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Journal Cover   Engineer : Journal of the Institution of Engineers, Sri Lanka
  This is an Open Access Journal Open Access journal
   ISSN (Print) 1800-1122
   Published by Sri Lanka Journals Online Homepage  [45 journals]
  • Streamflow, Suspended Solids, and Turbidity Characteristics of the Gin
           River, Sri Lanka

    • Authors: T. N. Wickramaarachchi, H. Ishidaira, T. M. N. Wijayaratna
      Abstract: Human induced impacts on the river systems result in decrease in water quality, which is generally reflected by an increase of particulate matter in rivers. Turbidity and suspended solids are part of physical and aesthetic parameters and good indicators of other pollutants that are carried as sediment in suspension. Study objectives were to define the relation between turbidity and total suspended solid (TSS) concentration in Gin river at Baddegama (6°11'23" N, 80°11'53" E) in developing an estimation technique for TSS load, and to reveal how turbidity and TSS load vary with the streamflow. Linear regression model developed between turbidity and TSS concentration showed strong positive correlation (R2 = 0.98). Results strongly suggest turbidity is a suitable monitoring parameter for TSS, where TSS evaluation is crucial when logistical and financial constraints make TSS sampling impractical. Mean daily TSS loads in the Gin river at Baddegama during 2000-2009 were modeled in the study using load-discharge rating curve for estimating constituent loads in rivers. Relatively strong relationship (R2 = 0.85) was observed between the rating curve estimated and observed TSS loads. Estimated TSS loads were having substantial temporal variation and generally peaked in May and October, coinciding with the high flows. Turbidity which ranged between 2.3 NTU (Nephelometric Turbidity Units) and 195 NTU significantly exceeded the maximum permissible limits of the water quality standards set for the potable water as well the inland waters of Sri Lanka. Since there was no specific water quality standards developed for TSS in Sri Lanka to compare with the present values, TSS concentrations were compared with the permissible total solid levels. TSS concentrations which ranged between 2.4 mg/l and 204 mg/l were well below the maximum permissible total solid level cited in the Sri Lanka standards for potable water. Understanding on this turbidity and TSS characteristics in Gin river flow might be useful for water managers and planners to adjust operations accordingly at water treatment plants.
      DOI : ENGINEER, Vol. 46, No.04, pp. 43-51, 2013

      PubDate: 2014-04-08
      Issue No: Vol. 46 (2014)
  • Peak Electricity Demand Prediction Model for Sri Lanka Power System

    • Authors: G.V. Buddhika De Silva, Lalith A. Samaliarachchi
      Abstract: Accurate prediction of daily peak electricity demand is a requirement for service reliability, system stability and operating performance of a power system in the field of electrical engineering. This has now become a very important factor for Sri Lanka power system, since the available power plants are to be dispatched in an economical and reliable manner especially during the peak demand period of the chronological load profile. Therefore the prediction of next day peak electricity demand to an acceptable accuracy is useful for the system control centre (SCC) of the Ceylon Electricity Board (CEB). However, presently the unit commitment to meet the next day peak electricity demand is being mostly done by the system control engineers based on their past experience in the field of operation with respect to the day, period and other factors. This research paper carefully identifies sensitive elements which affect the daily peak demand of Sri Lanka power system and develop two forecasting models, namely linear statistical “Multiple Regression” and feed forward “Artificial Neural Network”. Both models were developed and fine-tuned using recorded peak demands of Sri Lanka power system from year 2008 to 2011 taken from the SCC of CEB and tested for the calendar year 2012 and also for the first few months of 2013. Artificial Neural Network model was found to be the best fit model for the prediction of daily peak demand of Sri Lanka power system with the lowest Mean Absolute Percentage Error (MAPE).
      DOI : ENGINEER, Vol. 46, No.04, pp. 53-60, 2013
      PubDate: 2014-04-08
      Issue No: Vol. 46 (2014)
  • Floating Wetlands for Management of Algal Washout from Waste Stabilization
           Pond Effluent: Case Study at Hikkaduwa Waste Stabilization Ponds

    • Authors: Sujatha Kalubowila, Mahesh Jayaweera, Chandrika M. Nanayakkara, Dhanesh N. De S. Gunatilleke
      Abstract: Waste stabilization ponds are advantageous waste water treatment processes, especially for developing countries. Nevertheless, in spite of the well known advantages of the implementation of the stabilization pond system, the effluent of this system has a significant amount of algae and high nutrients. Disposing this effluent with high contents algae and nutrients to the receiving waters can hinder the water reuse for a wide range of different applications, it is essential to look for a post treatment method that can provide considerable removal of algae, nutrients and organic matter from the effluent and at the same time, assure that the treatment system as a whole will maintain the advantages of the pond treatment processes. In this context, this research study was planned and intended to introduce a floating treatment wetland in which water hyacinth plants (Eichhornia crassipes) were used as macrophyte or vegetation in the part of the maturation pond area to control algae and nutrients in the effluent. With the application of the floating wetland the removal efficiencies were found to have increased in the maturation pond in terms of BOD and COD from 13.3% to 62.9% and 13.6% to 57.5%, respectively. In the case of TP and TN there were no significant reductions achieved prior to the establishment of the wetland but, reductions of 74.8% for TP and 55.8% for TN were achieved since the establishment of floating wetland. It was also possible to achieve a reduction of algal cell densities of 900 units/ml to zero unit/ml for the algal species of Spirulina and for Oscillatoria, the reduction was from 290 units/ml to 0 units/ml. In case of Chlorella and Pandorina, density reductions were 830,000 units/ml to 68,000 units/ml and 4300 units/ml to 280 units/ml respectively. Accordingly, the reduction efficiencies for Spirulina, Oscilltoria, Chlorella and Pandorina were reported to be improved from 31.8% to 100% and 4.5% to 100%, 34.2% to 91.8% and 42.2% to 93.5%, respectively. Application of this research can therefore be possible to polish waste stabilization pond effluent economically in order to re-use for various beneficial uses except potable use.
      DOI : ENGINEER, Vol. 46, No.04, pp. 63-74, 2013
      PubDate: 2014-04-08
      Issue No: Vol. 46 (2014)
  • Investigation on Efficiency of Repairing and Retrofitting Methods for
           Chloride induced Corrosion of Reinforced Concrete Structures

    • Authors: B.H.J. Pushpakumara, Sudhira De Silva, G.H.M.J. Subashi De Silva
      Abstract: The corrosion of steel reinforcement bars is one of the major deterioration mechanisms of Reinforced Concrete (RC) structures. Once the corrosion signs appear on the concrete surface, it may be too late to prevent further corrosion. As a result, service life of RC structures would be reduced. Use of repairing and retrofitting methods at the appropriate time will contribute enormous saving of country budget, which is required for re-construction. This paper presents an experimental investigation of repairing and retrofitting methods for the RC structures corroded due to chloride attack. As repairing methods for delaminated areas of corroded RC structures, Fly Ash (FA) and Silica Fume (SF) mixed mortars were developed and their performances were evaluated. As retrofitting methods, Cathodic Protection (CP) and Electrochemical Chloride Extraction (ECE) were conducted. ECE method is similar to CP method except the anode was covered by Ca(OH)2 layer. RC beams with concrete of Grade 20 and reinforcement bars of 16 mm diameter were cast. Efficiency of both repairing and retrofitting methods was evaluated by measuring free and total chloride ion concentration and rust production. Efficiency of repairing and retrofitting methods was further evaluated by measuring resistivity and Rapid Chloride Permeability Test (RCPT) and current measurement, respectively. FA mixed mortar reduces the total chloride ion concentration near embedded steel reinforcement bars in concrete by 40% while SF mixed mortar reduces 25% compared to OPC mortar. FA and SF mixed mortars prevent the corrosion process by minimizing the diffusion of chloride ions into concrete. It was found that CP method removed around 49% of total Cl- while ECE method removed around 69% of total Cl- near the steel reinforcement of RC beams. Removing of total Cl- by ECE is grater (in 20%) than that of by CP method. Chloride contaminated concrete that is still sound can be retrofitted by using CP and ECE methods and the spalled and detached concrete can effectively be repaired by using FA mixed mortars.
      DOI : ENGINEER, Vol. 46, No.04, pp. 19-30, 2013
      PubDate: 2014-04-07
      Issue No: Vol. 46 (2014)
  • Potential and Viability of Rice Husk Based Power Generation in Sri Lanka

    • Authors: Asanka S. Rodrigo, Shantha Perera
      Abstract: Due to intense fuel dependency on energy production in the world, cost of energy is now heavily depends on the prices of fossil fuels. Most of the countries in the world are suffering due to this and Sri Lanka is no exception. It is in this context promotion of biomass, as a renewable source, is so vital to the country. Rice being the staple food of the country as well as the crop with highest land area under cultivation, rice husk (RH) generated in paddy processing was found to have a significant potential in power generation. This paper investigates the possibility of using rice husk as a viable source of power generation in Sri Lanka. It is clearly seen that there is a significant potential in the districts of Ampara, Polonnaruwa, Anuradhapura and Kurunegala for power generation using rice husk. It was found that 30% of excess RH can be exploited for power generation with an annual energy potential of 180 GWh. This potential can be exploited by (1) Commercial scale RH power plants, (2) Small scale power plants under net metering scheme and (3) Off grid RH power plants.
      DOI : ENGINEER, Vol. 46, No.04, pp. 9-17, 2013
      PubDate: 2014-04-07
      Issue No: Vol. 46 (2014)
  • From the Editor

    • Authors: T. M. Pallewatta
      DOI : ENGINEER, Vol. 46, No.04, pp. III, 2013
      PubDate: 2014-04-07
      Issue No: Vol. 46 (2014)
  • Factors Influencing the Service Life of Buildings

    • Authors: W.P.S. Dias
      Abstract: The service life of a building depends mainly on its chief structural materials and the environment it is placed in. This paper collates the evidence from condition surveys conducted on some buildings with ages of up to 125 years set in a humid tropical environment, and seeks to arrive at some generalizations. Load bearing masonry walls and timber floors had performed well, as had exposed steel sections that were well maintained. Buildings with such elements could be expected to last well beyond the ‘normal’ design life of 60 years. If a reinforced concrete building had been exposed to a chloride source, major repairs were required after just half this design life. Carbonation depth was found to broadly obey a correlation with the square root of time. However, it is shown that both depths of carbonation and surface chloride levels can vary considerably in different parts of the same building. These findings have direct implications for both construction (in the choice of materials) and inspection (with respect to sampling and use of multiple test methods).
      DOI : ENGINEER, Vol. 46, No.04, pp. 1-7, 2013
      PubDate: 2014-04-07
      Issue No: Vol. 46 (2014)
  • Productivity in Construction-A Critical Review of Research

    • Authors: D. A. R. Dolage, P. Chan
      Abstract: The aim is to bring a fresh perspective to the construction productivity research agenda, which is congruent with the new demands in the construction industry and its ever changing nature. The articles which had ‘construction productivity’ as a keyword in the abstract, and were published in each of the three journals (JCEM, CEM and IJP) from the earliest year that the articles had been uploaded to the respective official website of each journal were identified. Out of 5862 articles searched, only 121 articles fulfilled the selection criteria, the titles of which were examined. The past decade has witnessed the continuation of the same relentless research interest in productivity studies. The findings revealed that, in the studies: five types of productivity have been examined; five data collection methods have been deployed; research objects can be classified under seven categories. The research objects in a high number of studies are devoted to ‘measurement of productivity’ and ‘examining the casual relationships with productivity’. The study ascertained that the main drawbacks of past productivity studies are the strong empirical inclination of methodologies adopted and the overwhelming positivist approach to examining productivity issues. The absence of follow-up studies to investigate the validity of productivity measurement techniques and the models and to test the claims made in productivity improvement studies, is a striking feature. Another impressive finding is the lack of scholarly attention to incorporate blue-collar worker perspective, employee involvement, and social dimension into productivity research.
      DOI : ENGINEER, Vol. 46, No.04, pp. 31-42, 2013
      PubDate: 2014-04-07
      Issue No: Vol. 46 (2014)
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