CERS - 2022

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

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item: Conference-Abstract
Proceedings of the Civil Engineering Research Symposium - 2022 (Pre Text)
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Mallikarachchi, C
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
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
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
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
Study of the influence of construction sequence on slope rectification projects
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022) Kulathilaka, SAS; Vimukthi, HPJ; Mallikarachchi, C
Rain–induced slope failures in residual soil slopes are a common geotechnical hazard in most tropical countries like Sri Lanka. To reduce the risk of failure in slopes with low safety margins, or to rectify the slopes that have already failed, a wide range of risk mitigation measures are available. However, the application of such mitigation measures on a sloped body must be carefully planned, ensuring a sufficient safety margin exist, during the period of construction. Under this study, the importance of following a proper construction sequence for stability enhancement was studied using two rectification projects; one at Ginigathhena in Colombo – Hatton road and the other at Badulusirigama near Uva Wellassa University. The slope failure at Ginigathhena occurred with a toe excavation for the widening of the road, without realizing that it was a site of an ancient landslide. The rectification of the slope with the allowance for road widening was done later with; surface drainage, sub-surface drainage, and soil nailing. A top-down approach was adopted for the excavation. Initially, the water level in a flat waterlogged area at the upper part of the slope was lowered by surface drains and trench drains. The excavation of the slope was done incrementally from the top to down while installing soil nailing to support the excavation and installing the sub-horizontal drains to lower the groundwater table to economize the soil nailing design. The Badulusirigama project involved only surface and subsurface drainage without any change in the slope geometry. The failure mass consisted of three fully specified failure surfaces. During the rectification, the sub-horizontal drains were installed in a bottom-up approach. In this study, the importance of a correct construction sequence for stability enhancement was analysed using Spencer’s method. The analysis was done using GeoStudio 2018 software packages; SLOPE/ W and SEEP/ W. During the analysis for the Ginigathhena project, the stability condition of the failed slope before construction was evaluated under two case scenarios: with and without rainfall effect. The FoS of the slope without rainfall effect was found to be 1.105, but it has reduced to 0.947 during a rainfall event. So, before moving into more complex and time-consuming construction steps, the slope had to be stabilized to achieve a sufficient safety margin for the construction. As a result, the groundwater table lowering using upper slope surface drainage improvement and temporary sub drains were introduced to the slope. With the lowering of the groundwater table, the FoS has increased to 1.101, providing a safe environment to continue the further construction steps. The analysis indicated a FoS value lesser than one with the toe excavation. Therefore the excavation had to be conducted in a top-down sequence. But the initial excavation depth had to be minimized to a value of 6.8m and further excavation downwards had to be done along with soil nailing to support the unsupported excavation. For the Badulusirigama Slope rectification, the installation of sub-surface drains could be done in top-down, bottom-up, or intermediate sequences. But, the intermediate sequence was found to be most appropriate for the stability enhancement of all three failure surfaces promptly.
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
Utilisation of rice husk ash for soil stabilisation
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022) Ranathunga, RJKPN; Sampath, KHSM; Mallikarachchi, C
Rice husk ash (RHA) is one attractive additive that can be used for the enhancement of engineering properties of problematic soils as a full/partial replacement of cement/lime. The present study reviews the production of RHA and its basic characteristics as it relates to the performance of RHA-stabilized soils. For each soft ground improvement application, a substantial amount of time, money and effort is required for conducting extensive laboratory tests to evaluate the improvement of geotechnical properties of stabilized soil and identify the optimum mixture of additives. As an indirect approach, the present study explores the development of predictive models for geotechnical properties using multiple regression analysis (MRA) and artificial neural network (ANN) analysis. Laboratory experimental data sets from an extensive literature review were used to develop the models. The models for the prediction of Unconfined Compressive Strength (UCS), Soaked California Bearing Ratio (SCBR), Maximum Dry Density (MDD), Optimum Moisture Content (OMC), and Plasticity Index (PI) of RHA-stabilized clayey soil were proposed. It is noticed that at the prediction of S-CBR, and MDD, MRA gives better correlations with more than 95% prediction accuracy. Since MRA does not provide satisfactory performance for the prediction of UCS, OMC, and PI, ANN models were developed with R2 of more than 0.95. The proposed models were validated using the independent sets of data which is 30% of total data points. All the models express a good prediction capability with a prediction error of less than ±7.5%. A parametric analysis is performed to evaluate the variation of UCS of RHA-stabilized soil with the effect of influencing input parameters. The result of PA suggests that 6-12% of RHA in combination with a very little amount of cement (4-8%) or lime (3-6%) is the optimum mix proportion for RHA-stabilized soil ensuring the robustness and reliability of the proposed model. Hence, the proposed correlations may give easy access for facilitating the engineering decisions during the pre-feasibility assessment. Further research into the production process of RHA, the application potential of other waste materials to incorporate with RHA-cementlime binder mixtures and evaluation of indirect approaches to assess the characteristics of stabilized soil systems could lead to the utilization of RHA as a beneficial and productive alternative in soil stabilization.
item: Conference-Abstract
Study on climate elasticity of runoff in Kalu and Kelani river basins in the wet zone of Sri Lanka
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022) Wijekoon, WMRTY; Rajapakse, RLHL; Mallikarachchi, C
It is crucial to assess the impacts due to climate change on the hydrological cycle for the characterization of basin hydrology and water resource management. Climate elasticity can be used as an indicator to quantify the sensitivity of streamflow to climate change. This study estimates the climate elasticity of runoff concerning precipitation and evaporation, in the Kalu river and Kelani river basins in the wet zone of Sri Lanka. The Ellagawa subbasin of the Kalu river and the Hanwella subbasin of the Kelani river were selected for the assessment. The non- parametric estimator was selected based on the simplicity to assess the climate elasticity of runoff in the selected wet zone basins under current climate scenarios. At the same time, the climate elasticity under synthetic climate change scenarios was assessed using a hydrological model. The HEC-HMS rainfall-runoff model was selected based on the accessibility, flexibility, reliability, and data requirements to simulate streamflow. The rainfall elasticity and evaporation elasticity were estimated for prevailing climate conditions. According to the results, the increase in runoff due to the increase in precipitation under current climate scenarios is small compared to the reduction of runoff due to increased evaporation as a result of increased temperature, whereas according to the model results, climate change results in causing -41% to 31% change in runoff in the Kalu river basin and -49% to 23% change in runoff in the Kelani river basin based on two scenarios, respectively, under synthetic climate change scenarios that were developed for the period of 2016-2035 considering the predicted precipitation and evaporation changes comparative to the baseline period of 1986-2005. According to the results, these crucial river basins are vulnerable to water scarcity and/or a surplus of water as well in the future. Therefore, the findings of this research are very important to plan proactive solutions in advance to manage the basin water resources efficiently.
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
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
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.
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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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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
Service life prediction under chloride-induced corrosion based on rapid chloride penetration test
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Karunaratne, PT; Weerasinghe, TGPL; Nanayakkara, SMA; Mallikarachchi, C
Concrete is a highly heterogeneous composite material that is widely used in the construction industry. At present with the development of new constituent materials, the durability of concrete is the key factor in the service life predictions of structures. The durability of concrete can be defined as its ability to resist against any sort of deterioration which depends on the interaction with the service environment. This project mainly focuses on chloride-induced corrosion and its effects on durability. Rapid Chloride Penetration Test (RCPT) is a rapid indication of resistance for the penetration of chloride ions which depends on the pore structure and pore solution characteristics. This project examines the effect of fly ash content and curing period on RCPT. Results have shown that there is a significant effect of those two factors on RCPT. In addition, relevant compressive strength gain over a period of 28 days is also discussed. Once the RCPT was completed, the chloride profile was obtained by collecting concrete powder samples at different depths. Obtained chloride profiles were fitted into a nonlinear regression analysis, and chloride penetration depths were calculated. Thereafter, the chloride diffusion coefficient was determined from Fick’s second law using chloride profile and chloride penetration depth. It was observed that the RCPT results can be directly used to determine the chloride diffusion coefficient based on the expected chloride concentration as those two parameters show a linear relationship. Finally, a performance-based design approach was proposed to correlate RCPT values with Fib Model code 2010, in order to predict the service life of corrosion affected - uncracked concrete.
item: Conference-Abstract
Numerical investigation of wind effects on roof-mounted objects with various shapes
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Kudagama, BJ; Weerasuriya, AU; Lewangamage, CS; Mallikarachchi, C
Wind flow over low-rise buildings is quite complicated because of the flow separation over the roof. Accordingly, wind flow over roof-mounted objects such as water tanks, solar panel arrays, solar water heaters, and chimneys mounted on a low-rise building can drastically influence the flow patterns and pressure distribution on roofs and the object. A series of Computational Fluid Dynamics (CFD) simulations were conducted to estimate the drag forces on objects and lift forces on the roof. Different shapes of objects were modelled on the leeward and windward slopes of a gable roof to estimate their susceptibility to wind damage. Wind-induced pressure on roofs was estimated to investigate how these objects affect the wind flow over the gable roof. This study gives suggestions for the selection of the best aerodynamic shape, orientation, or installation location for a certain roof-mounted object to avoid wind damage. The lift coefficients showed a variable change with different shapes of objects mounted on the windward and leeward slopes of the roof. The results showed that the objects mounted on the windward slope are more prone to wind damage as they experienced the largest wind loads, and objects with sharp edges experience the highest drag forces. The solar panel array mounted on the leeward slope closer to the ridge showed a 51% reduction in lift coefficients and the solar panel array mounted in the middle of the windward slope showed a 42% increase in lift coefficients compared to the bare roof case. Finally, this study recommends that it is safer to mount objects on the leeward slope and mounting a solar panel array on the leeward slope closer to the ridge can reduce the overall lift force acting on the roof of a low-rise gable roof building. Also, this study recommends avoiding solar panel arrays installed at the middle of the windward slope as it can compromise the safety of both the object and the roof.
item: Conference-Abstract
Study on methods and applications for assessing climate change vulnerability in Kalu and Kirindi oya river basins and consequences on surface water-groundwater interaction
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Mudalige, RN; Rajapakse, RLHL; Mallikarachchi, C
Climate change has influenced long-term rainfall patterns, with wet zones getting wetter and the inverse occurring in the dry zone, posing severe implications in water resource analyses and management. This has become a major issue in dry zone watersheds since baseflow is crucial in maintaining dry period streamflow. The main objective of this research is to identify tools and applications for assessing climate change vulnerability in the Kalu river basin at Ellagawa from the wet zone and the Kirindi Oya river basin at Thanamalwila from the dry zone, as well as to assess the climate change impacts on surface water-groundwater interaction in these zones. Before selecting any modelling tool, a comprehensive study on tools and indicators that are used for climate change vulnerability assessment was carried out. The accessibility, validity, and adaptability of multiple hydrological models were identified, and considering them, HEC-HMS was selected as the runoff modelling tool. After considering the benefits and drawbacks of several objective functions in runoff modelling, the mean ratio of absolute error (MRAE), R-squared correlation (R2), and Nash Sutcliff objective function (NASH) were chosen as objective functions. For the Ellagawa subbasin, the NASH value, R2 and MRAE were 0.63, 0.85, and 0.18, respectively while for the Thanamalwila sub-basin, the goodness of fit were 0.77, 0.87, and 0.45, respectively in calibration period. In the validation period, for the Ellagawa sub-basin, the NASH value, R2 and MRAE were 0.67, 0.83, and 0.49, respectively and for the Thanamalwila sub-basin, the values were 0.60, 0.69, and 4.47, respectively. Therefore, objective function values demonstrate that the models perform well in both watersheds. According to the sensitivity analysis of model parameters, impervious percentage, recession constant and ratio to the peak can be considered the most sensitive parameters. When impervious percentage, recession constant and ratio to peak change from -50% to 50%, the MRAE value shows the highest percentages changes as 119%, 131%, and 160%, respectively and the NASH value shows the highest percentages changes as 24%, 21%, and 69%, respectively. Time of concentration and soil percolation can be considered the least sensitive parameters. To assess the climate change vulnerability of the basins, synthetic climatic change scenarios were considered. Considering all the climate change combinations, change in mean annual streamflow will vary between -42% to 30% and -36% to 32% for the Ellagawa watershed and Thanamalwila watershed, respectively, and mean annual groundwater flow will vary between -56% to 27% and -32% to 62% for Ellagawa watershed and Thanamalwila watershed, respectively for the two selected scenarios. From the results obtained, it can be identified that the wet zone basin is more vulnerable in terms of streamflow changes and less vulnerable in terms of groundwater flow changes than the dry zone basin. For future studies, HEC-HMS can be recommended as a feasible and less complicated modelling tool for runoff simulation.
item: Conference-Abstract
Parametric modelling and analysis of tensegrity structures
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Samarawickrama, SKSR; Herath, HMST; Mallikarachchi, C
Tensegrity structures are based on a set of discontinuous compressible elements within a network of continuous tension elements, with isolated compressed elements (struts or bars) and prestressed tension elements (tendons or cables) that form a stable network. They are dominated by tensile elements, while more material-intensive compression elements are minimised. Tensegrity structures fail mainly due to low material efficiency, member instability, and excessive deflections when compared to rigid structures made with slender elements. The spatial geometry, axial stiffness, member layout, and connectivity of tensegrity structures directly affect the type of structural failure, including strength, instability, and stiffness. This study presents a systematic parametric study on overall axial stiffness variation of the 3-bar tensegrity prism to check the effect of the level of prestressing and other geometric parameters such as the height of the tensegrity cell, type of the tensegrity cell (number of compression members), radius of the tensegrity cell, area of the cables & struts, twisted angle of the top and bottom cable tringles, and the point load acting on nodes. The tensegrity unit studied here is the T3- prism. It is also termed 3-bar tensegrity. The 3-bar tensegrity has nine cables and three struts in which struts are isolated from each other. The cables are assumed to have solid circular cross-sections whereas struts are assumed to be circular hollow to achieve an optimum structure. All members of tensegrity structures are either loaded in axial compression or tension. This means the structure will only fail due to cable yield or buckling of struts. Since the compression members are not transmitting loads over a longer distance, they are not subject to higher buckling loads. The prestressed cables are mostly used for these structures to have better stability to resist higher deflections. In this study, a 3- bar tensegrity cell was analysed using parametric modelling by applying three-point loads in the z-direction to the cell's top nodes. In order to determine the minimum mass necessary under yielding constraints, the static analysis optimises the tensile forces in the cables and the compressive forces in the struts in the presence of certain external forces. In order to acquire the parametric results of the 3-bar tensegrity cell, the Karamba3D structural analysis tool was utilised. It is fully embedded within the Grasshopper parametric design environment, a plug-in for the Rhinoceros3D computer-aided design program. The tensegrity cell's stability improves with height, which also causes an increase in mass and displacements. When the radius, type, and point loads acting on the tensegrity cell increase, the tensegrity cell tends to become more unstable, leading to cell instability because of poor stress distribution among the members. The tensegrity cell becomes more stable while simultaneously increasing its mass by increasing its compression area, tension area, and twisted angle. As a result, while designing the optimised design, mass and stability should both be taken into consideration. Most of the tensegrity structures are constructed by combining diverse types of general tensegrity configurations. After modelling and finalising the solutions for tensegrity configurations, an optimum tensegrity geometry for any application can be defined by combining and scaling these basic tensegrity configurations.
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
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.

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