Browsing by Author "Dias, WPS"

Now showing 1 - 20 of 96

item: Thesis-Abstract
A Systems approach to assess the vulnerability of buildings to bomb blast
Chandratilake, SRMSR; Dias, WPS
A blast event lies within the social system and involves people. Hence vulnerability to blast loading can be considered a socio-technical or "soft" system, where our ability to model and hence predict bounds on behaviour is poor. Even where the "hard" part of the system is concerned (i.e. structural response), blast loading is difficult to idealize and its effects cannot be fully predicted. For all the above reasons, the analysis of vulnerability to blast loading must be grounded in past experience. Grounded Theory is a way in which theory is built from phenomena. Theory is considered as being grounded in phenomena; the reliability of data forms the basis for claiming the phenomena exist. Once the specific phenomena in the different case studies have been identified, they can be generalized into concepts. Coherence among concepts is the appropriate grounds for theory formation and acceptance. Grounded Theory is "explicity emergent" and does not test a hypothesis. For the above reasons, Grounded Theory was used to structure this ill-structured research problem that also required a reliance on experience. The main objective of the study was to construct a hierarchy of concepts, which would constitute aspects that contribute to building vulnerability, using case histories. "Vulnerability" is treated as the top level concept, itself consisting of other concepts. Ten case studies of blast loading .were chosen. These represented a variety of building uses, structural form and construction material, and also reflected a variety of explosive types and different locations worldwide. Data (e.g. statements) from case histories were used to identify phenomena. It was possible to extract 63 phenomena relating to building vulnerability from these case studies; some concepts were repeated in the case study phenomena. It was observed that the concepts lent themselves to hierarchical structuring. Some of the concepts could be grouped into a single concept that "emerged" from the former. The 63 original phenomena were used to generate 52 concepts, at various levels in the hierarchy. The hierarchy that was constructed consisted of seven levels. Each emergent concept can be called a "holon" - i.e. it is a whole when considering its constituent lower level concepts, and a part when considering an emergent higher level concept it contributes towards. The top levels of the hierarchy obtained differed somewhat from those that were previously constructed using "top down" approaches based largely on literature surveys; this demonstrates the value of a "bottom up" approach that seeks to "listen to the data" from case studies. Level 2 of the hierarchy shows that the vulnerability due to blast effects is a social process where context too plays a key role; hence due consideration must be given to context when seeking to assess or reduce vulnerability. Some of the concepts that were frequently repeated in the case study phenomena are "advance warning", "standoff distance", "nature of terrorism", "confinement", "building layout", "structural redundancy", "security" and "glass"; a method of weighting is required to account for the importance of such concepts (reflected in their repetition) within the hierarchy. The assessment procedure combines existing numerical models as well as ways of processing vague information and expert judgments. It is also a very flexible tool which allows the handling of various types of artifacts which are significantly different from past experience. Experts will use linguistic assessments to measure the evidence about the dependability of holons to sustain their function in a particular blast incident. Linguistic assessments are matched to interval probability numbers. An interval number is used to capture, in practical manner, features of fuzziness and incompleteness. Interval Probability Theory (IPT) is used to combine evidential support values throughout the hierarchy. A computer implementation of the model was developed to show its potential for practical use. The software developed was used to apply the methodology to a building located in the heart of Colombo. The interpretation of results shows the potential of the model to be used as a management tool for practical decision making.
item: Conference-Abstract
Acheap and environmentally friendly process to manufacture caustic soda
(Engineering Research Unit, Faculty of Engiennring, University of Moratuwa, 1995-03) Perera, SAS; Dias, WPS
item: Article-Full-text
Are environmental sustainability and happiness the keys to prosperity in Asian nations?
(Elsevier, 2020) Kaklauskas, A; Dias, WPS; Binkyte-Veliene, A; Abraham, A; Ubarte, I; Randi, OPC; Siriwardana, CSA; Lil, I; Milevicius, I; Podviezko, A; Puust, R
Various research prove that happy nations are prosperous in numerous areas containing GDP, productivity, social support and inclusion, health, lower corruption and environmental sustainability. The analysis in this multicriteria study covers the environmental sustainability, success and happiness trends in Asian nations during a 25-year time span. Strong and average correlations amongst the success, happiness and environmental sustainability, of Asian nations, in one regard, and, in another regard, the macroeconomics, well-being and human development, values-based, quality of life and environmental indicators were established across numerous statistical databases. Six multiple regression models of success and happiness in Asian nations were compiled with the assistance of IBM SPSS Statistics. The linear regression model of success in 40 Asian nations illustrates how nine independent variables explain 90.7 percent of the significances of results. The 19-Asian nation, multiple regression happiness model show how 16 independent variables account for 99.5% of the Happiness index weight dispersion.
item: Conference-Full-text
Artificial neural networks for construction bid decisions
(Engineering Research Unit, Faculty of Engiennring, University of Moratuwa, 1995-03) Dias, WPS; Weerasinghe, RLD; Dias, WPS
An Artificial Neural Network (ANN) approach was explored for supporting construction bid decisions, since such decisions are heavily dependent on practitioner expertise, which in turn is generally encapsulated in case histories. One of the ANNs described here was trained on knowledge from a sample of the entire Sri Lankan construction industry, and was used to predict the preferred job sizes for firms of differing characteristics; such information could help firms in their bid/no-bid decisions. The other ANN was trained on case histories elicited from a single contractor, and was used to predict the percentage mark-up. The network outputs were obtained in both binary output and continuous valued output formats. The former format had some distinct advantages over the latter, as it provided greater information for decision making instead of being a "black box" output. The influences of the middle layer size, output format and allowable error during training, on the training duration and accuracy of prediction were studied.
item: Article-Full-text
Basic creep of unsealed hardened cement paste at temperatures between 20°C and 725°C
(Institution of Civil Engineers, 1987) Dias, WPS; Khoury, GA; Sullivan, PJE
A definition for basic creep at elevated temperatures is arrived at, based on the time at which load is applied. Experimental results are presented for the basic creep of hardened cement paste and comparisons are made with the behavior of various concretes. The time function of basic creep is shown to follow a power law relationship, whereas the temperature function indicates that a rheological property, seated in the cement paste itself, would limit the structural usefulness of Portland cement-based concretes to below 600°C. Preheating to temperatures higher than the creep test temperature reduces the creep potential in general.
item: Conference-Full-text
Biomethanation studies at university of moratuwa
(Engineering Research Unit, Faculty of Engiennring, University of Moratuwa, 1995-03) sivapathasundaram, R; Wanigasekara, N; De Alwis, AAP; Dias, WPS
Biogas generation or Biomethanation offers a viable option in simultaneous solid waste management and energy generation. The technology is quite well developed and is not only confined to developing countries as commonly perceived by many. However, the scale of practice and the objectives in developing and developed countries vary. A biogas program has been active in Sri Lanka as well, though this has not achieved the popularity or acceptance as in countries like China, India and Nepal. The Sri Lankan program however, has been successful in giving rise to a new design which is termed the Dry Batch digester. The work has been mainly done by the National Engineering Research and Design Centre (NERD). The concept is different to the two main types due to the use of an essentially ‘dry* mixture of organic waste, and the batch type operation. In urban areas biomass such as straw or animal wastes such as cowdung cannot be found in such quantities to have biogas systems of continuous nature. The NERD version of batch type could be effectively employed in institutions where organic wastes are generated, or to employ solid wastes such as market garbage. Their biomethanation kinetics favour the batch approach. The objective of the research program undertaken by the Department of Chemical Engineering was to do detailed evaluation of scientific, technological and social aspects of biogas systems as a means of pollution prevention with simultaneous energy generation. Laboratory studies have been done on various industrial waste streams ranging from food processing wastes to textile industry effluents which arc quite toxic to micro-organisms in general. This paper introduces the basic concepts and some of the methodologies followed by the research team. To support dissemination of biogas technology, a pictorial step-bystep guide detailing out all stages involved in the building and operation of a digester and a gas holder system has been prepared as part of this work.
item: Article-Full-text
Characterizing fracture stress of defective graphene samples using shallow and deep artificial neural networks
(Elsevier, 2020) Dewapriya, MAN; Rajapakse, RKND; Dias, WPS
Advanced machine learning methods could be useful to obtain novel insights into some challenging nanomechanical problems. In this work, we employed artificial neural networks to predict the fracture stress of defective graphene samples. First, shallow neural networks were used to predict the fracture stress, which depends on the temperature, vacancy concentration, strain rate, and loading direction. A part of the data required to model the shallow networks was obtained by developing an analytical solution based on the Bailey durability criterion and the Arrhenius equation. Molecular dynamics (MD) simulations were also used to obtain some data. Sensitivity analysis was performed to explore the features learnt by the neural network, and their behaviour under extrapolation was also investigated. Subsequently, deep convolutional neural networks (CNNs) were developed to predict the fracture stress of graphene samples containing random distributions of vacancy defects. Data required to model CNNs was obtained from MD simulations. Our results reveal that the neural networks have a strong ability to predict the fracture stress of defective graphene under various processing conditions. In addition, this work highlights some advantages as well as limitations and challenges in using neural networks to solve complex problems in the domain of computational materials design.
item: Article-Full-text
Circular organizational structure for project teams
(1990) Dias, WPS
A project team, working on a short contract research assignment and with a large number of professionals, is led by a project manager, who is on a peer level with many coworkers but hierarchically below others. This combination of conditions results in the evolution of a circular organizational structure, which reflects a high degree of informal interaction and gives a central role to the project manager, as opposed to an apical position to the project director. This structure can be considered to be a hybrid of two small‐group organizational structures, incorporating both the ideas of leadership and interaction. The project manager's key managerial role is that of facilitator, especially regarding the flow of information and the optimization of team members' time inputs. In addition, since he is responsible for two of the final tasks in the project, he occupies a natural position of coordination and control.
item: Article-Full-text
Comparing the systems approaches of Checkland and Blockley
(2014-06-26) Dias, WPS
It is argued that systems approaches from even different backgrounds can nevertheless end up with similar features, promoting the idea that such approaches are grounded in reality, as science is taken to be. The systems approaches of Peter Checkland and David Blockley, from management and engineering backgrounds, respectively, are explored with a view to highlighting similarities and differences. This is done by looking at summaries of their approaches and examples of their use. Both Checkland's and Blockley's approaches have a set of common features such as layers; purpose; top-level outcome; attributes such as what, how and why; measures; uncertainty and conversation. Such similarities prompt us to see systems approaches as being objective rather than relativistic. The differences in their overall approaches reflect the hierarchically structured nature of reality that requires hierarchically ordered approaches to deal with it. Â© 2013 Â© 2013 Taylor & Francis.
item: Article-Abstract
Comparing the systems approaches of checkland and blockley
(2015-08-20) Dias, WPS
It is argued that systems approaches from even different backgrounds can nevertheless end up with similar features, promoting the idea that such approaches are grounded in reality, as science is taken to be. The systems approaches of Peter Checkland and David Blockley, from management and engineering backgrounds, respectively, are explored with a view to highlighting similarities and differences. This is done by looking at summaries of their approaches and examples of their use. Both Checkland's and Blockley's approaches have a set of common features such as layers; purpose; top-level outcome; attributes such as what, how and why; measures; uncertainty and conversation. Such similarities prompt us to see systems approaches as being objective rather than relativistic. The differences in their overall approaches reflect the hierarchically structured nature of reality that requires hierarchically ordered approaches to deal with it.
item:
Comparing the systems approaches of Checkland and Blockley
Dias, WPS
It is argued that systems approaches from even different backgrounds can nevertheless end up with similar features, promoting the idea that such approaches are grounded in reality, as science is taken to be. The systems approaches of Peter Checkland and David Blockley, from management and engineering backgrounds, respectively, are explored with a view to highlighting similarities and differences. This is done by looking at summaries of their approaches and examples of their use. Both Checkland’s and Blockley’s approaches have a set of common features such as layers; purpose; top-level outcome; attributes such as what, how and why; measures; uncertainty and conversation. Such similarities prompt us to see systems approaches as being objective rather than relativistic. The differences in their overall approaches reflect the hierarchically structured nature of reality that requires hierarchically ordered approaches to deal with it.
item: Conference-Full-text
Computer integration for sri lankan industries - a review
(Engineering Research Unit, Faculty of Engiennring, University of Moratuwa, 1995-03) De Silva, S; Wijesoma, WS; De Alwis, AAP; Dias, WPS
production and manufacturing industries employ obsolete methodologies. However with the advent of personal computers in the early 1980's the user community enlarged very rapidly. The telecommunication infrastructure has been enhanced in the last five years allowing private networks such as cellular methodology for computer interconnectivity. A good example of optimum use of these facilities is that of local private banks that open many branches on the Uni Bank principle using centralized host computer directly connected to the branches as well as ATMs at strategic locations in the city. Moreover the printing and publishing industry seems to have absorbed new computer based technology successfully where operations carried out are predominantly image acquisition, image setting and printing. This paper is an outcome of an ongoing survey carried out mainly to assess the areas of application and extent of computerization in the Industrial Sectors in Sri Lanka.
item: Article-Abstract
Concrete in the marine environment: a review with emphasis on tropical coastal applications
Dias, WPS
The effect of the marine environment on concrete depends on the climate and the zone of exposure. Degradation of concrete takes place due to a-self reinforcing permeation-chemical attack-cracking-permeation cycle.-Chemical attack can take place in the concrete or in the steel, if the concrete is reinforced. Cracking can occur due LO loading as well as physical and chemical phenomena, either internal or external. Permeation of both water and various harmful ions will depend on the quality of the concrete.
item: Article-Abstract
Condition assessment of a deteriorated cement works
Dias, WPS; Jayanandana, ADC
This paper describes the condition assessment of a 30 year old cement works, where some of the structures were clearly deteriorated. It was carried out for the purpose of obtaining material properties needed for evaluating strength and integrity, and for establishing durability. This was done by sampling the structures using the nondestructive techniques of visual inspection, perusal of drawings, ultrasonic pulse velocity measurements, covermeter surveys, and core testing. Core testing gave information not only about strength but also about sorptivity, carbonation, chlorides, and sulfates, and about the variation of some of these properties with depth from the concrete surface. Some new approaches were used to estimate the grade of concrete and the partial safety factor for reinforcement. The use of ‘‘twin cores’’ ~surface and internal! indicated that the surface quality of the concrete was actually better than the internal quality. Recommendations for repair and maintenance dealt with ~1! accumulated cement dust; ~2! concrete deterioration; ~3! areas experiencing elevated temperatures; and ~4! waterproofing of the concrete surface
item: Conference-Extended-Abstract
Cracks in masonry walls due to thermal movements of overlying slab
(2006) Dilrukshi, KGS; Dias, WPS
Concrete slabs exposed to direct sunlight experiences temperature related horizontal movements. In addition, temperatures on the top surface will be higher than those on the underside of the slab, causing an upward movement of the slab during heating. In a typical building, masonry and concrete structural elements restrain each other at their respective interfaces. Therefore, significant movements may be generated on the masonry walls, due to movement on roof slab. These movements can result in overstressing and cracking in masonry.
item: Article-Full-text
Dependencies among environmental performance indicators for buildings and their implications
(Elsevier, 2017) Dias, WPS; Chandratilake, SR; Ofori, G
Environmental performance rating schemes such as LEED allocate separate indicator scores for various criteria (or aspects). The overall environmental performance score is obtained by summing these separate scores. However, no mention is made regarding any dependencies among aspect indicators. In this study, possible influences, including their degree (‘strong’, ‘moderate’, and ‘none’) and direction (positive, negative) were identified among the seven aspects covering the sustainability of the building site (i.e. Site domain) in an environmental performance assessment scheme for buildings. These judgements were corroborated by the correlation coefficients corresponding to scores for those aspects achieved by 10 buildings. First and higher order influences were accounted for through a matrix-based scheme, which revealed aspects that were influencing others or being influenced by them. The degree of influencing other aspects was found to be inversely proportional to that of being influenced by them. The aspect weights, obtained by querying experts, appeared to be independent of their degree of influence. The negative dependencies in this Site domain gave rise to constraints on combinations of aspect scores and the maximum environmental performance score achievable. The score levels that would maximize this overall score were obtained through an optimization exercise; this generated some possible planning strategies.
item: Article-Full-text
Derivation of tsunami damage curves from fragility functions
(Springer Netherlands, 2019) Dias, WPS; Edirisooriya, U
Structural vulnerability due to tsunami loading can be characterized by a family of fragility curves, which are expressed as lognormal cumulative distributions of the conditional probabilities of reaching or exceeding various damage states for given values of the demand parameter, generally inundation depth. Such curves can easily be obtained from field surveys. However, what is required for risk analyses is total damage. This research presents a method of obtaining mean damage curves from fragility functions in the literature, using cost coefficients associated with each of four damage states. The curves are obtained for timber, masonry and reinforced concrete single-storey structures. They could also be fitted very well with negative power law expressions having two parameters, and quite well with negative exponential functions having just a single parameter (based on construction material) and the single independent variable of inundation depth. The damage curves can also be used to present the relative vulnerability of one construction material with respect to another; this could reduce the variability associated with different locations. The relative damage ratios for the different construction materials were found to be strongly dependent on inundation depth. Although there are large differences among construction materials at low depths, such differences disappear at depths of 6–10 m. Similarly, the effects of shielding and debris on damage were also found to be dependent on inundation depth. The results of this work can be used to introduce coupling effects into empirical relative vulnerability models that seek to incorporate many factors independently.
item: Article-Full-text
Design and development of alkali pozzolan cement (APC)
(Elsevier, 2014) Kulasuriya, C; Vimonsatit, V; Dias, WPS; De Silva, P
This paper describes the development of an environmentally friendly Alkali Pozzolan Cement (APC), a non-hazardous dry cement powder that incorporates a large percentage of fly ash but needs only ambient temperature curing in order to achieve strengths comparable to OPC controls. APC consists of fly ash, lime, an activator and OPC (a ‘scaffolding’ material). Scaffolding was the most statistically significant factor contributing to the compressive strength of APC paste specimens, compared to activation, age (3 days vs 28 days) and temperature (ambient vs 15 h at 60 C). SEM, EDS and XRD investigations were employed to explain variations in strength.
item: Article-Abstract
Developing an Approach to A ssess ‘Integral Sustainability’ of Alkali Pozzolan Cement
Kulasuriya, C; Vimonsatit, V; Dias, WPS
This paper presents the search of an approach to assess 'integral sustainability'of a new cement called 'Alkali Pozzolan Cement'(APC). It can also be considered as an investigation into the possibility of employing fundamental concepts of integral theory in civil engineering or in the building engineering industry. To employ integral theory in an engineering context, the authors first propose a modified AQAL tetraquadrant frame work.
item: Thesis-Abstract
Development and evaluation of the aesthetics of structural form
Kulasuriya, C; Dias, WPS; Hettiarachchi, MTP
This study demonstrates that the aesthetic concepts of engineering design do not just arise; but that they are derived from various models of aesthetics. It also presents various Proportioning Systems and their application in Structures, through case studies, notably the use of the Golden Proportion. The research includes two perceptual experiments. The first experiment was about the perception of rectangular shapes using one hundred respondents. The second experiment was about the perception of simple structures using fifty respondents. The results of these perceptual experiments confirm the fact that respondents' preferences are linked with the various philosophical models. The research also deals with optimization of simple structures. Optimization curves are obtained by varying the dimensions (or proportions) of the structure concerned. Finally, the dissertation also describes the possibility of making initial design decisions relating to dimensions (or proportions), using plots of optimization and plots of aesthetic preferences.