CERS - 2021

Permanent URI for this collectionhttp://192.248.9.226/handle/123/17780

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item: Conference-Abstract
3D full field deformation measurement using digital image correlation
(Department of Civil Engineering, University of Moratuwa, 2021-11) Lowhikan, SS; Mallikarachchi, HMYC; Hettiarachchi, P
3D deformation and strain are crucial parameters in engineering design and construction. Precise 3D full-field measurement is useful in identifying the response of the structure under a given loading condition. Digital Image Correlation (DIC) is a non-contact optic-based technique that may prove to be ideal for full-field deformation applications. It has the potential to become an inexpensive, simple, and accurate solution for deformation measurement. All DIC measuring systems now available consist of expensive software packages and experimental facilities which are difficult to access. Therefore, a cost-effective method must be developed to use in the local context efficiently. This research mainly focuses on the development and validation of the cost-effective precise noncontact- based deformation measurement technique. In the proposed method, 3D full-field deformation of the deforming object is measured using two digital cameras and an image processing toolbox available in the MATLAB commercial package. Further, the proposed method efficiency is enhanced by developing it as a standalone application, which can be installed and used by any technician conveniently and utilized for various laboratory Civil Engineering applications. Enhancing the proposed DIC algorithm to improve resolution in 3D applications and extending to phase-changing materials and developing Graphical User Interface (GUI) and general guidelines to be used by a technician were defined as objectives of this research. The proposed measuring system consists of two digital cameras mounted on a rigid frame as it is targeted to capture the specimen and connected to a computer. A random speckle pattern must be applied on the specimen’s surface to track the deformation. The proposed image processing algorithm was developed in MATLAB by using a computer vision toolbox. Later Graphical User Interface was developed using MATLAB App Designer. The developed system was used to obtain the results and validated for rigid body motion tests of concrete cube and cylinder, compression test of concrete, uni-axial tensile test of a dog bone aluminium specimen and shrinkage cracks of mortar experiments. In conclusion, a cost-effective and reliable measurement system was developed by using DIC techniques and MATLAB computer vision toolbox, with its performance validated experimentally by assessment of measurements of the in-plane strain of materials. Even though it has some limitations, the developed algorithm and application can be effectively used for laboratory-scale Civil Engineering related experiments. Also, the application that was developed can be handled by technicians who do not have much knowledge nor understanding of programming languages. The Graphical User Interface that was developed is easy to use and saves considerable time. The performance of the system that has been developed can be assessed and improved for greater precision.
item: Conference-Abstract
Advanced structural health monitoring system for bridges in Sri Lanka
(Department of Civil Engineering, University of Moratuwa, Sri Lanka., 2021-11) Rajapaksha, D; Lewangamage, CS; Vishnu, P; Hettiarachchi, P
Bridges are a critical component of the transportation infrastructure system because a failure in a particular bridge may affect a wide range of areas adversely. Also, the intensity and frequency of natural shocks and stresses that can affect the performance of the bridges, such as earthquakes, floods, and tsunami have rapidly increased during the past few years, which increases the vulnerability of bridges by combining with aging. Hence it is crucial to monitor the current health of bridges so that devastating failures could be avoided by following a structured maintenance program. In that case, advanced Structural Health Monitoring (SHM) systems that are rapidly developing for past decades with the development of IoT, have been used for bridge monitoring purposes in other countries. However, the condition of the bridge monitoring system is not so developed in Sri Lanka yet. Also, the commonly used methods such as visual inspection and traditional tethered methods are incorporated with some drawbacks. Therefore, the requirement for an advanced SHM system for bridge monitoring in Sri Lanka has been raised. In this study, a low-cost wireless synchronous sensor network developed by the Department of Civil Engineering, University of Moratuwa was applied and monitored on a bridge as a pioneering step of implementing an advanced online SHM system for bridges in Sri Lanka. Here, the synchronous vibration time history of the structure was measured using the sensor network with high accuracy. After a filtration process, the data was applied for calculating the experimental modal parameters such as natural frequencies and mode shapes using Fast Fourier Transformation (FFT) and peak picking method. Finally, the experimental results were compared with the results of Finite Element Analysis (FEA) through the Modal Assurance Criteria (MAC). The MAC analysis showed values greater than 0.84 for the first four modes shapes which indicates a good correlation with the experimental results and the FEA results. Furthermore, the measured acceleration data was used to assess the serviceability state of the bridge as well.
item: Conference-Abstract
Analysis of multi-day extreme rainfall events in Kelani River basin
(Department of Civil Engineering, University of Moratuwa, 2021-11) Chathuranga, GK; Fernando, WCDK; De Silva, PKC; Hettiarachchi, P
Floods, one of the major disasters in Sri Lanka occur not only due to a single daily rainfall but due to multiday rainfall events. Thus, to safeguard the properties, analysis of the multiday rainfall events is more relevant than analysis of one-day rainfall events. The objective of the research is to identify the temporal rainfall pattern in the Kelani River upper catchment (using Canyon, Castlereigh, Laxapana, Norton and Hatton - Meteorological stations) for conducting rainfall frequency analysis using data from the annual maximum (AMAX) series. The preparation of the data series is done by using the Block Maxima tool and the trend pattern is identified with the Mann-Kendall test. Then selected potential candidates for frequency analysis using the L-moment method and selected the best fit distribution by using the goodness of fit test. The final outcome is to identify the Extreme rainfall values for different return periods. According to Manne Kendal test results, all series have increasing trends but they are not significant, except for Norton PX3D which has a significant increasing trend. Hatton Kotagala PX3D has a decreasing trend that is not significant. For all AMAX series skewness is positive, In the kurtosis for all AMAX series except PX2D and PX3D in the Canyon, its tails are longer and wider, and often its central peak is higher and sharper(leptokurtic). For AMAX series PX2D and PX3D in the Canyon, its tails are shorter and narrower, and often its central peak is lower and broader (platykurtic). Gamma (G), Lognormal (LN), and Weibull (EV3) were selected as potential candidates for frequency analysis. From KS test results Gamma distribution fitted to 46% of the series, while Lognormal and Weibull fitted to 27% of the series. The maximum PX1D is 440 mm in 1989 at Laxapana and for the PX2D series, the maximum value is 831 mm in 1989 at Laxapana. It was observed that the maximum PX3D is 924.7 mm in 1989 at Laxapana. The average ratio between 3-day maxima to 1-day maxima is 2.1 and the ratio of 2-day to 1-day becomes 1.9. This finding greatly helps to estimate PX2D or PX3D in the context of engineering design when there is a lack of data. It is seen that there is an increasing trend at all stations except Hatton-Kotagala PX3D. However, a significant increasing trend was detected at Norton PX3D at a 5% level of significance. For all other stations, AMAX shows no significant trends. In general, it can be argued that the Kelani River Upper catchment has an increasing trend but is not significant for annual maximum rainfall series of one day, two days and three days at a 5% level of significance. The Gamma distribution is the best-fit distribution for most of the one-day annual maximum rainfall series. However, for two-day and three-day series all three distributions - Gamma distribution, Lognormal distribution, and Weibull distribution can be considered as equal. In low return periods such as 25 years and 50 years there is no such difference in return levels. However, for larger return periods, the discrepancy is higher. The accuracy and reliability of the results can be further improved by increasing the length of records and the number of gauging stations. If four- or fiveday events are considered in the analysis, a better idea about the extreme events can be obtained and how they combined with the flooding condition. These results can be used for flood mitigation projects, for statistical estimation of probable maximum precipitation, better models of risk and damage can be developed from multi-day extreme rainfall events and flooding.
item: Conference-Abstract
An application of a cell transmission model using crowdsourced data for expressway monitoring
(Department of Civil Engineering, University of Moratuwa, 2021-11) Wijepala, WMRV; De Silva, D; Hettiarachchi, P
With the increasing traffic congestion in alternative roads, the demand for expressways is increasing rapidly in Sri Lanka. With this increase in demand, traffic management systems are needed for expressways. Deviating from traditional expensive methods of traffic data collection, a more economical and reliable data collection method is needed for developing countries. This study aims to develop and apply a Cell Transmission Model which was first introduced by Carlos F. Daganzo in 1993. The crowdsourced traffic data collected by Google Distance Matrix API has been used. An expressway section was selected and divided into number of sections referred as cells, which were defined with different cell lengths according to the location of the expressway section. The average speed of each cell was collected from Google maps using the MTRADA platform to identify the traffic condition of the selected expressway section, every 5 minutes. The speed data collected were represented in a spatiotemporal graph. Different cell lengths were tested to identify the optimum cell lengths for the model that would allow to identify variations in speed changes. A manual flow data collection was also collected to study the trend between manually collected flow data and speed data collected from M-TRADA. 2 types of cells were used as 200 m and 250 m as normal cells and 400 m and 500 m as doubled cells. Data were collected for both the types simultaneously. According to the comparison done for both the cell types, the normal cells show sufficient information of speed changes than the doubled cells and the cell size has to be at minimum 200 m at the on/off ramps, near sharp curves and near interchanges, while a cell size of 250 m would be sufficient to for cells within the main lanes. This model is more useful for expressways with higher demand. A user interface is proposed for a web application that can be developed using this model for real-time traffic monitoring purposes. Because of the simplicity of the model, even non-expert users will be able to use this web application.
item: Conference-Abstract
Characterising the self-opening behaviour of single creased Kapton polyimide films
(Department of Civil Engineering, University of Moratuwa, 2021-11) Navaratnarajah, S; Mallikarachchi, HMYC; Hettiarachchi, P
Use of thin folded membranes for deployable structures is becoming increasingly popular especially in aerospace applications such as a deployable solar arrays, sun shields, and solar sails. The folding and compaction process of thin membranes, which introduces permanent, nonrecoverable, localized plastic deformation, changes the geometric shape and material properties. Therefore, precise prediction of folding and deployment behaviour is essential for the mission's success as incorrect folding, storage, and deployment could result in damaging the membrane or not achieving the expected deployed configuration. Virtual simulation is a feasible solution in comparison with physical testing which requires reduced gravity, friction, and air-drag-free environment in design optimization of these structures. However, accurate idealisation schemes will significantly reduce number of elements meaning lower the degrees of freedom and hence reduce the computational cost. Therefore, a proper understanding of the mechanics of creased membrane structures is the key, in formulating such idealisations. The underlying mechanics in the deployment of creased membrane structures from the folded state to the deployed state involves two phases. First, the structure self-opens from the fully folded state to the stress-free stable state. It then requires an external force to deploy from stress-free state to fully deployed state. This can be referred to as forced opening. The focus of the previous studies was limited to the characterisation of crease behaviour during forced opening but not the self-opening which is also crucial in the design of gossamer structures. In this research, an attempt has been made to characterise the crease mechanics of single creased thin Kapton polyimide membranes during their self-opening behaviour using two different experimental approaches. One experimental study investigates the rotational motion of a panel in a single creased membrane immediately after creasing where angle, angular velocity, and angular acceleration variation were obtained to develop the moment-rotation response. The second experimental study evaluates the moment-rotation response of crease during quasi-static folding of the single creased membrane once it achieved the stress-free stable state. It has been found that the moment-rotation response during the self-opening behaviour shows a linear trend for all thicknesses considered. The effect of membrane thickness and width on the crease rotational stiffness was also investigated in the experimental study. Accordingly, crease stiffness increases with increasing thickness and is independent of the width of the specimen. A simple analytical study was performed to predict the rotational stiffness of the crease which shows a good qualitative agreement with physical experiment results. Finally, the results from the self-opening study were combined with the forced opening study which was done by previous researchers. Based on the results it is reasonable to assume the fold-line stiffness to be linear during the whole deployment with a constant crease stiffness. This value can be easily incorporated as spring stiffness in the finite element model by idealising the crease region as a rotational spring to reduce the computational cost.
item: Conference-Abstract
Characteristic analysis of embedded wave barrier material beside railway tracks
(Department of Civil Engineering, University of Moratuwa, 2021-11) Abiram, P; Hidallana-Gamage, HD; Hettiarachchi, P
Rail transport is one of the most effective modes of transporting goods and people among various access points. It has several benefits compared to some of the other modes of transport, such as safety, cost effectiveness, time saving, and high capacity. Forces from the result of passing vehicles and irregularities at the wheel-rail interaction, penetrate through wheel into the track, and generates vibration. The scenarios of increasing traffic congestion and civil infrastructure development in Sri Lanka, have led to the concern about the improvement of railway transportation free from propagation of vibration through ground. Using embedded barrier material within a trench beside the railway track is an effective active control strategy practiced in most of the Railway transportation sectors around the world. In this research, characteristics of the material which is used as a vibration controlling layer embedded beside the railway track within the subsoil are analysed. Initially a finite element model of a railway track was developed, and then it was validated with the field vibration measurements available in the literature. Later a parametric study was carried out by varying the properties of the vibration controlling layer within the subsoil. The vibration characteristics were compared at 2 and 3 m depths, for different Elastic modulus, density, and void ratios of the material. It was evident that barrier material with lower elastic modulus provides a better vibration screening performance. If the available barrier material has a high elastic modulus, it should be constructed deep enough to provide a better vibration screening performance. For a given depth of an embedded barrier layer, there will be an optimum unit weight, which provides a high performance of screening. It was also found that, 2 m deep barrier provides better performance than the 3 m deep barrier for a given unit weight. Increasing the void ratio will increase the pores inside the material, and hence will increase the performance of the barrier. A shallow barrier provides better performance up to a certain value of void ratio, beyond which the performance is independent of the depth of the barrier. Overall, findings of this research elaborate the optimum material characteristics of a vibration controlling layer for train induced ground vibration in different depths.
item: Conference-Full-text
Civil Engineering Research Symposium 2021 (Pre Text)
(2021)
item: Conference-Abstract
Combining water and environmental footprint methods for life cycle assessment of run of the river type mini/micro hydropower generation
(Department of Civil Engineering, University of Moratuwa, 2021-11) Pihillanda, VSB; Rajapakse, RLHL; Hettiarachchi, P
Hydropower is popular as one of the most environmentally friendly renewable energy sources. However, with the expansion of knowledge about footprint methods, it has been identified that there are considerable carbon, water and ecological footprints in hydropower schemes that are not adequately recognized based on commonly available tools and methods for overall impact assessment. Among these tools which assess the environmental impact quantitatively, the water footprint methods assess the water consumption (alias water loss) per unit of power produced at a hydropower plant. There are three methods of assessing the water footprint of hydropower plants namely, Gross Evaporation Method (WF1), Net Evaporation Method (WF2) and Net Water Balance Method (WF3). All three methods have been developed and used for hydropower plants connected to major reservoirs but have not been used for run-of-river (ROR) type mini/micro hydropower plants. Identifying this research gap, along with the fact that the Ceylon Electricity Board has planned to increase the mini/micro hydropower production in their Long-Term Generation Plan, this study has investigated the ability to apply the existing water footprint methods to ROR type mini/micro hydropower plants. Furthermore, their ability to relate to the Sri Lankan context as a viable tool in mini/micro hydropower plant designing phase is also investigated. The existing WF methods were applied to three selected mini hydropower plants in Seethawaka Ganga Sub-basin in the Kelani River Basin. To conduct the application, the daily streamflows at the weir locations were derived using a calibrated HEC-HMS model and available meteorological data. Then a correlation was synthesized between the daily streamflow at the weir and daily energy production of the mini hydropower plants based on the characteristics of the installed turbine and generator capacities. Simultaneously, the water losses were estimated using meteorological data and plant specific data which were extracted from project documents and using GIS tools. With the derived energy generation and estimated water losses, the daily, monthly, and annual WFs were calculated and their ability to reflect the ROR nature, the scale of the plant (i.e., mini/micro scale) and the Sri Lankan context were investigated. Based on the findings of the detailed analysis, it was concluded that the most appropriate water footprint method that reflects above-mentioned characteristics is the Mean Monthly Water Footprint of Gross Evaporation Method. Furthermore, a quantitative as well as a qualitative sensitivity analysis was carried out to identify all possible variations that may affect the outcome and the ability to integrate water footprint into ecological footprint evaluation is discussed. The study findings will be useful in the proper evaluation of overall impacts and for decision making in the implementation of future mini/micro hydropower generation plans.
item: Conference-Abstract
Composite effects of pozzolans in producing high strength recycled aggregate concrete
(Department of Civil Engineering, University of Moratuwa, 2021-11) Fernando, AM; Gamage, JCPH; Hettiarachchi, P
Over the years, the unceasing growth and development in the construction industry has resulted in both positives and negatives. The extensive use and disposal of many of the materials used in construction have resulted in the depletion of natural resources, together with piling up of large amounts of construction and demolition waste in landfills, causing adverse effects on the environment, the economy as well as society. The most extensively consumed material in the construction industry can be identified as concrete. Procurement and transportation of raw materials for cement and aggregates which are the two major constituents used in concrete production add significant disturbances to the ecological system. Thousands of research studies have shown the feasibility of using recycled aggregates to produce both normal and high strength concrete with comparable properties to conventional concrete. However, it requires a more allinclusive approach in producing an environmentally friendly solution. This paper discusses the procedure followed in producing cost effective and economical high strength concrete through the composite use of pozzolans namely fly ash, silica fume and rice husk ash (RHA), in both stages of aggregate treatment and concrete production. Results from aggregate testing showed a 26%and 59% reduction in aggregate water absorption and porosity, respectively. Further, enhancements in terms of aggregate specific gravity and crushing value were obtained. Concrete which contained RHA in both stages, attained a compressive strength of 55.4 MPa, which was even higher than the control mix containing natural aggregates. The same mix of concrete showed a 12% increase in its surface resistivity. This indicates the possibility of achieving high strengths, even with the use of RA derived from parent concretes of lower grades, and not many studies have focussed on this aspect of high strength recycled aggregate concrete production (HS-RAC).
item: Conference-Abstract
Compressibility characteristics of unsaturated soil
(Department of Civil Engineering, University of Moratuwa, 2021) Krichikeshan, I; Kulathilaka, SAS; Hettiarachchi, P
Conventional Terzaghi's consolidation theory is developed for saturated soil. However, in practice the concept is used with unsaturated soils as well. The behaviour of unsaturated soils is quite different due to the presence of the air phase and the contractile skin- the boundary between air and water phases. In many places in the country residual soils formed by the weathering of parent metamorphic rock are present at the surface level and there is a zone of unsaturated soils just below the ground surface. Loads from many structures are applied on this zone and the understanding of the compressibility of this zone is very important. Also, there is high variability in this zone. The objective of this research is to identify the variation of compressibility characteristics of different soils with the saturation level. Due to the existence of air phase in unsaturated soil, excess pore water pressure is not equal to the load applied when the soil is compressed under an undrained loading condition. To get an accurate reliable equation we need to consider both pore water pressure and pore air pressure. If the excess pore air pressure and excess pore water pressure are allowed to dissipate, the excess pore water and air pressure will dissipate gradually with time. The volume change of the unsaturated soil is not equal to the water drainage in unsaturated condition. And also, it is necessary to consider the saturation level. The main parameter that causes the difference from saturated soils is matric suction. As such in this research a controlled uniform saturated sample is obtained, and it was brought to equilibrium under different matric suctions. The compressibility characteristics of the same soil under different matric suctions are evaluated. The parameters are evaluated under the framework of Terzaghi model. An attempt was made to establish a relationship between the matric suction and the consolidation parameters. Identical samples were tested on conventional Oedometer and a Rowe Cell of diameter 75 mm. The void ratio, natural moisture content, compressibility index are the features which can be obtained from standard Oedometer consolidation test and Rowe cell consolidation test. Available data states that the compressibility characteristics of unsaturated soils are usually very nonlinear and cannot be considered in some conditions. Compressibility of unsaturated soil depends on many factors. Some of them include particle size distribution, saturation level, temperature, permeability. Compression index (Cc) and Recompression index (Cr) decrease in the initial stage and then increase with matric suction. mv value for the saturated sample was greater than unsaturated soil and with the increase of stress level, the mv value of all the samples decreased.
item: Conference-Abstract
Development of a plastering mortar using waste bagasse and rice husk ashes with sound mechanical and thermal properties
(Department of Civil Engineering, University of Moratuwa, 2021-11) Srikanth, G; Gamage, JCPH; Hettiarachchi, P
The concept of using cleaner production technologies has become prominent in the present context for achieving sustainability in construction. It has been proven that by incorporating agricultural waste as cement replacement, mechanical and durability properties of the resulting mortar have been enhanced. A comparative study on the mechanical, thermal, and environmental performance of a newly developed lightweight mortar containing agro-wastes namely Bagasse Ash (BA) and Rice Husk Ash (RHA) were investigated. Ordinary Portland cement was partially replaced by BA at dosages of 0%, 5%, 15%, 20%, and 30% and RHA at dosages of 0%, 5%, and 15% by weight. A detailed investigation was carried out to determine the best suited material mix which can achieve very good material properties. Results indicated that the mixtures with the replacement percentages up to 30% by both BA and RHA for cement had compressive strength confined to the standard recommended range (~5.2 MPa) while maintaining the adequate water absorption and acid alkaline resistance. This indicates that BA can be used to replace the cement up to 30% and BA and RHA of each 15% of cement replacements also can be used to manufacture the mortar for wall plaster and addition of 30% BA as a partial replacement for cement improved the thermal performance by causing a decrease in the thermal conductivity about 33%. However, the combination of BA and RHA (15% each) decreased the thermal conductivity up to 31% compared to the conventional mortar and results indicated that acid resistance also increased with the increase the percentage of BA and RHA, Further, the assessment of environmental impact reveals a noticeable reduction in embodied GHGE with the increasing replacement of BA and RHA in mortar. When the cement in conventional mortar was substituted with 30% BA and, 15% BA and 15% RHA, both cases reduced the CO2 emissions by about 28% than the control mix. The cost of control for both mortar containing 30% BA and mortar containing 15% BA and 15% RHA production is 16.6% of conventional mortar mix. However, the energy to produce BA mortar is less than BA and RHA mortar. Thus, BA falls more under the prospective of energy effective, cost-effective, and environmentally friendly construction materials.
item: Conference-Abstract
Development of an alternative approach for bored and cast in-situ pile design using PDA test results
(Department of Civil Engineering, University of Moratuwa, 2021-11) Kaushalya, AAS; Nawagamuwa, UP; Hettiarachchi, P
Many pile designs are done as bored cast-in-situ end bearing pile designs in Sri Lanka and the reason for that is the availability of hard bedrock at relatively a shallow depth compared to other countries. These designs are mostly done using ICTAD/CIDA guidelines. However, many researchers have identified some issues that are generated with conventional pile design methods and construction procedures of the piles. Test piles are widely being used to check the accuracy of assumptions that are generated with the designs. End bearing and skin resistance of the rock are only considered in most of the pile designs in Sri Lanka. Because of this phenomenon, skin resistance of soil layers that have a high SPT “N” value is not considered for the capacity estimation. In this study, the applicability of estimation of carrying capacity of the pile considering the soil layers which have higher SPT “N” value was verified. Therefore, a comparative study was conducted together with two main research objectives. It was required to evaluate which design procedure is more effective when comparing the estimation of the pile capacity considering all the layers which have SPT “N” values more than or equal to 15 (as criteria 1) or the pile capacity only considering the skin and toe resistance in the bedrock (as criteria 2), and a comparison of the estimated allowable carrying capacity values according to the ICTAD/CIDA and Euro code 7 guidelines with the actual allowable carrying capacity values which were taken from the CAPWAP analysis of PDA test results was also considered as a primary objective in this study. As per the methodology, required data and information were gathered and the soil parameters were calculated by obtaining corrected SPT “N” values. Thereafter, allowable carrying capacity according to ICTAD/CIDA guidelines and design carrying capacity according to Euro code 7 guidelines were estimated for both criteria. The difference between the estimated values of both criteria was represented as a percentage. After selecting more suitable and applicable criteria, the capacity values which were estimated using those criteria were compared with actual allowable carrying capacity values. According to the analysis, the difference between the estimated values of both criteria were approximately ranged between 6% - 65% for the estimation according to ICTAD/CIDA guidelines and 16% - 150% for the estimation according to Euro code 7 guidelines. Therefore, the estimation of the pile carrying capacity considering all the layers which have SPT “N” values more than or equal to 15 is better predicted than the estimation of carrying capacity of the pile only considering the skin resistance of rock and end bearing of the pile. As per the comparison of the actual and estimated allowable capacities, it is possible to obtain overestimations or underestimations that will rely on the assumptions made about the properties of soil and rock layers. Therefore, the accurate soil parameters and properties should be maintained in estimations and, the geotechnical investigation of the site should be more accurate.
item: Conference-Abstract
Development of design guidance for circular reinforced concrete columns incorporating crack width
(Department of Civil Engineering, University of Moratuwa, 2021) Jayaweera, GCS; Hidallana-Gamage, HD; Indrajith, WPR; Hettiarachchi, P
The maximum crack width of Reinforced Concrete (RC) structures should be controlled for satisfying the serviceability and durability requirements of the civil engineering structures. Therefore, care must be taken at the initial design stages for maintaining the possible crack widths within a permissible range which has been specified under the design standards. However, the crack width analysis of RC structures is not easy because of the complexity of the parameters which affect the crack width. If crack width calculation is skipped, the width of the cracks in real concrete structures can be larger than the maximum limiting allowable value. Circular RC columns and piles are widely used structural components in modern civil engineering construction projects. As an example, circular RC piles and columns can be seen in many expressway construction projects in Sri Lanka to support viaduct structures. The main aim of this research is to develop design guidance for circular RC columns to estimate the crack width. In the Sri Lankan construction industry, there is no specific simplified guidance in terms of charts and tables for crack width estimations of circular RC columns. Hence, it is important to develop such design guidance for circular RC columns. Although there are a variety of applications of circular RC columns in the industry, this research deals with the crack width analysis of circular RC columns in straight viaduct sections. A comprehensive study was carried out regarding the behaviour of the cracks in circular RC columns in viaduct sections as per the design standard, BS 5400. Autodesk Structural Bridge Design software was used to perform crack width estimations, and MIDAS Civil software was used to do the Finite Element (FE) analysis and validation process. The crack width can be estimated to a 0.01 mm accurately by using the charts developed in this research. This design guidance is simple to understand, and use. Hence, engineers can perform their preliminary crack width estimations with less effort using correctly specified methods. Crack width estimation charts were developed for both uniaxial bending and biaxial bending cases of short circular RC columns with a diameter of 1.5 m, C 25/30 concrete, a nominal cover of 45 mm, and the main rebars all of the same diameter. According to the parametric study done for the circular RC columns subjected to uniaxial bending, the following details were found. Crack width reduces with increasing bar diameter and number of main rebars. Crack width is low in the columns with high-grade concrete. When the ratio of Mq/Mg as defined in BS 5400 is decreased, the crack width also decreases. A significant variation of the crack width can be seen in the cases where, the ratio, Axial load (ULS)/(Column diameter)2 is in the range of 0.5 to 2.5 N/mm2. The width of the crack is significantly higher in the case of having higher bending moments with low axial forces. This research can be extended to develop design guidance for estimating the crack width following latest standards such as Eurocodes and produce more charts by accounting for the requirements of the design engineers. The comprehensive design charts developed in this research will be useful in estimating the crack widths in circular RC columns without the need to follow time-consuming methods. Therefore, the findings of this research will be helpful to enhance the efficiency of the design work.
item: Conference-Abstract
Development of sandwich roof panels: a review
(Department of Civil Engineering, University of Moratuwa, 2021-11) Bandaranayake, SS; Gamage, JCPH; Hettiarachchi, P
Sandwich panels (modular panels) promote optimal solutions to some major issues prevailing in the construction industry such as increased energy consumption by building elements, excessive disposal of construction waste and unproductive time spent during construction. Hence the inclination towards sandwich elements has been increased vastly deviating from conventional building construction materials and methods. However, the potential of using locally available natural materials for the development of sandwich panels is a salient sustainable approach that needs to be addressed. The research methodology was composed of a detailed literature review followed by a series of thermal simulations using a commercially available finite element analysis programme. The potential materials used in modular panels and key properties of sandwich panels which include mechanical, thermal and sound insulation properties were identified. Moreover, various test methods followed, and standards specified to investigate the mechanical, thermal, and acoustic insulation properties were also discussed. Secondly, the possibility of using coconut fibre as a locally available natural alternative core material to polyurethane core of sandwich panels has been evaluated using the aforesaid thermal simulation software based on the material properties obtained from literature. The study identifies coconut fibre as a potential alternative core material for sandwich roof panels which reflects similar thermal behaviour to polyurethane. However, these results can be further validated, and panels can be optimized structurally by performing further experimental studies based on the test methods and standards identified in the study.
item: Conference-Abstract
Effect of a shear key on the behaviour and stability of cantilever type retaining walls
(Department of Civil Engineering, University of Moratuwa, Sri Lanka., 2021-11) Gowshikan, A; De Silva, LIN; Hettiarachchi, P
Retaining walls are categorised into several types, of which cantilever retaining walls are the commonly used retaining wall type. The stability of these walls should be ensured for its longterm use without any anticipated failures. A retaining wall can fail due to four main failure mechanisms: sliding, overturning, bearing capacity, and deep-seated failure. Shear keys are the structures incorporated in the cantilever retaining walls to increase their resistance to sliding, thus, increasing the Factor of Safety against sliding. The development of passive earth pressure due to the soil in front of the shear key will generate an additional resistance against sliding. This study aims to identify the optimal location and depth of the shear key to yield maximum use from it. Both the theoretical approach based on limit equilibrium and numerical modelling have been adopted in the analysis. Limit equilibrium analysis was carried out using the Excel spreadsheet application, and two different scenarios were considered based on the distribution of lateral loads due to active soil conditions. Rankine's method was used for active and passive earth pressure computation. For the shear key, three different locations were considered: at the toe, middle of the base, and heel, and five different depths were considered: 0.4 m, 0.6 m, 0.8 m, 1.0 m, and 1.2 m. Soil strength properties were taken by referring to the commonly used backfill soil materials in Sri Lanka. The design soil parameters considered for the analysis were calculated using BS 8002:1994. From the Limit Equilibrium approach, the values of Factor of Safety (FOS) against sliding and overturning, varying with the shear key's depth and location, were obtained as graphical representations. Finite Element Analysis was carried out using PLAXIS 2D software to analyse the variation of the overall stability with the increasing depth of the shear key and validate the location of the point of rotation assumed in the limit equilibrium approach. Both the retaining wall and shear key were modelled as plate elements in PLAXIS 2D. The results of limit equilibrium analysis suggested that the use of a shear key enhances the stability of the retaining wall against sliding. The location of the shear key does not influence the stability of the retaining wall against sliding. It was also found that the increased depth of the shear key reduces the stability of the retaining wall against overturning, and the optimum location of the shear key is at the heel of the wall base. Results from the Finite Element Analysis show that the overall stability of the retaining wall increases with an increase in depth of the shear key. The point of rotation is assumed to be located underneath the toe of the wall and at a depth of the shear key. From the Finite Element Analysis, changes in the direction of displacement were visible around the assumed location of the point of rotation for all three locations of the shear key. Hence, the assumed location of the point of rotation is reasonable in this study.
item: Conference-Abstract
Establishment of soil water characteristic curves for Sri Lankan residual soils
(Department of Civil Engineering, University of Moratuwa, 2021-11) Ranasingha, RHATD; Kulathilaka, SAS; Hettiarachchi, P
The water content in an unsaturated soil is a function of the suction present in the soil. This relation between soil water content and suction could be represented by the soil-water characteristic curve, which is a plot of volumetric water content vs suction. SWCC is a fundamental characteristic for forecasting other soil characteristics such as permeability characteristics and unsaturated shear strength of the soil. As a result, SWCC plays an important role in identifying the engineering characteristics of a soil. Rain induced slope failures are a major challenge faced by Sri Lankan Geotechnical Engineers. As most of the slopes in Sri Lanka are formed by residual soils, establishment of Soil Water Characteristic Curve - SWCC for Sri Lankan Residual soils is very useful in predicting rain induced slope failures. Soil Water Characteristic Curve (SWCC) is necessary to model the loss of matric suction caused by rainfall infiltration into a soil. Pressure plate apparatus method and Method of continuous measurement are two methods used to derive the curve experimentally. These methods are accurate but time consuming and expensive. There are also empirical methods of deriving SWCC using particle size distribution and plasticity limits. However, to gain confidence in using them, results obtained by the two techniques should be compared. In this research study, empirical methods by Arya & Paris (1981), Zapata (1999), Fredlund & Xing (1994) and Van Genuchten (1980) are compared with experimental methods. Series of tests were done on different types of Sri Lankan Soils. Manufactured sand (Fine) and a lateritic soil were used in this research. Manufactured sand obtained from crushing of rock and rock particles were sieved through 0.425mm size sieve to obtain the test samples and Lateritic Soil was sieved through 10mm size sieve. According to results obtained from this research study SWCC obtained for Manufactured sand using Van Genuchet, Zapata and Fredlund and Xing methods are in close agreement with the results obtained experimentally from the method of continuous measurements. The air entry value for the soil is nearly 7-8 kPa. For Lateritic soil, Van Genuchet and Fredlund and Xing models are in close agreement with the results obtained experimentally from the method of continuous measurements. The average air entry value is nearly 25-30 kPa. After comparing the results, it could be concluded that the most reliable and appropriate empirical methods to derive the SWCC empirically are Van Genuchet and Fredlund and Xing models. Fredlund and Xing model is more useful as it can be incorporated with SEEP/W software in modelling of permeability curve.
item: Conference-Abstract
Feasibility of using pre-stressed concrete over conventional reinforced concrete in water retaining structures
(Department of Civil Engineering, University of Moratuwa, 2021-11) Madhushani, WLAC; Hidallana-Gamage, HD; Jayamangala, HAC; Hettiarachchi, P
Water is considered the source of living for every creation, as it is a crucial element for healthy living. A Safe and adequate supply of potable water is one of the basic elements for the human to sustain a healthy life. Concrete is generally the most common material of construction of water tanks and when correctly designed and constructed, will provide long life and low maintenance cost. It is important to carry out both the design and construction of water retaining structures properly, otherwise, it would not give the intended service. Water tanks must be designed so that liquid is not allowed to leak or percolate through the concrete structure during the life of the structure. With the rapid speed of urbanization, demand for drinking water has increased by many folds. Also, as demand for water tanks will continue to increase in the coming years, quick construction methods and the most economical method will be helpful in the selection of tanks for real design. PC is the best solution for that. In this paper, design guidance for PC circular water tanks resting on the ground is presented. Both reinforced concrete (RC) and prestressed concrete (PC) alternatives are compared considering the total cost of the tank. The design and construction approaches for PC circular water tanks were identified following BS 8110-1: 1985 and BS 8007: 1987. The finite element software model of each tank was developed separately and each of the circular water tanks was analysed using Midas Gen software. The FEMbased design procedure developed in this research could be used to complement and supplement the existing design methodology for PC water retaining structures. The output of reinforced concrete designs and the output of post-tensioned concrete designs were converted into structural drawings and bills of quantities. Finally, both outputs were compared. Results of the material takeoffs showed that RC is economical only for 4000 m3 or less capacity. For higher capacities, a PC tank cost about12-14% less than the corresponding RC tank at prices prevailing in 2020. The paper helps in understanding the design philosophy for the safe and economic design of water tanks with better crack control.
item: Conference-Abstract
Framework for sustainable management and utilization of wetland resources: a case study of Madinnagoda marsh
(Department of Civil Engineering, University of Moratuwa, 2021-11) Pathirana, HA; Manathunga, JMA; Hettiarachchi, P
Wetlands, the lands of areas saturated with water throughout the year or seasonally, are the caretakers of the earth due to the reason that they provide an unparalleled range of environmental benefits. Wetlands actively contribute to making this world liveable. However, the sad truth is that wetland habitats continue to be lost entirely or progressively degraded at an alarming rate, regardless of the multitude of benefits that the wetlands provide. Wetlands are badly subjected to environmental pressures as a direct consequence of anthropogenic activities, which are the driving forces that lead to ecosystems damage. In turn, the state of such ecosystem changes subsequently impact the natural environment as well as the society. Madinnagoda wetland is one such valued ecosystem embracing the sad truth of wetland degradation that had occurred persistently during the past few decades. Close proximity to a highly urbanized area thus receiving a high value on its land extent, the severe shortage of land for economic development in the city, availability of a large extent of land in this wetland, and its location in the heart of Colombo make this wetland becoming a populated and rapidly developing area of Colombo District attracting more urban life. The exploitation of this wetland resource has vast negative consequences if this trend continues. Based on such concerns, issues of sustainability have been in focus lately, with Colombo’s wetlands declared as Ramsar sites. The necessity of a proper mechanism has arisen to maintain these ecosystems as they were. Therefore, this research was carried out to develop a framework for sustainable management and utilization of wetland resources at Madinnagoda Marsh. The DPSIR framework was used for the study, one of the best tools recognized to analyse environmental problems and devise sustainable solutions. However, it has been subjected to critiques in the literature. Although the confusion between the terminologies is identified as the main reason for such criticism, the framework has been subjected to many evolutions to give the best output. After analysing the Madinnagoda wetland with nested DAPSI(E1 and S1)R(M1) framework, a development plan was proposed, and its capability of sustainably managing and utilizing the wetland resources was measured as per the level to which its strategies fulfil the 17 Sustainable Development Goals. For this purpose, scorecards were developed under each weighted sustainable goal to assign the development plan with scores, and then, a methodology was developed to calculate the sustainability score. Finally, a wetland rating system was proposed to decide the level of sustainability of the Madinnagoda Marsh. Since there is no ongoing development plan for Madinnagoda Marsh targeting its sustainable development, this research study leaves the validation phase as a future work - though a hypothetical situation is proposed to ensure that the procedure and the validity of the framework that have been proposed is well demonstrated. Therefore, it is possible to modify the proposed development plan, proposed framework, and rating system to comply with the future settings aiming at achieving sustainable utilization of wetland resources. Even so, the beneficiaries of the wetland resources and the public at large should make sensible decisions to determine how they are going to sustainably manage and conserve this valued ecosystem.
item: Conference-Abstract
Improve the lateral stability of variable height steel truss type pedestrian bridges in Sri Lanka
(Department of Civil Engineering, University of Moratuwa, 2021-11) Liyanage, MLLN; Hidallana-Gamage, HD; Hettiarachchi, P
This paper investigates the methods of improving the lateral stability of variable height truss type steel bridges that are used for pedestrian purposes in Sri Lanka. A bridge is a structure that provides passage without blocking the way underneath over an obstacle. A truss is one of the key engineering features related with bridges in the emerging civil engineering contest. Several truss type steel bridges have been built for pedestrian use in the recent past. Modified Warren and variable height bridges can be commonly seen in the Southern Province of Sri Lanka over the major river crossings. When designing a pedestrian bridge for local conditions, it is very important to consider the loads due to pedestrians, wind, and sometimes light weight vehicles in the rural areas. So, it is preferred to investigate the applicable truss types and their shortcomings by conducting a detailed analysis. The aim of this research is to provide an overview of the Finite Element (FE) method with the focus on lateral stability of the variable height steel truss type pedestrian bridges, their analysis, and various applications. The applicability of steel hollow and composite sections to improve the lateral stability of steel truss type bridges were studied. A comprehensive literature review was carried out to identify the behaviour of different member sections under applied loads. FE analysis was performed using the SAP2000 software to investigate the behaviour of truss type steel bridges. The loads acting on the pedestrian bridges were calculated based on BS 5400: Part 2: 1978, where the design code BS5950: 2000 was used for the design of member sections. Later, MIDAS CIVIL software was used when analysing the truss bridges having concrete infilled composite sections for the top chord members by accounting for the buckling analysis. Span vs tonnage graphs were developed for the Variable Height Arch, Inverted Arch and other selected bridge types to investigate their steel usage for different spans. Almost all the bridges consume similar tonnage up to 25 m span, and their tonnages notably varied thereafter. Results from this study indicated that variable height bridges with concrete infilled sections consume less steel tonnage compared to those with hollow sections and other truss types. Furthermore, it was evident that the steel truss bridges with circular hollow sections consume slightly less steel tonnage compared to those with rectangular hollow sections for all the spans. This trend could be seen for both hollow and infilled sections. Overall, it can be concluded that the lateral stability of variable height bridges can be improved by using infilled sections, reducing their buckling effect, which is the main shortcoming of variable height steel truss type bridges.
item: Conference-Abstract
Improvement of compressibility characteristics of waste material by dynamic compaction
(Department of Civil Engineering, University of Moratuwa, 2021-11) Rathnayaka, RIA; Kulathilaka, SAS; Hettiarachchi, P
Open dumping is the most prevalent method of waste disposal in Sri Lanka. These sites, which are currently used as waste dump yards in urban areas, will have to be rehabilitated to be converted to be used as parks, roads or for other different construction projects. Establishing the strength and stiffness characteristics of these waste materials at different levels of degradation and how these characteristics can be enhanced to suit the proposed developments is a major challenge. The mechanisms of settlement that govern the solid waste material are numerous and complex. Bowders et al. (2001) reported that there are many reasons behind this behaviour of waste such as extreme heterogeneity of the wastes, their own particle deformability, the large voids present in the initial waste fill, and their biodegradability. According to Watts and Charles (1990) and Manassero et al. (1996), the settlement behaviour of MSW is often classified as occurring in several distinct phases. Primary consolidation of solid waste occurs due to the self-weight of the waste or application of surcharges such as fill over the time. Primary compression is then followed by the secondary compression. Secondary compression occurs due to biodegradation process in waste fill, and it can take years for this settlement to complete depending upon various phases of waste that it consists of. This paper presents a study of the effectiveness of dynamic compaction as a technique of enhancing the compressibility characteristics of waste dumps. MSW was subjected to dynamic compaction in a laboratory test setup, and another MSW sample was kept uncompacted. Next, MSW samples in both compacted as well as in non-compacted state were subjected to loading in a Rowe Cell of diameter 150 mm and height 50 mm and results were analysed to establish the compressibility characteristics, namely coefficient of volume compressibility (mv), compressibility index (Cc), coefficient of consolidation (Cv) and coefficient of secondary compression (Cα). Finally, results were compared to assess the effect of dynamic compaction on compressibility characteristics of MSW and the effectiveness of the process is compared with that of preloading. Compression index of MSW that was subjected to dynamic compaction was reduced to about 50% of the compression index of the non-compacted MSW. Recompression index values of noncompacted MSW values are less than about 10% of compression index values of non- compacted MSW samples. Similarly, results obtained for coefficient of volume compressibility shows greater reduction by preloading compared to dynamic compaction. Both preloading and dynamic compaction show significant effectiveness in reducing the coefficient of secondary consolidation. In conclusion, compressibility characteristics of MSW can be improved significantly using both preloading and dynamic compaction. According to results observed in this study preloading can be considered as the more effective method. However, depending on the composition and the degradation level of the MSW sample used these results can be changed. Considering the time, it takes to achieve the required compressibility reductions by preloading, dynamic compaction can be considered as another advantageous option.

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