overcome the climate crisis, sustainable construction practices, reducing reliance on carbon insensitive raw materials usage and net-zero carbon standards are being implemented across the globe. Building with earthen materials becomes a focal point in sustainable building design practices since its an environmentally friendly construction practice. Although there are several earth-based modern construction techniques for walling available in Sri Lanka (such as rammed earth, mud-concrete), no reliable technique is developed or adopted as a slab system. Most of the recent earthen constructions are either single-storied or use concrete as their slab system. Thus, the earthen slab system would be a huge step towards a structure entirely made of earthen materials. Here, it is attempted to identify the structural behavior of the doubly curved shell structure using Finite Element Analysis (FEA) and the possibility of constructing an earthen slab system using Mud-concrete. It was identified that nearly 50% of cost reduction can be expected when compared with the reinforced concrete slab systems. A 1m x1m prototype Mud-concrete slab was constructed to check the potential for modular construction practice with a square footprint. The masonry mould method was used as the formwork system by considering the ease of the construction. Shell thickness of 50mm is the primary structural component, while the non-structural filling of 50mm from apex was used with the Mud-concrete mixture used as a flat floor surface.
item: Thesis-Abstract
Development of suitable planting mechanism for the Elephant forages in Sri Lanka
(2022) Tharangi UD; Halwathura RU
The elephants are considered the largest terrestrial mammalian in the world, requiring a larger amount of plant material for survival. The degradation and shrinking of forest of the island resulted due to anthropological activities. The ultimate result of the depletion and loss of habitats and niches is the elephant migration to explore new habitats and food sources. Food plays an important role in the elephant movement and is considered to be one of the factors leading to Human-Elephant Conflict (HEC). The within-range enhancements of the elephant forage availability led to within-range confine the elephant and reducing the gravity of the HEC. A study was conducted aiming to increase elephant forage availability in inaccessible rangeland by establishing elephant forage plants. The study proposed a mechanism for establishing forage plants through a device made up of bamboo cells. Information on the elephant forage plants was gathered through the field and literature survey. The information was placed in a database and used to prepare a Plant matrix. A questionnaire survey was conducted on the palatability of the elephant forage plants, and based on the responses, an index, the Forage Selection Index was developed. Bamboo was chosen as a construction material since the Biological, mechanical and physical properties of the material are well suited for the purpose. A device was designed from bamboo cells with varying diameters and cutting angles and optimum penetration depths. The optimized device was subjected to a field trial with eight elephant forage plants. The best geometric shape, diameter, and the cutting angle for the device for the optimum substrate penetration depth were shaped with double cutting, 7.5 cm and 45º, respectively. The grasses Pennisetum purpureum (Ali maana), Sacciolepis interrupta (Beru), Panicum maximum (Gini thana), and Echinochloa glabrescens (Bajiri) demonstrated better performance in the proposed device for the purpose of establishing elephant forage plants in inaccessible elephant rangelands. Further, studies are needed to improve the device performance for free falls from higher elevations and an array of elephant forage plants to generalize the findings.
item: Thesis-Abstract
Measuring full-field deformation of hyperelastic material using digital image correlation
(2021) Nadarajah S; Mallikarachchi HMYC
Digital image correlation, an optics-based strain measuring technique, has gained popularity during the last decade. The practice of employing digital image correlation-based measuring techniques in experiments has progressed dramatically owing to many incorporated sophistications: ease of use, greater precision, extensive measurement range, and stability of the results. While cutting-edge DIC measurement systems are commercially available, their high capital costs make them unaffordable for widespread usage. Several studies on establishing DIC-based measurement techniques with experimental validation have been undertaken over the years. The majority of prior DIC research concentrated on the testing of concrete, masonry, and metal alloy specimens, and little effort was made in assessing materials with substantial elongations. This dissertation presents an innovative DIC-based measuring tool for capturing surface deformation information with better precision. The proposed system is composed of two commonly accessible digital cameras as well as MATLAB-based algorithms. Uniaxial tensile tests of latex specimens are used to demonstrate the aptness of the proposed approach in capturing substantial deformations, and displacement estimates are validated against Vernier Caliper readings. A secondary high-precision measuring tool, the Ncorr program, was used to validate the integrity of the results produced by this technique. According to the comparison of results, it is proven that the system is capable of producing precise full-field displacement and strain maps with an apparent accuracy greater than 96 %. Furthermore, the similarity of the contour plots obtained using the proposed approach and outcomes of the Ncorr program verified the reliability of the proposed technique.
item: Thesis-Abstract
Investigation on carbon fibre reinforced polymer (CFRP) strengthened, out of plane curved concrete beam subjected to combined effects of shear and torsion
(2021) Fernando WCV; Gamage JCPH
Carbon Fibre Reinforced Polymer (CFRP) strengthening technique had been shown excellent performance in externally strengthening Reinforced Concrete (RC) elements due to their superior properties compared to the alternatives. A substantial amount of studies had been done to study the behaviour of externally CFRP strengthened RC elements. However, as per the authors’ knowledge, while most of the studies have been focused on the external strengthening of straight RC beams using CFRP, none of the studies had been focused on strengthening horizontally curved RC beams. Curved beams innately respond with flexure, shear and especially torsion under outof-plane loads due to its curvature. Hence, it is important to study the effect of the additional torsional stress on the CFRP external reinforcement. A detailed experimental program, a theoretical analysis and a numerical analysis were conducted in order to reduce the aforementioned research gap. A series of testing was conducted on beam specimens with 2 m and 4 m radii and externally strengthened with normal modulus CFRP fabrics to enhance the effects; shear, torsion and their combination. From series one experimental results, it was found that the wrapping CFRP fabrics have enhanced the shear capacity of the curved RC beams by at least 30 % and the enhancement is higher for beams with lower curvatures. It showed that CFRP wrapping is a very effective method to enhance the shear capacity of horizontally curved beams. The series two experimental results showed that U-socketing of CFRP fabrics for shear has increased the shear strength by 15.61 kN (16.7 %) and 17.41 kN (18.2 %) respectively for 2 m and 4 m radius specimens. The main failure mode was crack induced intermediate debonding of CFRP U-sockets. However, the predicted shear enhancements according to theoretical investigation are 23.64 kN and 24.51 kN for 2 m and 4 m radius beams respectively. It can be observed that for 2 m and 4 m specimens recorded respectively 33.97 % and 28.97 % less than the predicted enhancement by the theoretical study. This can be explained by the additional torsional stresses contributing to the direct shear stresses which cause to reduce the shear capacities of RC beams. The results from numerical models showed excellent agreement with experimental results which was used to carry out a parametric study. Subsequently, a capacity reduction factor was defined as the ratio between numerical shear gain and theoretically predicted shear gain to quantify the effect of torsional stresses on the shear enhancement of U-socketed CFRP on RC beams with a 1.4 m support distance which can be used to modify the currently existing analytical model adopted by ACI 440.2R-17 guide to design of FRP as external reinforcement for RC beams.
item: Thesis-Abstract
Methodology to develop a feeder bus network for a light rail transit system : a case study for fort- Malabe line
(2021) Mendis BHA; De Silva GLDI
The world is reaching towards the sustainable transportation and the public transport sector especially requires a better focus and attention. Public transport network can be better distinguished as mass transit systems and feeder systems. Mass transit systems strengthens the transport network as backbone transport systems. However, it does not enable the connection between the origins such as the residence or the work place and the mass transit access points. This connection which is a vital component is enabled by the feeder modes. There can be several variations in feeder modes. Especially it can be recognized as private feeders and public feeders. Without a proper feeder network, the maximum potential of a mass transit network may not be achieved. In this research, the focus is on the Light-Railway transit which is the most recent mass transit system that is being introduced to Sri Lanka. As the first step of introducing the light railway system to Sri Lanka, Fort-Malabe LRT was planned to be implemented. Even though the plans by the Government have changed, in this research, Fort- Malabe LRT line is taken as the case study in order to carry out the objectives. The feeder modes that are supplying to the LRT line were recognized as private vehicle drop offs, paratransit modes and short length public transit modes. In order to get an uninterrupted connection between the origin and the mass transit access station, the development of feeder network that will be serving the mass transit has to be parallel with the development of the mass transit system. However, the LRT orientated development also has to be limited by the necessity. In order to get a realistic estimation on the development required area, the spatial extent of access areas by different access modes have to be identified. The spatial area where potential transit users will origin their trip to use the mass transit can be identified as the catchment area. Catchments for different feeder modes may vary depending on the distance that users prefer to travel by that particular feeder mode. Catchment areas for multiple access modes were recognized using the survey data which were available from a previously carried out survey. In identifying catchment distances for different feeders, two methods were followed. First method was to consider each station and identify the preferred travel distances by a certain feeder mode to reach that station and thereby calculating a weighted average catchment distance for the chosen station for that particular mode. To calculate a catchment distance value which justifiably represents all the stations for a certain feeder mode, an average value was calculated. Second method that was carried out was to consider the LRT route aligned corridor and identify catchment distances for each feeder mode which will represent the Fort- Malabe corridor rather than each station. The individuality of stations was not considered. To identify the catchment distance for a specific feeder mode, all data records of trips originating from a catchment to reach any station by that mode were taken in to account. The frequency of access distances occurring was the basis of the second method. Therefore, the frequency of a certain access distances occurring was identified and thereby the cumulative frequency of access distances was taken. When the accumulation of frequency reached 85 th percent, the catchment distance at the point was taken as the catchment distance for that certain feeder. In order to determine the geographical buffer area, two approaches were identified that can be utilized. First was the circular buffer approach which takes the Euclidean catchment distance from the LRT station locations. Aspects such as the geographical barriers and the non-availability of road network were not considered in this case. The other approach was to take the service area. In this approach the travel distance of the catchment is determined via the road network. Considering the pros and cons of two approaches and the accuracy of the results by each approach, service area approach was appointed to be used. Thereby the catchment areas were configured for the access modes. The catchment areas for each feeder type were visualized with the use of Geographical Information Systems (GIS). In the case of the bus feeders, it was observed that the catchment area also depends on the bus route path layout. Areas which are parts of the bus catchment but does not get supplied with the bus network, can be identified separately. In this scenario, Conveyal analysis was used to identify the bus catchment which is limited by the availability of bus routes in the catchment which is bounded by the catchment distance. As per the first objective of the research, catchment area for multiple feeder modes were identified as above.
item: Thesis-Abstract
Coiling and deployment mechanics of tape-springs
(2021) Haggalla HHND; Mallikarachchi HMYC
Recent advances in space exploration call for smaller space structures that can be reconfigured to achieve large surfaces when in operation. Compact, lightweight structures that can be folded or coiled up for launch have been made possible thanks to self-deployable booms. These can then be self-deployed in orbit to support a variety of small spacecraft systems. However, prior understanding of deployment behaviour is important before launch. This study focuses on model reduction techniques in predicting the deployment behaviour of coiled long-narrow thin shells known as tape springs. Coiling, stowage, and deployment stages that demonstrate considerable crosssection deformation of the tape-spring are discussed. The developed numerical benchmarking model well agrees with the theoretical framework that has previously been established in terms of deployment time and stored strain energy. This numerical model has further been used in a stage-wise development of a beam-shell hybrid model. The effect of varying hub radius is introduced to the existing theoretical framework to predict the coiling and deployment behaviour more accurately.
item: Thesis-Abstract
Structural testing and characterization of Sri Lankan yellow bamboo Bambusa vulgaris
(2021) Vipushnan R; Jayasinghe MTR; Damruwan HGH; Platt S
Bamboo is a woody grass belonging to the sub family Bambusoideae of the family Poaceae (Gramineae). The increasing need for sustainable building construction and the use of natural local materials have made bamboo a popular material. Sri Lanka is an island nation located south of the Indian peninsula. It is a tropical country with distinct dry and wet seasons. Sri Lanka has nearly 5000 ha of natural bamboo forests and another 5000 ha of domestically cultivated land, scattered mainly in the South Western zone which amounts to 0.5% of the total forest cover in Sri Lanka. However, with the restoration of cascading reservoir systems in the Eastern Province, there is potential to have many marginal lands converted to bamboo plantations hence allowing for the growth and harvesting of bamboo in a sustainable manner for use in construction as a structural material. Sri Lanka is home to ten endemic species of bamboo. In addition, several exotic species have been introduced to the country. The bamboo plant has a variety of uses. Industrial utilization of bamboo can be through primary or secondary value addition, which enhances the market value of bamboo. Bamboo in construction is found in either full-culm or engineered form. Bamboo is limited in its application through its durability and its tendency to split. Hence it needs to be processed and treated to ensure its long-term usage. Bamboo structures should be detailed appropriately for the full protection of treated bamboo. Bamboo used for construction has to undergo harvesting, grading, cleaning, preservative treatment, and storage. Determination of structural parameters of Sri Lankan bamboo could be based on ISO standards since other standards are often based on ISO standards themselves and are more suitable for bamboo species from those particular countries of those respective standards. To date, the mechanical characterization of Sri Lankan bamboo species has not been found in literature. The widespread availability of Bambusa Vulgaris (Sri Lankan Yellow bamboo) led to it being chosen for investigation in this study. All bamboo culm sections in this study were obtained from a single supplier with initial moisture content and dimensions obtained on delivery. Once culm data was measured for all culms, a random selection of culms underwent preservation treatment prior to testing. The mechanical characterization tests provided a set of structural parameters including; average strength values in compression, shear, flat ring flexure and tension for Bambusa Vulgaris (Sri Lankan Yellow bamboo). All Strength values tend to show gradual increase from bottom towards the top of the culm. Comparison of treated vs. untreated strength values across all four tests showed no significant increase in strength initially due to preservation treatment. Average densities of test samples tend to show a strong relationship with their respective strengths, whereas average diameter does not. Comparison of average strength values of Bambusa Vulgaris (Sri Lankan Yellow bamboo) with the same species from Kenya as well as relatable other species from Thailand revealed that the average strength values of Bambusa Vulgaris (Sri Lankan Yellow bamboo) to be lower compared to the respective average strength values of other species except in the case of tensile strength. Sri Lankan Bambusa Vulgaris showed characteristic strengths of 17.0N/mm 2 , 2.0N/mm 2 , 16.0N/mm 2 and 20.0N/mm for compressive strength, shear strength, bending strength in flat ring flexure and tensile strength respectively.
item: Thesis-Full-text
Influence of matric suction on pullout resistance of soil nails
Rajeevkaran, P; Kulathilake, SAS
Soil nailing is a widely used slope stabilisation technique using the passive intrusions-soil nails. Soil nail is a reinforcement bar encased within a grouted borehole without any pre-tensioning. When the soil mass attempts to move down, a tensile forces mobilized in the intercepted nails will enhance the shear resistance by increasing the normal stress along the potential failure surface while reducing the shear stress to be mobilized for equilibrium. This enhances the factor of safety. The tensile force developed on reinforced bar depends on tensile capacity of the bar and pull-out resistance at the soil-grout interface. The contribution of matric suction in pull-out capacity of soil nails is often neglected in conventional design formulae to make it conservative. But most of the soil nails are installed in unsaturated region of soil and significant matric suctions would prevail. This paper investigates the influence of matric suction on pull-out resistance of soil nails. To ensure uniform conditions the nails were installed in a soil mass compacted under controlled laboratory condition in a test box with dimensions of 1.30 m × 1.08 m × 0.90 m. In this study, four soil nails were installed at an inclination of 50 to the horizontal. The pull-out capacity of soil nails measured under different matric suctions and overburden pressures were compared with the values estimated using the design formulae. The matric suctions varied by controlled wetting were monitored by tensiometers. A good agreement is found between the estimated and measured pull-out capacities and the influence of matric suction on the pull-out resistance was found to be very significant. The numerical analysis performed with Plaxis 2D justified the results obtained.
item: Thesis-Full-text
Disaster management frameworks in Sri Lanka and compliance with global standards
Jayasiri, GP; Hettiarachchi, SSL; Siriwardana, CSA
In the recent past Sri Lanka has experienced several significant natural disasters. At present, the DMC and all the line agencies focus on disaster management functions under the ministry of disaster management. The comprehensive disaster management program was prepared in 2014 and it is to be used up until 2018. Furthermore, it was proposed to identify mechanisms to integrate the Sendai Framework into the Sri Lankan national disaster management framework. However, during recent disasters, the DMC and the disaster management framework was under severe criticism from the public as well as the technical community. Therefore, the aim of this study is to investigate disaster management framework in Sri Lanka and its compliance with global standards. Initially an in-depth literature review was carried out to identify the terminology and existing local and international frameworks related to Disaster Management. Then the local frameworks were evaluated against seven criteria, which were identified after carefully analysing the requirements of the Sendai Framework. During this investigations several recent disaster incidents were referred as well. In addition, a case study was carried out to identify the status of some of the key components of coastal community resilience. Interviewing key professionals in the field of Disaster Risk Reduction in Sri Lanka and the focused group and panel discussions provided sufficient data for the analysis. Sri Lanka is in the process of aligning themselves with the Sendai Framework and Even though country lacks proper and efficient resilience mechanisms focused on the coastal communities, national efforts are underway to build up the coastal resilience. Training and public awareness campaigns, efficient funds, properly maintained hierarchy and concern to the coastal ecosystems are some of the enablers associated in building coastal resilience. Developing a multi-hazard map, improving the interagency cooperation, Use of social media to disseminate Early Warnings and focusing more on the development of a people-centered Multi-Hazard Early Warning Systems (MHEWS) are some of the recommendations given.
item: Thesis-Full-text
Study of deep beams using finite element approach
Jasotharan, S; Weerasekera, IRA
Beams are common structural elements in most structures and generally they are analysed using classical beam theories to evaluate the stress and strain characteristics of the beam. But in the case of deep beams, higher order shear deformation beam theories predicts more accurate results than classical beam theories due its more realistic assumption regarding the shear characteristics of the beam. In this study a hyperbolic shear deformation theory for thick isotropic beams is developed where the displacements are defined using a meaningful function which is more physical and directly comparable with other higher order theories. Governing variationally consistent equilibrium equations and boundary conditions are derived in terms of the stress resultants and displacements using the principle of virtual work. This theory satisfies shear stress free boundary condition at top and bottom of the beam and doesn’t need shear correction factor. .A displacement based finite element model of this theory is formulated using the variational principle. Displacements are approximated using the homogeneous solutions of the governing differential equations that describe the deformations of the cross-section according to the high order theory, which includes cubic variation of the axial displacements over the cross-section of the beam. Also, this model gives the exact stiffness coefficients for the high order isotropic beam element. The model has six degrees of freedom at the two ends, one transverse displacement and two rotations, and the end forces are a shear force and two components of end moments. Several numerical examples are discussed to validate the proposed shear deformation beam theory and finite element model of the beam theory. Results obtained for displacements using the present beam theory and the finite element model are compared with results obtained using other beam theories, 2D elastic theory and 2D and 3D finite element models. Solutions obtained using the proposed beam theory and finite element model are in close agreement with the solutions obtained using 2D elastic theory and 2D and 3D finite element models of ‘ABAQUS’.
item: Thesis-Full-text
Embodied analysis of a precast building system
Dissanayake, DMKW; Jayasinghe, C; Jayasinghe, MTR
Buildings are evolving throughout the history of mankind. When a new building system is introduced, the usual evaluation method is the monetary value. The adaptability to the climate conditions, structural capabilities and constructability are some other criteria for the evaluation. The building industry is consuming a vast amount of natural resources and also been responsible for a significant energy usage. With the recent developments in the environmental concerns all over the world, there is an increased the attention for the building sector. Due to the above reason new buildings have to be more environmental friendly than more conventional building systems. A novel walling system has been considered in this study, which consist of lightweight foam concrete panels manufactured with recycled expanded polystyrene (EPS) up to 50% of the total volume. Even though those panels have lot of advantages over the conventional construction methods, they need to be compared with the other conventional methods for the environmental aspects. Embodied energy analysis is such an established method to quantitatively analyse the environmental impact caused by a product. Therefore, detailed study was carried out to determine the embodied energy of those foam concrete panels. A comparative study carried out using a typical single storey and for a two-storey house and different building materials. Final results done for the case studies, indicated that houses constructed with cement sand blocks has the least amount of embodied energy and embodied carbon. However, houses constructed with EPS based lightweight foam concrete precast panels, can be a good competitor in terms of embodied energy and embodied carbon analysis, since it yields results much closer to the cement sand blocks. Reduced sand usage of EPS panelled walls is also an added advantage. Hence, it has the potential to be promoted as a mainstream walling material.
item: Thesis-Full-text
Development of fast and bouncy cricket pitches in Sri Lanka
Perera, WSU; Nawagamuwa, UP
Development of Fast and Bouncy cricket pitches in Sri Lanka Most cricket batsmen in Indian subcontinent face a great difficulty in batting against fast bowlers on English and Australian fast and bouncy cricket pitches. The lack of having such practice pitches in home is the main reason for their lack of performances in fast pitches. It had been discovered that the pace and bounce of a cricket pitch is governed by clay content, clay mineralogy, sand content, organic matter content and grass content of the top layer of a cricket pitch. Six local soils and one soil from India were tested for their index properties as the preliminary step. The soils which were fiilfilling the requirement of the soil properties of fast and bouncy cricket pitch material were selected along with the currently used soil for Sri Lankan cricket pitch preparation and used for the laboratory model studies. Six cubic samples for the frictic and bounce comparison were prepared inside the laborati y from selected three soils varying the swface grass content. The co-efficient of friction (\i value) and the co-efficient of restitution (e value) were determined by the bounce test and friction test respectively. Soils which had low value and high "e" value were selected as suitable soils for the further proceedings of the research. MU and TY along with MT (Mixture of both MU and TY) were selected to carry on further studies in an actual cricket pitches in order to check their ability to generate pace and bounce. Besides selected area of the cricket pitch was daily photographed and surface crack density was analysed using MATLAB software. MU was selected as the most suitable soil from among all tests soils and recommended to be used for the development of local fast and bouncy cricket pitches in Sri Lanka.
item: Thesis-Abstract
Effect of end anchorage on CFRP strengthened concrete beams
Wijerathna, DMN; Gamage, JCPH
Reinforced concrete structures are often being subjected to modifications and improvements during their service life. The main causes for improvements are design errors, changes in use, degradation due to corrosion of reinforcing steel, damage due to seismic loads, vehicular impact and excessive wear and excessive loading. Precautions for these issues are mainly in two types; repair and strengthening. Restoring the structures which became structural malfunction is known as repair. Improvements done in structures in order to achieve higher service loads or longer service lives are known as strengthening. As far as strengthening techniques are concerned, concrete jacketing, steel jacketing, precast concrete jacketing, prestressed concrete jacketing and external application of Fibre reinforced polymer (FRP) composite materials are the available upgrading methods. Structural strengthening with fibre reinforced polymers is a popular strengthening technique worldwide, due to its extensive advantages. The important properties of FRP’s are high strength, light weight, good rigidity, corrosion resistance, high elastic modulus etc. FRP’s are used to improve structures by means of increasing flexural capacity, enhancing shear capacity and confining concrete columns to improve axial compression load carrying capacity. When flexural strengthening with FRP is concerned, research studies show that a significant strength increment can be achieved with use of CFRP sheets as an external reinforcement. It also improves serviceability of structures. Failure of a CFRP strengthened beam for flexure can be due to flexure, shear, concrete crushing or debonding. The failure modes can be categorized in to two main types; classical failure and premature failure. Failure of an element due to yielding of steel bars, tensile failure of FRP sheets and crushing of concrete in compression zone are known as classical failure. Failure of element in any other method such as debonding of FRP, peeling off of FRP and concrete cover separation are premature failure modes. End debonding is the most common failure mode which has been experienced in practice. This mode of failure, limits the capacity by 60% to 80% of ultimate capacity (Mostofinejad 2014, Xiong 2007) of the system and induce sudden failure without prior warning. Different methods have been proposed in literature to delay end debonding. They are Mechanical fasteners, FRP pin and pan shape anchors, Near Surface Mount reinforcement, End wraps and use of wire mesh–epoxy composite. Among these techniques, end wraps are more beneficial since it contribute to shear capacity of the beam and help to improve ductility apart from preventing debonding failure. Although these techniques are advantages, they are not popular in the industry due to lack of technical data to quantify the effects. Previous research studies emphasise the need of proper design method to predict the strength enhancement gained due to end wraps. There are few studies ( Sawada et al,2003 Hawileh et al. 2013) carried out to investigate the interaction between resistance to debonding and the strength gain. Moreover, studies conducted in tropical countries are even less. This has lead to less confidence of using this technique by practicing engineers. Although there are several design guides available on design of externally bonded FRP systems, none of these guides address the effect of end anchorage on flexural strength gain. This study investigates the effect of end anchors on enhancing flexural capacity of reinforced concrete members, flexural strengthened with CFRP sheets. An extensive experimental program was carried out using reinforced concrete beams to understand the failure behaviour, stress distribution, deflection behaviour and flexural strength enhancement. It was observed that 98.53% strength increment could achieved by thespecimens flexural strengthened with CFRP external reinforcement over control specimens. When the flexural strengthened beams were anchored at the ends, the strength enhancement was 145% compared with that of unstrengthened beams. It was also observed that strain levels at the ends of longitudinal CFRP strips reduces significantly, when end wrap anchorage is provided. End debonding can be fully prevented by providing sufficient amount of end anchorage. The failure mode of beams changed from cover debonding to CFRP rupture, in existence of end wraps. A new theoretical model was developed based on experimental observations, design guidelines and data collected literature. It is capable of predicting both failure load and failure mode of flexural strengthened and end anchored beams. The model was compatible with experimental results of current study as well as experimental results collected from literature. Two papers were published from the work of this study and are attached in appendix E.
item: Thesis-Full-text
Development of light weight cement blocks with bottom ash from coal fired thermal power plants
Savitha, R; Nanayakkara, SMA
In the Nuraicholai coal fired thermal power plant, 7500 MT of coal per day is burnt producing 750 MT and 75 MT of two main waste products fly ash and bottom ash respectively. Fly ash is used in cement manufacture, but bottom ash is presently regarded as a waste material. However, there is a possibility to convert bottom ash to a value added material. This thesis presents findings pertaining to the feasibility of using bottom ash as a replacement of sand in producing light weight cement blocks. Chemical analysis carried out using Atomic Absorption Spectroscopy on Nuraicholai power plant bottom ash waste showed that the harmful elements present such as As, Pb, Cr, Cd, Cu, Ni and Se were within internationally specified toxicity limits for soil. It was found that bottom ash at oven dry condition had a loose bulk density of 600 kg/m3, which is about 40% that of river sand which has a nominal loose bulk density of about 1450 kg/m3. Important physical and mechanical properties such as compressive strength, water absorption, density, accelerated erosion resistance and drying shrinkage & wetting expansion were tested for blocks produced by partly or fully replacing fine aggregate with bottom ash. Heat conductivity of blocks produced with bottom ash was found to be less than the good quality conventional cement blocks available in Sri Lanka. Comparatively, performance of the bottom ash blocks was very good and comparable with conventional cement blocks produced with river sand and quarry dust. Further, trials were carried out with river sand, crushed rock sand and coarse aggregate in order to find out optimum mix proportions and to investigate the feasibility of medium scale production of bottom ash blocks using a conventional type of block making machine. The optimum mixes which give strength, density and water absorption of desirable amount were found with Cement, Quarry dust, Bottom ash and 5-10 mm crushed rock aggregates.
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Establishment of dry weather flow in Kalu ganga under climate change scenarios
Rajapaksha, RWCN; Wijerathne, N
Kalu Ganga basin is one of the most important river basins in Sri Lanka which covers a major portion of the wet zone and carries the highest discharge volume into the sea annually. Therefore it has been identified that, Kalu Ganga is the main source of water for potable water supply schemes especially for the Greater Colombo area. It is the dry weather flow which determines its potential as a source of water for potable water supply schemes with no major ‘at the source storage’. This study is focused on the analysis of low flow due to climate change. The objective of the study is to establish low flow conditions in the Kalu Ganga basin under different climate change scenarios. Effect of the predicted climate change scenarios on the low flows can be taken into account by using Statistical downscaling with emission scenario consideration. Statistical Downscaling Model (SDSM) is used for the downscaling of GCM data. Downscaling of GCM data using SDSM Global Circulation Model data of Hardley Center Coupled Model 3 (HadCM3) is used under both A2 and B2 emission scenario as the raw data. A variation of future rainfall is analyzed with observed data. Catchment runoff is predicted using a MIKE11 NAM based hydrological model for 50 years. Frequency analysis is conducted for measured and predicted flow data to establish low flow values due to climate change impacts. Reduction of low flow in Ellagawa station about 6% and Millakanda Station about 4% in 50 year return periods. It is about 1% for other return periods in both stations. Impact of climatic change is high for the events with high recurrence interval. Hence it is not recommended to extract water during dry period. Therefore, having an appropriate storage system to cater the required demand during dry season is needed.
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Modelling of the deployment behaviour of highly compacted thin membranes
(2016-09-14) Liyanage, PM; Mallikarachchi, HMYC
Space structures such as solar sails, solar reflectors, and sun shields have very large surface areas. Hence they require deployable methods to be stored and transported out of the earth’s atmosphere in limited cargo capacities available in launch vehicles. A deployable structure changes its shape and geometry to a compact state with the use of folding patterns for convenience in packaging and/or transporting. Ground testing of deployable structures using physical models requires a representative environment, i.e. a zero gravity environment, which can consume a lot of time, effort, and cost, giving rise to the requirement of simulations carried out in a virtual environment. This research develops a modelling technique which can be used to simulate the deployment behaviour of membrane type deployable structures using a commercial finite element analysis software. Commonly used spiral folding pattern was used to demonstrate the modelling technique. Modification for the fold line arrangement of spiral folding pattern to account for effects caused by membrane thickness; modelling the crease behaviour with the use of rotational springs; and robustness of the analysis indicated by energy histories were three main aspects considered when developing the modelling technique. Spiral folding pattern was modified by finding the arrangement of nodes in the folded state of the model by providing sufficient offset between planes and checking the ability of the structure to deploy into a plane sheet. This modification was proposed for modules with regular polygonal shaped hubs. Proposed modification was verified with the use of a paperboard model which had a square shaped hub of 10 mm × 10 mm, 15 nodes in a single spiral, and a thickness of 0.28 mm. Crease stiffness of Kapton Polyimide film was determined comparing data available from an experiment carried out at the Space Structures Laboratory of California Institute of Technology and results of finite element models developed to simulate the experiment. Finally two finite element models were made from the proposed technique and results of these analysis were discussed on importance of incorporating crease behaviour in finite element models, important aspects of their deployment behaviour, and robustness of analysis. This research has successfully developed an approach to modify the fold line arrangement of the spiral folding pattern with regular polygonal shaped hubs to account for the geometric effects caused by membrane thickness and a robust technique to model the deployment behaviour of membrane type deployable structures. Crease stiffness of Kapton Polyimide films was modelled as a rotational spring, where the resisting moment is considered to be proportional to the opening angle near the crease. Comparing results of two finite element models, with and without crease stiffness, showed that crease behaviour affects the deployment performance of these structures significantly, and hence it is important to be included in simulations.
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TSUNAMI RISK ASSESSMENT FOR EARLY WARNING AND IMPACT MITIGATION
(2016-05-23) Samarasekara, RSM; Hettiarachchi, SSL; Ratnassoriya, AHR
An effective, accurate, reliable and rapid version for the Indian Ocean Tsunami Warning System (IOTWS) is stretches back over several years to integrate with the tsunami forecasting and early warning framework. A brief outline is presented to enhance the capacity to cope with an emergency situation in scientifically rigorous manner. 2005 March, 2007 September, 2012 April etc. false tsunami warnings recall the need for effective implementation of the IOTWS with operational robustness to initiate tsunami mitigation program and to be prepared for future potentially destructive tsunamis in the region. Use common and agreed formats for information exchange, address common service requirements, standard operating procedures and international commitment strive to satisfy the public safety in a tsunami emergency. Develop all elements in order to conduct a tsunami hazard assessment study for a city along the coastline of Sri Lanka, operating within the framework of template for coastal cells in deep water adopted by the RTSP. All material available from the activities of the former Working Group on Modelling, in particular development of data bases along the fault line for tsunami forecasting and deep water modelling was reviewed to study the existing performance criteria of the tsunami warning system by communicating with RTSPs to clarify important issues. Preparation of a Case Study for the port city of Galle will illustrate the capability that serves real time operational needs, hazard/risk assessment needs and research/development opportunities through the use of a standard tsunami forecast system that includes tsunami characterization, measurements and forecast models. This study will be the hazard assessment for the above study. Unfortunately, many people living alone the shore facing climate change impact adversary. This incessant struggle between humans and nature need to be stabilized via short – and long – term approaches. This research provides an excellent cross reference and strong awareness of approaches adapted in IOTWS thus educating a wider stakeholder base on the said approach.
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Performance of green roofs in tropical climatic conditions
(2016-05-02) Wijerathne, SN; Halwatura, RU
Growth ofthe world urbanization has been extensively accelerated since past few decades. With the increasing urbanization, the land with permeable layers and moist have been altered. As a result, urban heat island phenomenon has taken place, making the temperature in the cities to be higher than the country sides. Heat island effect in cities is mainly because of non-natural heat absorbing materials use in buildings and other man made structures. Natural greenery in the cities was replaced by concrete yards and most of the cities urbanizing with more and more concrete. Since there is no space to grow, adding greenery to cities is also an issue. Having greenery over the roof or planting on roofs are now becoming popular in many countries. Green roofs playa major role as a sustainable solution to minimize the heat island effect. This research discusses about the effects on the surrounding temperatures, if the existing flat roofs in the Colombo city, the capital of Sri Lanka, are replaced with green roofs. The reduction in the temperature in the atmosphere was calculated using actual measurements on small scale models and computer simulation. These findings were coupled with the energy balance of the city. From the results obtained, it can be clearly shown that there's a significant reduction in the temperatures, in the city when compared to the prevailing condition. The forecasted condition proves that the foreseeable problem of urban heat island effect with the future developments can be drastically reduced with the introduction of green roofs. Another problem the world is facing today is energy crisis. Because of that world is now focusing on the sustainable cities. The contribution of the green roofs towards the energy cost saving when it is implemented in the city level in the existing flat roof slabs is calculated. A Derob modeling is done and the AlC loads are obtained for different roof types throughout the year and with the actual roof areas obtained for the city the energy cost saving is calculated. The energy cost saving obtained was 12%. However when it incorporates with the actual practice the desires of the population also should be analyzed. Identifying the implementation possibilities of the green roofs in the city also is vital to achieve these identified benefits in the future. This was achieved through a detailed questionnaire survey. With questionnaire survey it was found that the awareness of the green roofs is 56.8% and the willingness to spend for a green roof is less than 20% than the existing cost for an asbestos roof.