CERS - 2022

Permanent URI for this collectionhttp://192.248.9.226/handle/123/19854

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item: Conference-Abstract
Adoption of precast hollow core panels for external walls of multi-storey buildings
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Subakaran, R; Jayasinghe, MTR; Herath, HMST; Mallikarachchi, C
Precast hollow core wall panels have gained popularity for their efficient use as load-bearing and non-load-bearing wall elements. ICC ACOTEC hollow core wall panels are manufactured locally and intended to be used as internal partition wall panels in multi-storey buildings. Partition walls in general are not load-bearing elements, thus they do not undergo significant deformations. This research study focuses on verifying the usability of such precast panels as external wall panels in multi-story buildings, where their load resistance is investigated under lateral wind loads and vertical deformations due to column shortening effects. In addition, using the shape optimisation technique in-built into ABAQUS/CAE advanced finite element software and parametric optimisation study, a better layout for the precast wall is also proposed and its performance is compared with the current standard layout under similar loading and boundary conditions. The numerical model was validated using experimental test results and the optimised panel has a 16% lower net volume than the original hollow panel. Meanwhile, the optimised panel did not show any reduction in strength properties and does not pose any challenges in manufacturing. Using shape-optimised panel sections, panel assemblies are simulated to investigate the panel assembly response under wind loads. Further, recommendations are given on the maximum number of wall panels that could be installed as a single assembly under different wind load intensities at various heights of multi-story buildings. Considering practical aspects, these recommendations are integrated with proposals on connection mechanisms between panel assemblies. Due to the nature of the scope of this research study, long-term effects such as creep and fatigue were not incorporated, and it is recommended to conduct experimental tests for the proposed panel assemblies before practical usage.
item: Conference-Abstract
Analysis of optimal expansion level of a single runway airport
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Siriwardena, KDSV; Perera, HLK; Mallikarachchi, C
Air travel is rapidly increasing all over the world and airport capacities are crucial when serving this growing demand. When it comes to airport capacities, whether it is passenger or freight, runway capacity is the key determining factor among many. At the same time, adding a runway to an existing airport is an expensive process from the design itself to obtaining approvals, construction and completion, compared to any other developments associated with an airport such as passenger areas and other service areas. However, despite the cost and other negative external factors involved, most airport authorities tend to make a bold decision to add another runway to the existing airport without looking at optimising existing and future operations. This seems to be the case for the Bandaranaike International Airport (BIA) which made plans to add a second new runway to accommodate future traffic. Therefore, the main aim of this research is to identify how to achieve the optimal expansion of a single-runway airport without adding a second runway. This is achieved by identifying critical parameters that affect the runway capacity and analysing ways to obtain the optimal capacity. Hence, the next appropriate solution to accommodate future traffic growth is to optimise current operations rather than physical expansion, due to drawbacks such as high capital costs, long implementation times, community opposition, and so on. After collecting the necessary data, an analysis was carried out to determine the current capacity and the utilisation of the runway in BIA. From the analysis, it was found that during a peak period more than 50% of the runway capacity is idling, meaning that it is been underutilised heavily at present. In other words, BIA can simply double the operations with the existing runway and now the question is whether BIA expects a growth more than this within the next 15-20 years. Beyond finding out the truly available runaway capacity there are ways to optimise runaway capacities. One such option would be to assist air crafts to evacuate from the runaway in the shortest possible time so that they can conduct the next operations. This was found to be the next largest bottleneck hindering runaway capacity and as a result implementation of highspeed exits have been considered in this study using the REDIM software. In addition, the best departure and arrival sequences were discovered using Python code to utilise the time more efficiently as Runway Occupancy Time (ROT) differs according to the aircraft category. It canbe concluded that the existing runway capacity can be further improved by optimising the current operations, as ROT was reduced by 10%.
item: Conference-Abstract
Analysis of the effect of wind on façade fire propagation through computational fluid dynamics modelling
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Gunarathne, GKUS; Rathnayaka, S; Weerasinghe, TGPL; Nanayakkara, SMA; Mallikarachchi, C
Façade fires are one of the most critical and increasingly frequent hazards in buildings. These fires pose a great risk to the building occupants. The Grenfell Tower fire, which happened in 2017, killing 72 people, is one of the deadliest façade fire incidents. Events like these emphasize the importance of studying the nature of façade fires. Façade fires can spread quickly through the full height of the building. Also, these fires can spread into nearby structures. Researchers have identified several factors that affect façade fire propagation. The main factors include façade material, cavities, geometry of the building, and wind. The focus of this study is the effect of wind on façade fire propagation. Building standards have set requirements to ensure the fire safety of façades. A large-scale façade fire test is one of the methods that building standards have used for this purpose. There are several large-scale façade fire test types in different countries, and the nature of these tests varies significantly from one another. One common theme in all those tests is that they do not consider the effect of wind. Therefore, even though the façades are designed according to the building standards, there is an unforeseen risk in fire situations when the wind is present. This study tries to address that limitation by numerically modelling a large-scale façade fire test and assessing the effect of wind. Fire Dynamic Simulator (FDS) was selected as the numerical tool. FDS is a Computational Fluid Dynamics (CFD) software for fire-driven fluid flows. First, a validation study was performed by numerically modelling a large-scale façade fire test that was conducted in a fire test facility in Melbourne. The experimental setup was 18 m tall, and thermocouples were placed at 10.5 m, 13.5 m and 16.5 m heights to record the temperatures. Wind speed and direction were measured at a height of 10 m. The test specimen consisted of two façade materials: an aluminium composite panel (ACP) with a combustible polyethylene core and a completely non-combustible profiled aluminium panel. The ACP panels consisted of a 4 mm polyethylene core sandwiched in between two 1 mm thick aluminium sheets. These materials were simulated in the numerical model using the material properties gathered from literature and product-specific data sheets. The total dimensions of the numerical domain were 22.4 m x 20.8 m x 19.2 m (length x width x height). This domain was large enough to account for the whole test, the fire plume resulting from the combustion, and the turbulences due to wind. Monin-Obukhov similarity theory was used to model the wind inside the numerical domain. The thermocouple results were extracted from the numerical model, and they were validated using the experimental results. The flame behaviour of the numerical model was compared with that of the experiment for further validation. After the validation, the effect of wind was examined through further numerical modelling. It has been shown that wind has a significant impact on façade fire propagation. The façade fire spread decreases with increasing wind speed when the wind direction is parallel to the main wall of the test specimen. Wind direction also impacts fire propagation. Findings from this study highlight the importance of considering wind in façade fire safety, especially in large-scale façade fire tests.
item: Conference-Abstract
Applicability of calcium carbide residue for soil stabilization: a systematic review and a meta-analysis
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Sandamali, DMTU; Sampath, KHSM; Mallikarachchi, C
The use of Calcium Carbide Residue (CCR) which is a calcium-rich material as a soil stabilizer is often discussed as a solution to reduce negative environmental impacts and costs involved with soil stabilization with cement. By mixing an optimum CCR content with soil, a significant improvement can be achieved in soil properties. In terms of compaction properties, the addition of CCR decreases the maximum dry density (MDD) of soils while increasing the optimum moisture content (OMC). A significant increment of unconfined compressive strength (UCS) is observed with the increment of CCR dosage. However, the UCS of stabilized soils tends to decrease with further addition of CCR once the optimum CCR content is reached. In addition, the plasticity index (PI) of natural soils decreases with the addition of CCR and becomes constant after the optimum CCR content is reached. This particular research studies the applicability of CCR as a soil stabilizer with a comprehensive literature review and several statistical models and correlations were developed to be used in the pre-feasibility stage of applying CCR as a soil stabilizer. Prediction models were trained and validated by analyzing the data collected from similar studies using the statistical tools available in Excel and MATLAB software. This study describes a multivariate linear regression model and a multivariate polynomial regression model which can predict the MDD, and OMC of soils stabilized with CCR, respectively within a prediction accuracy of ±5% using the compaction properties of natural soil and CCR mix proportion. Also, an artificial neural network (ANN) model with a R2 value of 0.99958 and an accuracy range of ±16% was developed to predict the UCS of CCR-stabilized soil after a curing period of 28 days. In addition to that, a gaussian process regression (GPR) model was introduced to predict the plasticity index (PI) of CCR stabilized soil with a R2 value of 0.98 and a predictive accuracy of ±3%. This model can also be used to estimate the optimum CCR content.
item: Conference-Abstract
Applicability of standard density in quality control and quality acceptance of asphalt surfacing
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Rathnasiri, KAPS; Mamperachchi, WK; Mallikarachchi, C
Proper compaction plays a vital role in maintaining the quality of asphalt pavement works. As a quality control (QC) and quality acceptance (QA) parameter, the degree of compaction expressed as a percentage ratio between field density and the reference density is employed in the pavement industry. Currently, Marshall density, maximum density and control strip density are used to establish the reference density and formulate the degree of compaction. However, for decades, Marshall laboratory density has been the mainstream practice to specify the reference density in Sri Lanka. This study focuses on developing a systematic approach called the "Standard density method" to establish the reference density. The standard density is determined as the mean value of densities of Marshall test specimens from morning and evening operations for a specified number of days after the commencement of construction. The experiments were designed to evaluate the feasibility of the concept of standard density by comparing current practices with the proposed method. Field core density and Marshall laboratory density measurements were collected from various road projects, and compaction performances were evaluated. A graphical comparison, a statistical test method (t -test) and validation tests were conducted to analyze the compaction performance and acceptance of the proposed method. The findings showed that standard reference density could be used as the most effective QC / QA testing parameter for roads that use the same asphalt mixture design, batching plant, laying and compaction procedures. Moreover, statistics revealed a significant relationship between the level of compaction results in both current and proposed methods in major projects. Furthermore, the results showed that the standard density method is very sensitive to the variations in asphalt manufacturing, placing, laying and compaction procedures.
item: Conference-Abstract
Assessment of traditional water yield forecasting methods based on selected two dry zone basins in Sri Lanka
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Madusanka, WDP; Rajapakse, RLHL; Mallikarachchi, C
The majority of dry zone basins are still ungauged in Sri Lanka, and this has led to uncertainties in the planning and development of water management infrastructure. The Irrigation Guideline of Sri Lanka (IGM) has been widely in use to estimate the basin yield, but even so, there is insufficient evidence to evaluate the accuracy of the estimations under the changing climate conditions. Therefore a need exists for the comparison of available water yield models to close this gap and provide accurate yield estimations. In the current study, the observed streamflow yield data from Kirindi Oya and Maduru Oya basins were used to compare the yield estimates derived from the IGM and HEC-HMS models. Daily and 75% probable rainfall data were considered as the input data for the models and the model results were compared with the observed streamflow data. The evaluation has been carried out by considering the flow hydrographs, annual cumulative error, flow duration curves, runoff coefficients, and the Mean Ratio of Absolute Error (MRAE) value as an indicator. The two dry zone basins Thanamalwila and Padiyathalawa were considered for the study. The periods of comparison of the Thanamalwila and Padiyathalawa watersheds were from 2000-2015 and 2007-2015, respectively. Cumulative water yield error between observed and simulated yield, flow duration curves, and runoff coefficients were the critical elements used to compare simulation results with observations. Comparisons in the two selected basins show that the IGM is still the better model for estimating yield in watersheds in the dry zone, and it was found that rainfall is the dominant factor influencing yield. The comparison of the two models by using the 75% probable rainfall data as indicated in the IGM (Analysis 1) as the input data showed that it is the closest monthly yield evaluation model compared to observed data in the Padiyathalawa and Thanamalwila watersheds and annual differences in estimations were 47.9% and 39.8%, respectively. The HEC-HMS model results ended up with 83.9% and 83.8% annual differences for Padiyathalawa and Thanamalwila watersheds, respectively. In the comparison of the two models by using the actual rainfall data collected from the selected gauging stations (Analysis 2), for the Padiyathalawa watershed, HEC-HMS gives the closest monthly yield estimation with a 34.18% annual streamflow overestimation error. For the Thanamalwila watershed, the IGM model gives the closest monthly yield estimation, and the annual error was 32.2%. The HEC-HMS model gives overestimated values in the Padiyathalawa watershed in Analysis 2 while producing underestimated values in other cases. The IGM produces underestimated values for all cases. Due to the ambiguous variation of HECHMS yield results in each watershed in the same zone, it is recommended that the IGM model be used for yield estimations in the dry zone basins with similar characteristics.
item: Conference-Abstract
Cost economics of precast walling systems for multistorey buildings – a case study-based approach
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Rathnayake, RMBCK; Jayasinghe, C; Mallikarachchi, C
Traditional monolithic building construction is labour and time- intensive and usually found in inadequate quality. Rapid urbanization and steadily expanding metropolitan populations need fast and time-saving construction technology, which can be aided using precast construction techniques. Precast construction offers numerous benefits including reduced construction time, minimal labour requirement, less resource wastage and higher quality. Despite the advantages of precast construction technology, Sri Lankan multi-storey building construction still predominantly relies on conventional on-site construction techniques due to a lack of fresh knowledge and less awareness about the benefits. Hence, this study aims to assess the cost- effectiveness and environmental impact of adopting precast concrete walling systems in multi- storey building construction in the Sri Lankan context through a life cycle thinking approach. This paper compares a precast concrete walling system with a conventional Cement Sand Block (CSB) walling system in terms of Life Cycle Cost (LCC) and Life Cycle Assessment (LCA). It evaluates the total impact using Eco-Efficiency Analysis. A case studybased approach was adopted and the LCC was compared using the Net Present Value (NPV) method. The results show that the CSB walling system is more cost-effective than the precast concrete walling system in the long run in the Sri Lankan context. But the Ecoefficiency Index of both walling materials is in the same range according to the percentages they got. Moreover, precast walling system shows considerable time and labour saving with improved quality of construction. Therefore, the findings of this study help to select a walling material for multi-storey building construction from a broader perspective.
item: Conference-Abstract
Design optimisation of a steel bridge bracket
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Liyanagunawardhana, SK; Herath, HMST; Mallikarachchi, C
Steel brackets have a renowned potential of being used in bridge constructions as a load-bearing element. Due to the higher consumption of steel in bridge constructions, the emission of Carbon Dioxide (CO2) gas is increased when manufacturing steel components. CO2 is one of the main greenhouse gases prompting the increase in global warming. Moreover, excessive material usage in bracket manufacturing will lead to expensive constructions and increased embodied energy consumption. Another concern is that, though the material usage is to be reduced, the strength, stiffness and stability of the structure should be preserved. Hence, engineers have identified that structural optimisation is the best solution to address this global problem, and they have been practising structural optimisation principles on the structural components recently to achieve sustainability during the service life. In other words, their ultimate target is to apply sustainable concepts to the construction principles. Although many researchers have studied various structural optimisation tools and presented novel designs, applications of those designs in the construction industry are still limited due to the complex geometries of the optimised designs. Nevertheless, the advantages of optimised designs are more powerful than the manufacturing challenges. The recent developments in additive manufacturing extend higher flexibility and efficiency to the fabrication of these structures by overcoming the manufacturing challenges. However. nowadays, these novel and eco-friendly techniques are getting more attention all over the world because of their merits in the ever-evolving field of Civil Engineering. To circumvent the above-mentioned challenges, this research demonstrates a novel approach for producing an optimum and sustainable steel bracket for a pedestrian bridge construction. Among several structural optimisation methods, topology optimisation is used as the tool of choice in this work, which has a proven record of arriving at the highest stiffness to weight ratio. This study uses an existing steel bridge bracket in Castleford Foot Bridge, England as a study case. The bracket is optimised under several volume fractions and ultimately, the optimum design is selected based on both simulation results and practical considerations. According to the results, the optimised model with a 30% volume constraint is selected as the optimum design which leads to the manufacturing of cost-effective and sustainable structure. Considering the manufacturing possibilities, the optimised model from the finite element software is converted into a manufacturable parametric Computer-Aided Design (CAD) model using the Rhinoceros software package for further post-processing and analysis. The modified CAD model is re-analysed using finite element software and its structural performance is verified. It is shown that a considerable amount of material could be saved without sacrificing the strength and stiffness requirement of the bridge bracket. Similarly, further optimisation could be performed in terms of the shape of the geometry which is identified as a potential future work that stems from this study.
item: Conference-Abstract
Design-informed structural optimisation
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Amarasinghe, IT; Herath, HMST; Mallikarachchi, HMYC; Mallikarachchi, C
Structural optimisation has become an important tool in the field of Civil Engineering, but there is limited research done on structural optimisation of specific structures and components, especially for large construction machinery. By optimising construction machinery components, it is possible to reduce the material usage and decrease the cost of the machine, without compromising its strength. This research study looks at a case study of optimising a wheel loader arm. Initially, the critical load calculation and the static force analysis of the wheel loader arm were conducted and the forces and reactions acting on the arm were obtained. Then a finite element analysis was conducted by assigning the relevant loads and boundary conditions and the results obtained deemed that the stresses and displacements of the arm were within the acceptable limits. The Solid Isotropic Microstructure with Penalisation (SIMP) for intermediate densities method is used for the topology optimisation process considering the minimum compliance as the objective function and the volume fraction as the constraint. Using the Abaqus FEA software, topology optimisation models were obtained for different volume fractions and the most optimum geometry comparing maximum von Mises stress, displacement, and mass with the original design. After the completion of the topology optimisation process, Computer-Aided Design models are generated by exporting the mesh into SOLIDWORKS. Subsequently, shape optimisation is conducted considering the different manufacturing constraints. The final optimised model has a 20.3% reduction of mass compared to the original structure, while stresses, displacement and strains are kept within the allowable limits in accordance with codes of practice. This case study demonstrates on how structural optimisation can be integrated into the designs of different structures and components. By using a similar method, it is possible to optimise different components of the wheel loader arm and other construction machinery components. These optimisations will reduce the weight and material usage of these components, which can help reduce the overall cost of the machines significantly.
item: Conference-Abstract
Development of an overall construction productivity assessment framework and an improvement model
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Premakumara, UAK; Siriwardana, CSA; Mallikarachchi, C
The construction sector is one of the most vital industries in a nation as it directly assesses the populace's necessities. Globally, the construction industry is among the top five trades, contributing significantly to the national Gross Domestic Product (GDP) yet due to its complexity and high frequency of unanticipated occurrences, the sector relies on labour input more than any other major contributor to the national GDP. Further, the assessments on construction productivity were found to be regionalised, making them inapplicable to local or distinct settings. In response to the aforementioned factors, the current study has established a unique evaluation of the context of construction productivity based on a global systematic examination of 130 distinct studies, dividing the world into 9 distinguishable regions of, 1. Australia-New Zealand Region; 2. North American Region; and 3. Eastern Asian/Russian Region. 4. Middle East Region, 5. European Region, 6. Southeast Asian Region, 7. South Asian Region, 8. South American Region, and 9. African Region. Consequently, a set of productivity benchmarks has been constructed from the same literature to analyse 915 various characteristics that contribute to a lack of construction productivity in the worldwide context into the 50 most prominent aspects, as determined by the above systematic analysis. The scrutiny was conducted using a framework based on the concepts of Pareto Analysis and Frequency Analysis, where factors were assigned in accordance with the scope of each benchmark, based on Pareto Analysis, and the most prominent characteristics of each factor under the benchmark were enumerated using the frequency approach. Accordingly, the results have been tailored for the Sri Lankan context through a cross-sectional survey of 117 stakeholders, ranging from executive project managers to labourers, culminating in a ranking of the most prevalent criteria for the Sri Lankan context. Using Pareto and Fuzzy Analysis techniques, the study has successfully mitigated the most crucial component in evaluating construction productivity in a global construction context, namely the subjectivity of evaluation, while also taking into account the interdependence of benchmarks through the utilisation of dedicated Fuzzy Analyses and Interdependence Assessment Frameworks, respectively. As the study's final deliverable, the 20 most prevalent factors were considered, and a measuring methodology of productivity and improvement model for each was introduced based on case studies and literature available on each aspect (137 Studies), allowing users or practitioners to adapt and improve productivity at the corresponding venues, achieving the study's ultimate goal of developing a globally adaptive, overall construction productivity assessment framework and an improvement model for the Sri Lankan Construction Context.
item: Conference-Abstract
Development of economical driving cycle for motorcycle and emission estimation
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Wijekoon, MDPLP; Perera, HLK; Mallikarachchi, C
In developing countries like Sri Lanka, motorcycles (MC) are a popular mode of transportation due to their economic implications. This study looks at how an MC operates under various traffic conditions in Sri Lanka and the content of combustion gases emitted to propose emission policies. For this purpose, the driving cycle for the motorcycle was first developed. A Driving Cycle (DC) is a speed-time profile, and it represents the driving characteristics of a selected region. DCs are widely used to estimate transport air pollutants and for building emission inventories. Thus, knowledge of the driving cycle is essential for the evaluation of exhaust emissions. DCs can be used for different purposes such as setting up the emission standards, determining the behaviour of the driver, the traffic condition of the selected route, determining the travel time, and for traffic management purposes. As driving cycles are dependent on the driver's behaviour, mode of transportation, traffic condition, and road conditions factors, existing driving cycles developed for other vehicle types in Sri Lanka or developed for MCs in other countries cannot be used in Sri Lanka because they are different due to above said reasons. One of the main objectives of this study is the development of a driving cycle for motorcycles. For this study, the most popular types of motorcycles ranging from 100cc to 150cc engine capacities were used. Motorcycles with these engine capacities were more suitable for this study as they are widely used in major cities as well as sub-major cities of the country. For this study, driving data is collected by motorcycle riders who are frequently riding the motorcycle in urban and suburban areas using a handheld GPS device. During the data collection, special attention is paid to the peak times because the traffic is significantly higher during such times and thus, the amount of combustion gases emitted is also high. This GPS-based data collection is more economical than other methods of collecting data for the driving cycle development. The collected data was filtered and the unusual characteristics were removed by using a Python code and after that data was divided into micro trips including idle time. Micro trip-based cycle development is suitable for developing a driving cycle to estimate emissions. The micro trips thus created are randomly attached to create several candidates DCs. From those DCs, the best representing DC is selected by comparing the Speed Acceleration Frequency Distribution (SAFD) graph. The final DC selected has an average speed of 27.26 km/h, an average running speed of 35.31 km/h, an average acceleration of 0.284 ms-2 and an average decelerate of 0.2846ms-2. Since there are no facilities in Sri Lanka to run the DC developed on a chassis dynamometer to measure the respective emissions, an approximate method was used in this study by referring to similar studies carried out elsewhere. Based on such comparison, the proposed emission factors for motorcycles are CO 0.5-3.0 g/km, NOx 0.2-0.4 g/km and HC 0.25-0.4 g/km for Sri Lankan conditions. These threshold values are suitable to set up new emission standards for MCs in Sri Lanka or in other words setting up local emission goals and adopting a carbon tax for MCs. On the other hand, these policies may encourage users to invest in low-carbon transport modes. It can save fuel by performing periodic emission tests for motorcycles and removing or restoring the engines. It helps to minimise fuel and energy wastage.
item: Conference-Abstract
The effectiveness of different structural forms for mediumrise apartment buildings
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Wijekoon, KMSR; Jayasinghe, MTR; Herath, HMST; Mallikarachchi, C
To fulfil the housing requirements of the ever-growing population with the scarcity of valuable land, the best solution is to come up with high-rise or medium-rise apartment buildings. The effect of lateral forces (wind and seismic) on those structures is significant to be studied because they govern the structural design. The selected structural system should be optimal in the aspects of associated cost, structural efficiency and maximum usable floor area. Therefore, once the structural form of the lateral load-resisting system of a building is defined, the optimal element sizes should be derived while satisfying all serviceability lateral stiffness and practical sizing requirements. This comparative study evaluates the effectiveness of six different structural forms of 20-story RC (Reinforced Concrete) structures under the effect of wind and seismic loadings including a moment-resisting frame as the base model, four wall frame structures, and a frame-tube structure. Maximum top story displacement, inter-story drift ratios, member forces and moments utilisation, associated cost, and human perception level for windinduced lateral acceleration were considered as the parameters to carry out the comparison. The main objectives of this study are to assess and compare the wind-induced lateral behaviours and behaviours against earthquake loadings of rigid-frame,wall-frame, and frame-tube medium-rise structures and to determine the most effective structural system for medium-rise apartment buildings based on established parameters. The methodology which was followed, 1. Establish the parameters/ design criteria that need to be satisfied. 2. Study the wind load and seismic load effect on typical medium-rise structures. 3. Select six different structural forms including a moment-resisting frame as the base model, four wall frame structures, and a frame-tube structure for the case study. 4. Develop FEM models and do the comparison based on established parameters. 5. Optimisation and cost analysis. The major findings can be identified as followings. The lateral stiffness of bare frame structures can be increased considerably by increasing the depth of beams rather than increasing the size of columns. As well as in bare frame structures, the columns which are in line with the shear walls along the windward direction are subjected to high axial forces when the structure is subjected to wind effects. Also, with the addition of a sufficient amount of shear walls at lucrative positions, the required axial forces and bending moment capacities in both columns and beams can be reduced drastically. Even though the frame-tube structure shows better performances in lateral stiffness, the columns and beams are subjected to high axial forces and bending moments because the overall lateral stiffness is provided by columns and beamcolumn rigid joints.
item: Conference-Abstract
Establishment of threshold rainfall intensities for critical slopes in Sri Lanka
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Panagoda, VR; Panagoda, SAS; Mallikarachchi, C
All the landslides in Sri Lanka are triggered by excessive rainfall. Sloping grounds in Sri Lanka are formed of; residual soils, rocks at different levels of weathering and colluvial soils. During periods of dry weather, the groundwater table is low and prevailing matric suctions will ensure stability. With rainwater infiltration, matric suction will be reduced or lost, and perched water table conditions may occur developing instability. Susceptibility to landslide in hilly terrain was assessed by National Building Research Organization considering six terrain factors, and four levels of susceptibility were established. The threshold rainfall values triggering failure in these four regions would be different. Hence, they should be obtained by proper modelling of rainfall infiltration and the subsequent reduction of safety factors. In the absence of such an analysis, threshold values based on experience are currently used in issuing warnings. The process should be improved by identifying site-specific threshold values. In this research, initially, a parametric study was conducted by applying different rainfall intensities for a typical high slope of uniform residual soil layer and a layer of residual soil overlying a weathered rock using GeoStudio 2018. The threshold values were obtained under different initial conditions (cohesion and matric suction). A strong correlation (R2 ~ 0.9) between rainfall intensities and duration of instability was observed in all cases. Hence, if the rainfall intensity of a particular event is known, the time taken for instability can be estimated. It will be important to take remedial measures and make decisions on early warning more reliable. Also, the identified dependence of threshold values on the initial conditions highlighted the importance of establishing site-specific threshold values. The study was then extended to three actual landslides: Pinnawala, Badulusirigama and Ginigathhena. The rainfall records that triggered the landslide at Pinnawala were available. Hence, the failure event was back analyzed using the subsoil conditions that were established subsequently during the rectification stage. As Badulusirigama and Ginigathhena slopes were recently rectified, the threshold intensities were studied separately for the situation before and after the rectification. A clear indication of an increase in threshold rainfall values was established. Hence, these slopes would be able to withstand intense rainfalls that may fall due to climate changes. However, any records of the rainfall events that caused failure at the two locations were not available for any back analysis. The slopes with varied rectification techniques reveal that subsurface drains, which lower the water table and partially desaturate the topsoil, more efficiently increase stability than surface drains. The surface drains are only effective while raining to facilitate runoff before infiltration.
item: Conference-Abstract
Flood forecasting in selected wet zone basins using probabilistic rainfall thresholds
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Ganegoda, GPYR; Rajapakse, RLHL; Mallikarachchi, C
Rainfall threshold studies have been carried out in Sri Lanka, yet only to forecast landslides and it has the benefits of not requiring either real-time modelling or real-time runoff data while having the ability to forecast flash floods with significant lead time when combined with the weather forecasts. Previous flood forecasting studies of the rainfall threshold method have been carried out using various hydrological models and techniques based on the background but all commonly followed basic hydrological modelling, generating rainfall patterns/events with subsequent model runs with generated hyetographs. The selected study regions for the present study are the Baddegama and Ellagawa watersheds which are located in the wet zone of Sri Lanka. Rainfall Runoff Inundation Model (RRI) was selected as the hydrological model since it has been widely used in flood-related research and the input/output files of the RRI model are easily readable and interpretable. A Python script was compiled to generate random rainfall patterns and find the Thiessen averaged cumulative rainfall threshold which led to a two-year return interval flood from each pattern with RRI. A large number of random events with increments of 25 mm rainfall were run until they caused the threshold discharge which was considered as the two-year return period discharge based on past data. From the results, Ellagawa watershed is found to be safe from a two-year return period discharge (778 m3s- 1) up to average cumulative 6-day rainfall of 225 mm and it can be guaranteed that 400 mm from a 6-day storm event will definitely cause flooding. Within the 225 mm and 400 mm range, there is a partial risk. For the Baddegama watershed, those lower and upper bound values were 250 mm and 550 mm for 5-day duration rainfall to cause a two- year return period discharge of 340 m3s-1. Rainfall threshold and their cumulative risk probability were plotted by sorting selected results from iterations. Considering the Probability of the Detention (POD) of the previous flood events with derived threshold limits and aid of the past data, the lower limit of the rainfall threshold range for the Ellagawa watershed shows a POD of 100% which means all events would be predicted by the lower limit but it was 87% for Baddegama. Rainfall thresholds representing 50 % of the risk percentages show POD values of 53% and 47% for Ellagawa and Baddegama, respectively.
item: Conference-Abstract
Fly ash-based geopolymer for well cement during co2 sequestration: an analytical study
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Sathsarani, HBS; Sampath, KHSM; Mallikarachchi, C
Generally, Ordinary Portland Cement (OPC) is used as a well cement during the CO2 sequestration process; however, it shows adverse failures in a CO2-rich environment and loses its isolation properties in a short time. Based on the previous findings on OPC-based gas well cement, its uncertainty in providing effective well integrity is revealed. Therefore, studying a novel well cement is one of the main requirements to conduct a sustainable CO2 sequestration process. Among them, fly ash (FA)-based geopolymer has a higher prominence due to the ability to reduce the gigantic amounts of fly ash piled up due to coal-fired power plant operations. The compressive strength and CO2 permeability of well cement play major roles in downhole conditions to maintain the wellbore integrity at different temperature and pressure variations. This study was carried out to develop predictive models for compressive strength and permeability of FA-based geopolymer cement using different independent variables. For this purpose, databases were developed to collect data from many laboratory studies available in the literature. Two models were developed for predicting 7 days of compressive strength of well cement using linear and nonlinear multivariable regression (MVR) analyses and Artificial Neural Network (ANN), and they were validated using the experimental data. One of the models developed using Si/Al ratio and curing temperature as independent variables have shown a good prediction accuracy with R2 values of 0.9332 for training data and 0.9761 for validating data. In the case of developing prediction models for CO2 permeability, five equations were developed under selected confining pressures using injection pressure and the curing temperature as independent variables. Coefficient of determination values (R2) of 0.880, 0.955, 0.959, 0.964, and 0.980 were obtained for each trained data in categorised subgroups under confining pressure values of 12, 16, 20, 25, and 35 MPa respectively for these developed equations.
item: Conference-Abstract
Framework to determine level crossing grade separation requirement
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022) Amarathunga, AADRD; Pasindu, HR; Mallikarachchi, C
Railway level crossings are a major consideration that road agencies often need to pay attention to when managing the issues related to safety, traffic, and land use in the road segment where it is located. Alternatives to avoid these issues include crossing consolidation, closure, improving the conditions of the existing level crossing, and grade separation. Grade separation is the ideal alternative since it completely separates the road and rail traffic, but it carries itself a downside due to the high project cost and maintenance, making it impossible to grade separate all the level crossings. Ineffective allocation of funds for a single grade separating structure could restrict the funds available for other development projects. With the increasing number of road users and the higher demand for the railway, increased congestion is more than certain without proper improvements to the network. To address this, frameworks have been proposed in many countries on how to identify and prioritise potential level crossings for grade separations, leading to effectively utilising the funds allocated. A knowledge gap was identified in the Sri Lankan context where the lack of a guiding framework leads to ad hoc decision-making and inefficient allocation of funds. This study aims to develop a criterion that can be used to identify the grade separation requirement in a Sri Lankan urban context. A number of existing studies were reviewed from which, different methodologies, key parameters and a limiting criterion for Average Daily Traffic (ADT) were identified. An economic analysis was then carried out to check the suitability of the limiting criterion for the local urban context. Two existing flyovers were selected representing four-lane and two-lane grade separations. Estimation of delay at the level crossings was done with VISSIM microsimulation software for different ADT levels. Savings from travel time, vehicle operating, and emission costs due to grade separating the level crossing were considered as the economic benefits. Estimated benefits were compared with the project cost and the maintenance cost of the grade separation. The project Benefit-Cost Ratio was then calculated for the previously considered ADT levels, and a sensitivity analysis was carried out considering different cases of changing benefits and costs to assess the economic strength of the selected criterion. Based on the above results, limiting ADT values of 90000 veh/day for four-lane level crossings and 45000 veh/day for two-lane level crossings, are recommended to identify the grade separation requirement.
item: Conference-Abstract
Homogenisation of ultra-thin woven fibre composite structures under high curvatures
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Weerasinghe, WUD; Herath, HMST; Mallikarachchi, HMYC; Mallikarachchi, C
Utilising fibre-based textile structure as the composite reinforcement results in making composite more tailorable and effective for applications where various types of loads are anticipated to be supported by the structure. Owing to that, growing demand for ultra-thin woven composites can be identified in weight-sensitive applications, especially in space engineering applications such as self-deployable structures. Both complex geometry and nonlinear behaviour of constituents of these composites make it more difficult to forecast the overall mechanical behaviour. Multiscale modeling approach can be identified as a popular strategy to overcome this issue where several models at various scales are utilised simultaneously to describe the system. For woven fibre composites, considered scales are micromechanical, meso-mechanical and macro-mechanical scales. Physical experiments revealed in the literature that these ultra-thin structures have experienced a significant drop in bending stiffness when subjected to extreme curvatures. This is a numerical study in meso-mechanical scale on the homogenised response of two-ply plain woven carbon fibre composites considering the inter-connection behaviour between contact surfaces within the ply and in between two plies. With dry fiber geometry and resin pocket introduced geometry, two distinct models were used in the analysis. To estimate the behaviour under higher curvatures, the study has been advanced further into the non-linear regime. Due to the severe curvatures that these ultra-thin woven composites are subjected to, slippage behaviour between yarns and between plies may take place, which would result in a drop in bending stiffness at those higher curvatures. Surface based cohesive constraints were defined to simulate the slipping behaviour using linear elastic traction-separation stiffness values. The dry fibre model captured the bending stiffness and Poisson’s ratio with good accuracy while the resin model captured the shear response better than the dry fibre model. Axial stiffness predictions remained almost the same for both cases. It is demonstrated that the proposed models can accurately predict the nonlinear flexural behaviour based on the experimental findings. Both models have shown their ability to accurately capture the bending stiffness reduction up to a curvature value of 0.14mm-1 and the stiffness reduction was overpredicted beyond that point. Reason behind the overprediction can be the allowance of relative moment between plies which can lead to the loss of compatibility between two plies and hence, each lamina contributes separately to the second moment of area instead of full thickness. Further development of resin model to capture both in-plane and out of plane properties in a single model can be recommended for future studies and also the effect of relative movement of plies to the second moment of area of laminate is recommended for further studies.
item: Conference-Abstract
Investigate the applicability of the fixed base and retaining wall type strctural arrangements in the construction of ground water reservoirs
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Aravinda, YAR; Gamage, HDH; Mallikarachchi, C
Ground water reservoirs are vastly used in water supply schemes for water storage. Both fixed base and retaining wall type structural arrangements are used in those without any basis, where mostly the selected arrangement will depend on the preference and the experience of the design engineer. The aim of this study is to develop a framework to select a proper structural arrangement for ground water reservoirs depending on the wall height and the capacity of the tank for an economical design with adequate structural capacity. Objectives of this research are analysing the ground water reservoirs with fixed base and retaining wall type base, designing structural components using available design standards and comparing results considering reservoir capacity and wall height. Most common rectangular shaped ground water reservoir capacities in Sri Lanka were studied. Finite Element Modelling (FEM) and theoretical analysis were used to study the structural behaviour of ground water reservoirs, and spread sheets were used to design structural components. Results obtained from this study were compared with an existing ground water reservoir. It was evident from the results that fixed base type arrangement is economical for all the wall heights of reservoirs having capacity up to 225 m3. For capacities between 225 m3 to 2000 m3, retaining wall type arrangement is economical for wall heights up to about 7 m, while fixed base type arrangement is economical for wall heights beyond 7 m. Overall, retaining wall type arrangement becomes economical for larger wall heights when the capacity increases. According to results presented in this paper, it is evident that selection of the base type (fixed base or the retaining wall type base) in a water retaining structure should be carefully done by considering the tank capacity and the wall height. Since this research was done for a length to width ratio of 1, further research should be done for different length to width ratios to check the validity of these conclusions. Further, this research was carried out using BS standards as the design practice. Therefore, this research can be extended using Eurocode to check the possibility of further optimisation of both structural arrangements.
item: Conference-Abstract
Microplastics detected in marine waters using spectroscopic analytical techniques: a review on the current state of knowledge
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Jayawardhana, H; Jayawardhana, WB; Mallikarachchi, C
Microplastics (MPs) contamination in marine waters has recently become a serious environmental concern. Hence, the identification of various types of MPs in marine waters is essential to control the MPs contamination in marine water. Several analytical methods have been adopted for the identification of MPs in marine waters and spectroscopic analyses are the most popular method adopted. In this study, a comprehensive review was carried out using published literature during 2010-2022 related to the identification of MPs in marine waters globally using spectroscopic methods. The present study is aimed at (1) identifying the most suitable spectroscopic method currently available to identify the MPs in marine waters, and (2) determining the most abundant type of MPs identified using the spectroscopic methods globally. About 65% of the reviewed studies (n=84) have adopted spectroscopic methods associated with the Fourier Transform Infrared (FTIR) and among them, 45% used the Attenuated Total Reflection FTIR (ATR-FTIR) method for the MPs identification in marine waters. By using the data available and comparing different aspects of the testing procedures of the reviewed studies (n=84) [cost of analysis, sensitivity, availability of the facilities], the ATR-FTIR method was found as the most suitable spectroscopic method to identify MPs in marine waters globally. Based on the data available from reviewed studies (n=31), Polyethylene (PE) (combined with LDPE and HDPE) was found as the most abundant type of MPs identified using spectroscopic methods globally. In conclusion, the present review provides insight into the applicability of the ATR-FTIR method for MPs identification in marine waters and the abundance of various types of MPs detected using spectroscopic methods.
item: Conference-Abstract
Modelling the spalling behaviour of concrete in fire
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) De Zoysa, RN; Dias, WPS; Weerasinghe, TGPL; Mallikarachchi, C
Spalling of concrete is a common phenomenon in reinforced concrete structures subjected to fire. As there are both macroscopic and microscopic factors involved, studying the behaviour of concrete spalling in fire is complicated. Permeability, pore pressures, moisture content, heating rate, and concrete type have been identified as contributing factors that influence concrete spalling in fire. Various experimental studies have been conducted to identify the behaviour of concrete spalling in fire. However, there is no exact method to determine spalling depth without conducting fire tests. Reduced cross-section and exposed reinforcement in a structural member due to spalling would significantly affect the overall stability of the structure. This research study presents a macroscopic finite element model to predict the spalling behaviour of concrete in a fire. The behaviour of concrete at elevated temperatures was modelled using the Concrete Damaged Plasticity (CDP) model, and temperature-induced transient creep strain in concrete is explicitly accounted for in the analysis, which is more representative of fire-exposed concrete structures. The finite element analysis program, ABAQUS, was used to model the reinforced concrete walls subjected to load and exposed to hydrocarbon fire. A nonlinear finite element analysis model for the rectangular concrete specimens was analysed using a sequential approach composed of a pure heat transfer analysis followed by a pure mechanical analysis. Thermal and mechanical responses of the model were validated using results obtained through fire tests conducted at the University of Melbourne. The developed finite element model was used to assess the effect of reinforcement concentration and clear cover on concrete spalling in a fire. Based on the results from the developed finite element model, it is evident that reinforced concrete with large cover thickness has a higher tendency to spall out in fire and also, cover to reinforcement has a major impact on the spalling of concrete. In addition, previous researchers have also experimentally identified that when the clear cover to reinforcement exceeds 40 mm, the spalling depth seems to have a greater tendency to become serious. It happens because the mass of concrete without support is significant. Other than that, it can be concluded that the concentration of reinforcement also has a minor impact on the spalling of concrete. Based on the above results, it is evident that densely reinforced concrete walls have a higher tendency to spall out in fire when the reinforcement spacing is less than 100 mm. It happens because of high thermal expansion and higher heat transfer rate through the structure. Further enhancements that can be used to improve the accuracy and reliability of the model are discussed.

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