Browsing by Author "Weerasinghe, TGPL"

Now showing 1 - 13 of 13

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-Full-text
Determination of tensile strain capacity of fresh concrete
(Department of Civil Engineering, University of Moratuwa, 2015-10) Weerasinghe, TGPL; Nanayakkara, SMA; Hettiarachchi, MTP
Measuring physical properties of fresh concrete is important to understand the behavior of the early phase of concrete. The measurement of tensile strain capacity of fresh concrete predicts the risk of cracking due to restrained shrinkage. Fresh concrete means the concrete before the hardening phase which is still in a semi liquid state. i.e. from right after mixing of concrete to 3 – 4 hours. Several research studies have been conducted but complex test methods have been developed to measure both stress and strain and the average strain was measured. The paper contains the procedure adopted to develop a simple test method to measure the local strain along a sample. After verifying the test method, influence of cement type for early age tensile strain capacity was studied. Ordinary Portland Cement, Fly ash blended and Portland Limestone Cement were used. Concrete was mixed as a large quantity and kept inside the mixer and agitated every 10 minutes before being taken out for testing. The method simulates the conditions where concrete is produced and kept inside a truck mixer for a while before placing. Results indicate that fly ash blended concrete has a higher tensile strain capacity than other cement types thus the mix is less vulnerable for early age cracking. Further tests should be done to determine the influence of cement type for tensile strain capacity of undisturbed concrete.
item: Conference-Full-text
Determination of Tensile Strain Capacity of Fresh Concrete: A new test method
(2016-01-06) Weerasinghe, TGPL; Nanayakkara, SMA
Measuring physical properties of fresh concrete is important to understand the behaviour of the early state of concrete. Plastic shrinkage occurs at the very early stage due to evaporation of water from the concrete surface. When concrete is restrained against plastic shrinkage, tensile strain is developed and when it exceeds the tensile strain capacity, cracks occur. This phenomenon is called as plastic shrinkage cracking. In order to assess the risk of plastic shrinkage cracking tensile strain capacity of fresh concrete should be measured. Fresh concrete means the concrete before the initial setting time which is still in a semi liquid state. The paper presents a test method developed to measure the strain distribution along a fresh concrete sample. Based on this test method tensile strain capacity of a selected mix proportion with three different types of cements, i.e., Ordinary Portland Cement, Fly ash blended and Portland Limestone Cement were determined. Results indicate that concrete with fly ash blended cement has a higher tensile strain capacity than other two cement types.
item: Thesis-Full-text
Evaluation of risk of plastic shrinkage cracking in concrete
Weerasinghe, TGPL; Nanayakkara, SMA
Plastic shrinkage cracking is a common phenomenon associated with concreting in hot and windy weather. Excess evaporation of bleed water causes loss of water from the concrete surface and plastic shrinkage occurs due to that at very early age i.e. within first 4-6 hours. Tensile strain will be developed as a result of this shrinkage and cracking will occur when it exceeds the tensile strain capacity of concrete The measurement of tensile strain capacity of fresh concrete is important to predict the risk of plastic shrinkage cracking. Data on strain capacities at the very early age i.e during first few hours is hard to determine as concrete is still in fresh state. The report contains the procedure adopted to develop a simple test method to measure the local strain along a sample of fresh concrete. The influence of cement type, fine aggregate type and mortar phase for the strain capacity was studied. Results indicate that the addition of fly ash and manufactured sand has increased the tensile strain capacities. In order to evaluate the risk of plastic shrinkage cracking it is necessary to develop a model to simulate strain development in fresh concrete due to plastic shrinkage. First, key factors affecting shrinkage, bleeding and evaporation, were modeled and the starting time of drying was identified. Subsequent loss of water was calculated and incorporated in a finite element model to simulate the tensile strain development. Calculated strains were very similar to the measured strains and therefore the model can be used to predict the development of early age tensile strain due to plastic shrinkage. Tensile strain capacities determined from the test and the modeled strain development were compared to evaluate the risk of plastic shrinkage cracking in concrete with OPC and fly ash. Although there was an increase in strain capacity of concrete with fly ash blended cement, model predicted that the risk of cracking was higher in concrete with fly ash blended cement as there was a significant increase in strain developed as a result of drying. Further experimental studies are needed to prove the prediction and also to find the influence of other factors (PLC and admixtures) to plastic shrinkage cracking in concrete.
item: Conference-Abstract
Investigation of the feasibility of electrochemical extraction of chloride (Cl) in retrofitting reinforced concrete structures in the coastal areas
(Department of Civil Engineering, University of Moratuwa, 2024) Lokuge, US; Nanayakkara, SMA; Weerasinghe, TGPL; Pasindu, HR; Damruwan, H; Weerasinghe, P; Fernando, L; Rajapakse, C
Corrosion of steel reinforcement is one of the primary modes of deterioration in reinforced concrete structures worldwide, largely driven by chloride attacks from marine environments, de-icing salts, and other sources of chloride ingress. This type of deterioration significantly compromises the structural integrity of concrete, leading to costly repairs and frequent maintenance. Every year, a staggering amount of money is spent on retrofitting and reconstructing these damaged structures, which has prompted extensive research into effective repair and rehabilitation methods. Among the various techniques studied, Electrochemical Chloride Extraction (ECE) has emerged as a promising method for retrofitting deteriorating reinforced concrete structures subjected to chloride attacks. ECE works by applying an electrical current to the concrete, which drives chloride ions away from the embedded steel reinforcement, thereby reducing the risk of corrosion. However, due to the lack of proper standards and guidelines on this method, it has not been widely adopted in the industry. This study aims to quantify the efficiency of chloride extraction and to determine the positive and negative side effects of using ECE as a treatment method for chloride-contaminated reinforced concrete structures through comprehensive laboratory tests. A major challenge in applying ECE in real-world scenarios is the difficulty of immersing large-scale structures in an electrolyte solution. To overcome this, a novel test setup was designed that simulates in-situ conditions and can be scaled up for industry applications. The research focused on monitoring the variation of chloride concentration in both the concrete and the electrolyte solution, assessing these variations over time, depth, and chloride-to-cement ratios of the test specimens. The study also explored the effects of ECE on the physical, mechanical, and chemical properties of the concrete to provide a holistic evaluation of its impact on structural performance. The results of this investigation indicate that ECE can effectively extract chloride ions from concrete, highlighting its potential as a viable corrosion mitigation technique. The study emphasizes the importance of optimizing experimental parameters, including the current density, duration of treatment, and composition of the electrolyte, to enhance the efficiency of chloride removal. Additionally, the development of practical testing methodologies bridges the gap between laboratory research and real-world applications, offering engineers and practitioners valuable guidance for implementing ECE in the field. This research underscores the need for standardized procedures and guidelines to facilitate broader industry adoption of ECE, ultimately enhancing the preservation of aging concrete structures. The findings contribute significantly to improving corrosion mitigation techniques and provide crucial insights for professionals involved in infrastructure maintenance and rehabilitation, paving the way for future advancements in the field.
item: Conference-Full-text
Modelling of early age tensile strain development of fresh concrete
(IEEE, 2016-05) Weerasinghe, TGPL; Nanayakkara, SMA; Jayasekara, AGBP; Bandara, HMND; Amarasinghe, YWR
Plastic shrinkage cracking is a common phenomenon associated with concreting in hot and windy weather. Excess evaporation of bleed water causes loss of water from the concrete surface and plastic shrinkage occurs due to that at very early stage i.e. within the first 4-6 hours. Tensile strain will be developed as a result of this shrinkage and cracking will occur when it exceeds the tensile strain capacity of concrete. This paper is aimed at developing a model to simulate such behavior and determine the tensile strain development with time. First, key factors affecting shrinkage, bleeding and evaporation, were modelled and the starting time of drying was identified. Subsequent loss of water was calculated and incorporated in a finite element model to simulate the tensile strain development. Calculated strains were very similar to the measured strains and therefore the model can be used to accurately predict the development of early age tensile strain due to plastic shrinkage.
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.
item: Conference-Full-text
Numerical modeling of char layer falling off in cross-laminated timber (CLT)
(IEEE, 2023-12-09) Naveen, GWK; Weerasinghe, TGPL; Karannagodage, C; Kleinhenz, M; Abeysooriya, R; Adikariwattage, V; Hemachandra, K
This paper focuses on investigating the thermal behavior of Cross-Laminated Timber (CLT) panels under hightemperature conditions, with a particular emphasis on the delamination of CLTs and their impact on their thermal properties. The study utilizes a finite element method (FEM) model developed using SAFIR software to simulate the behavior of CLT panels exposed to various high-temperature scenarios. The thermal properties derived from the Eurocode 5 and newly obtained properties are compared to assess their accuracy in capturing the post-fall-off behavior of CLT. It is found that the Eurocode data lacks calibration to accurately represent the behavior of CLT after the first fall-off of the fire protection system or when a charred CLT layer is present. A new set of thermal properties specifically tailored for CLT subjected to standard fire conditions is proposed to address this limitation. The simulation results indicate that the newly obtained thermal properties align well with the experimental data, demonstrating their improved reliability in capturing the thermal behavior of CLT. These findings contribute to the development of more accurate fire-resistant design strategies for CLT structures, enhancing their safety and performance in high-temperature environments.
item: Conference-Abstract
Numerical modeling of char layer falling off in crosslaminated timber (clt)
(Department of Civil Engineering, 2023-09-27) Naveen, GWK; Weerasinghe, TGPL; Karannagodage, C; Kleinhenz, M; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
Cross-laminated timber (CLT) is widely acclaimed in modern construction for its structural prowess, aesthetics, and sustainability. Architects, engineers, and designers increasingly favour this versatile material. Nonetheless, an in-depth exploration of CLT's thermal properties is essential. These properties, including heat transfer, charring, and insulation, significantly impact CLT structures' fire resistance and thermal efficiency. The thermal characteristics of timber, which encompass properties like density, thermal conductivity, and heat capacity, significantly influence its response to fire. As timber undergoes heating, it undergoes pyrolysis, leading to chemical and physical transformations that impact its ignition, combustion, and extinguishing behaviour. Therefore, understanding how thermal properties like thermal conductivity, specific heat, and thermal diffusivity evolve as timber is exposed to elevated temperatures is of utmost importance. While prior research has addressed these thermal properties and integrated them into Eurocode 5, their applicability to CLT is not straightforward. CLT exhibits distinctive behaviour at high temperatures, deviating from traditional timber types. In CLTs, a unique phenomenon arises under elevated temperatures, characterised by the delamination of CLT panels. Delamination occurs when the temperature within the panel exceeds the glass transition temperature of the adhesive, resulting in adhesive softening and a loss of strength. Consequently, the internal layers of CLT become exposed to the fire, lacking the protective char layer characteristic of other timber types. This intricacy necessitates dedicated research on CLTs' thermal properties and behaviour under extreme heat conditions. This study is dedicated to unravelling the intricacies of CLT panels' thermal behaviour when subjected to high temperatures, explicitly focusing on delamination and its repercussions on thermal properties. Leveraging advanced finite element method (FEM) modelling, developed using SAFIR 2016 software, the study orchestrates simulations replicating CLT panels' response to various high-temperature scenarios. To benchmark these simulations and derive meaningful insights, the study juxtaposes the thermal properties stipulated in Eurocode 5-1-2 (2004) with newly derived properties. This rigorous analysis reveals a misalignment between Eurocode data and the real-world behaviour of CLT, especially in the post-fall-off phase of the fire. Consequently, the study introduces a novel thermal property tailored explicitly for CLT under standard fire conditions (ISO-834). Crucially, the simulations validate the fidelity of the newly derived thermal properties in replicating the actual thermal behaviour of CLT, as substantiated by experimental data. These findings rectify prior inaccuracies and lay the foundation for developing more precise fireresistant design strategies for CLT structures. Ultimately, this research significantly enhances the safety and performance of contemporary timber buildings operating within hightemperature environments.
item: Conference-Abstract
Predicting fire-induced spalling in concrete tunnel linings using machine learning techniques
(Department of Civil Engineering, 2023-09-27) Sembanayake, SMDT; Weerasinghe, TGPL; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
Fire-induced spalling is the phenomenon where the outer cracked or delaminated layer of a concrete element detaches due to the exposure to high temperatures during a fire. Spalling is a phenomenon that has raised concerns in the research community since the 19th century. Since then, many experimental, analytical, numerical, and other studies have been conducted around the world to explain this phenomenon. However, an accurate model to predict the occurrence of spalling remains elusive, particularly for tunnel linings. Tunnel fires have drawn increasing attention and raised more concerns in recent decades. The rapid growth of freight transportation, particularly flammable ones such as fuel, increases the potential to cause a rapid-fire spread. When compared to building fires, tunnel fires can be more destructive due to their high temperatures, quick heating rates, prolonged duration, and uneven temperature distribution inside the tunnel. Spalling is a complex phenomenon with a high degree of randomness that interdepends on too many factors. The occurrence of spalling phenomena is significantly influenced by various microstructural properties of concrete. Internal factors such as concrete permeability, moisture content, water-cement ratio, and aggregate type have a significant impact on spalling. Furthermore, temperature, heating rate, humidity, and loading conditions are some of the external factors that affect spalling. To gain a comprehensive understanding of this phenomenon, it is crucial to consider the interdependencies among these various factors and their combined effects. The current method used in industry to evaluate the performance of a concrete tunnel lining is to test the specimen in large-scale furnaces. However, this method has several limitations. It requires the use of large-scale furnaces, which is time-consuming, expensive, and difficult to replicate due to their dependence on specific concrete mixtures and test setups. Alternative approaches, such as Machine Learning (ML), can be considered to overcome these challenges. Recent advancements in data analytics & ML have demonstrated their capability to solve such complex problems. This study aims to create a framework for predicting fireinduced spalling in tunnel linings using several ML techniques. Python programming language was utilised to develop this framework and Jupyter Notebook was used as the web based interactive platform. Using the previously published fire test data, a new dataset was created, and after performing the appropriate preprocessing, it was fed into 10 distinct ML techniques. These includes 7 ensemble techniques and 3 traditional ML techniques. Then the developed model was further refined using hyperparameter tuning & kfold cross-validation techniques. The results of this model revealed that it is possible to forecast the occurrence of spalling with an accuracy of more than 90% using ensemble ML techniques.
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
Use of industrial waste sludge in concrete paving blocks
(Department of Civil Engineering, 2023-09-27) Basnayaka, BMI; Weerasinghe, TGPL; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
The interdependence of a nation's economic momentum with the dynamism of its manufacturing sector is evident. The era of rapid industrialisation brings with it an escalated output of waste. Addressing this surge, particularly regarding the proper management, disposal, or recycling, is paramount, especially when we contemplate the long-term repercussions on both environmental sanctity and public health. While suppressing industrial expansion or sanctioning unchecked waste release might seem like solutions, they are not in the best interests of sustainable economic and environmental goals. Given these challenges, there's a pressing international drive toward converting waste into purposeful, usable products. In the vast spectrum of industrial waste, sludge emerges as a significant player. This semi-fluid substance, replete with solids and liquids, is a by-product of various water treatment processes. Its nature, whether organic or inorganic, hinges on the kind and extent of contaminants it contains. Through dehydration, one can transform sludge into a more manageable powdered form. This research casts its lens on the potential of this powdered sludge, a derivative of industrial waste, in concrete paving block construction. The vision here is twofold: advancing towards a greener paving methodology and finding a viable solution to the ever-present sludge disposal issue. The initial stages of the study focused on meticulous chemical scrutiny of the sludge, followed by a sieve assessment to understand its granular composition. Notably, while the granular profile resonated with that of typical fine aggregate, the chemical analysis underscored the dominance of organic particles. Acting on this knowledge, experimental blocks were crafted, with the sludge powder replacing traditional materials like cement and sand. However, these modified blocks manifested a noticeable reduction in compressive strength when juxtaposed against standard concrete blocks. For a deeper dive into the composition, tools like Scanning Electron Microscopy (SEM) were employed to decipher micro-level structures, and Energy-Dispersive X-ray Analysis (EDAX) was used to identify elemental makeup. These sophisticated analyses pinpointed weaker components that did not bolster the material's inherent strength. In a promising turn of events, refining the sludge to purge these weaker elements led to a notable enhancement in block strength, aligning it with industry benchmarks. With these findings at hand, the recommendation is to broaden the scope of research, perhaps by exploring diverse mix ratios, to further optimise the efficiency and application of this innovative approach.
item: Conference-Abstract
Use of waste rubber granules for the production of concrete paving blocks
Gamalath, HGP; Weerasinghe, TGPL; Nanayakkara, SMA
Worldwide uses of rubber products are increasing every year. A significant proportion of waste rubber is generated during the manufacturing process of rubber products, and the disposal of such waste has been a problem due to the non-degradable complex structure of rubber and categorized as hazardous waste. Therefore, disposal of waste rubber as landfill is considered as environmentally unfriendly. However, waste rubber can be used as a replacement of coarse and fine aggregates in concrete for paving blocks for use roadways and walkways. Previous studies have shown that adding waste rubber increases the skid resistance and decreases abrasion resistance while making it more flexible. However, compressive strength get reduced with the addition of rubber waste. Therefore, further studies are necessary to find a balance between the desired properties and come up with an optimum mix design for rubberized concrete. Most of previous studies are related to use of crumb rubber (waste from rubber tires). Therefore, an attempt has been taken by carrying out an experimental study to develop a mix which gives the required compressive strength with the highest proportion of waste rubber content in the mix to give a value addition to this waste product.