Engineer : Journal of the Institution of Engineers, Sri Lanka
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Open Access journal
ISSN (Print) 1800-1122
Published by Sri Lanka Journals Online [48 journals]
- Determination of Optimum Nominal Aggregate Size for Single Surface
Abstract: Surface dressings can be used as a successful road maintenance activity if carried out properly. One of the main decisions to be taken in designing a surface dressing in road maintenance is the selection of appropriate aggregate size. Improper selection could tarnish the performance of a surface dressing. The aim of this study is to find the optimum size of aggregate for a single surface dressing, especially in Sri Lankan Macadam roads. General size of aggregate for a particular surface dressing could be found using two parameters, commercial traffic volume on road and surface hardness of the road based on many available highway literature. But the aggregate sizes selected in above simple method have shown inconsistent results in Sri Lankan roads. Therefore tests were carried out to find the most appropriate aggregate size for the surface dressings in medium to low traffic Macadam roads in maintenance operations.
Three most suitable nominal sizes of aggregates were selected using commercial traffic volume and the road surface hardness to begin the tests. These three sizes of aggregates were used to carry out three different surface dressings in the same road but in different stretches. Binder type were kept constant and binder rate was changed according to the aggregate size. The performances of these three surface dressings were evaluated by measuring aggregate removal rate and skid resistance. Digital photographs of demarcated locations in surface dressings of different aggregate sizes were taken at pre determined time intervals. .The numbers of aggregate were counted in each photo after certain time intervals up to 12 weeks and using this data, the behavior of each surface dressing over a period of time was studied. The aggregate size that could keep most of aggregate intact in its dressing after a certain time period would be a more durable chip size.
The next aspect of checking performance of the dressing is the skid resistance. The techniques utilized to measure this value are Locked wheel test and Sand patch method. These tests were done after 12 weeks since the operation a sufficient enough to stabilize the dressing. The comparison of aggregate retention on road surface and the skid resistance after 12 weeks will give the short term performance of three aggregate sizes. It was found that 9.5mm aggregate size has better performance in aggregate retention and the 12.5mm size has better skid resistance. Published on 2016-06-16 00:00:00
- Cracking due to Temperature Gradient in Concrete
Abstract: Mass concrete is used in many projects related to the massive construction such as raft foundations, pile caps, thick beams, walls and dams. Since cement hydration is an exothermic reaction, the temperature rise within a large concrete mass can be quit high. As a result, significant tensile stresses and strains may be developed from the volume change associated with the increase and decrease of temperature within the mass concrete which will lead to crack the concrete. Cracks caused by thermal gradient may cause loss of structural integrity and monolithic action or shortening of service life of the structures. The objective of this research is to determine the thermal strain variation from arisen temperature data which in turn can be used to predict, whether the relevant concrete section is going to be cracked or not by comparing with tensile strain capacity values. Published on 2016-06-16 00:00:00
- Shakedown Analysis of Road Pavements - Application to Project Level and
Network Level Scenarios
Abstract: Shakedown behaviour of road pavements was investigated in laboratory controlled conditions using the Sydney University Pavement Testing Facility. Wheel loads lower than the shakedown load generated low permanent deformations for a larger number of load cycles in comparison with high permanent deformations for a lower number of load cycles for wheel loads higher than the shakedown load. Computer software was developed to calculate the shakedown limit using elastic stress distributions calculated with Sydney University's FLEA (Finite Layer Elastic Analysis) program. Case studies of shakedown theory to solve project level construction issues and remaining service life calculations at the network level are presented. Published on 2016-06-16 00:00:00
- From the Editor Vol. 43(4)
Abstract: No abstract available Published on 2016-07-16 00:00:00
- The Curious Case of the Khettarama Pitch
Abstract: During the Compaq Cup tournament in Sri Lanka in September 2009, the teams batting under lights at the R. Premadasa (Khettarama) Stadium pitch consistently found it very difficult to bat and thus lost matches. Many were of the view that the pitch was helping bowlers a lot more during the evening making it very unfair for the team batting second. This paper is based on the study which was carried out by the authors at the request of Sri Lanka Cricket (SLQ to investigate the behaviour of the R. Premadasa Stadium (Khettarama) pitch. The study aimed to find out if there was any truth to the above claim by conducting insitu bounce tests and collecting top-dressing samples from the pitch at regular time intervals. The test was conducted during the hours of a normal day/night One Day International match would be played at this stadium and match conditions were simulated as far as possible. The variation of bounce with time was then compared with the moisture variation through the course of duration of play to see whether there were correlations between the two. Further, a theoretical discussion based on unsaturated soil mechanics and soil science on the effect of these factors is also included for better understanding. Published on 2016-06-16 00:00:00
- Development of High Performance Automatic Voltage Stabilizer for
Abstract: The telecommunication industry in Sri Lanka is showing fast growth and expands services to their customers, especially during past decades, by increasing number of service providers with much competitive Tariffs. The main challenge of the service provider is to sustain with the competitive Tariff reductions and advancement of their services to customer doorstep demanding by the industry. Not like in other industry, the telecom customer is having the freedom to select any service provider by own decision without facing any monopoly or other influence by the industry. This automatically creates the industry to reduce their OPEX & CAPEX continually. The CAPEX is always increasing and the reduction possibility exists only with OPEX in the telecom industry.
Electricity contributes to the major portion of OPEX of remote telecom site operations. The electricity by means of Diesel Generator (DG) operation or Commercial supply (CEB/ LECO) is always a difficult facility in remotely operated telecommunication base stations. This is due to the nature of the location of the selected site and the quality of the nearest/ rural commercial supply. Due to this, the site needs to run with the DG in most of the period of the day or face with service outages due to interruptions of the electricity with huge OPEX and unexpected losses in income.
The main objective of this research project is to develop a system for automatic voltage regulation at remote telecommunication sites with customized features. The outcomes of this research will be a remarkable development in the telecom industry. We also supposed to share this knowledge with all the interesting parties to extend the benefits not only to the telecom service providers, but also to the customers by means of lowest tariffs. Published on 2016-06-16 00:00:00
- Factors Influencing the Duration of Road Construction Projects in Sri
Abstract: This study attempts to reveal the factors influencing the duration of road construction projects in Sri Lanka, and to identify how delays can be mitigated. The emphasis here is limited to study the Contractor's point of view. The main concern of the study is to identify the nature of the population (Road projects in Sri Lanka) using Statistical Inference. The other focusing areas are to identify Main Causes of Delay & Delay Diversification, and Delay Mitigation. This study defines the Percentage Delay parameter and the Relative Significance Index (RSI) model, which are the new concepts introduced by the author this study.
The preliminary data for this research have been collected through a literature review and a questionnaire survey targeted at local contractors of Road Construction. The collected data yields a high reliability coefficient, which is 90%.
This study reveals that the local road construction projects experience 56 % - 88 % of average time overrun compared to the original (planned) project duration. The findings further illustrate that the financial problems of the Owner as well as of the Contractor, is the most influencing factor causing delays in road construction projects in Sri Lanka. Published on 2016-06-16 00:00:00
- Analysis of Surface Flashover of 33kV Pin Type Insulators due to Saline
Abstract: Contamination-driven insulator failure is a problem that incessantly plagues distribution systems. Contamination levels can continue to grow unless abated by natural cleaning or if not taken measures to wash insulators at the distribution level in a preventative maintenance mode. In order to assess the pollution behavior, 33kV pin type insulator was selected as a sample insulator and been subjected for natural pollution at three selected localities (zone 1, 2 and 3) for considerable period. The naturally polluted insulators have been subjected for conductivity test and by which the equivalent salt deposit density (ESDD) is calculated. Subsequently, artificially contaminated insulators of different pollution severities were tested for power frequency and impulse test in the High Voltage Laboratory of University of Moratuwa. Finally, it is recommended that insulators in Zone 1 have to be treated after 8 months from the date of last treatment and those in Zone 2 & 3 to be treated after 18 months under preventive maintenance to get away from flashover. It is also recommended to review the required specific creepage distance (SCD) of insulators installed in non-polluted areas due to the fact that the current practice of insulators placement in most of the places are with SCD of 25mm/kV which is recommended for high polluted zones as per IEC regulation. Published on 2016-06-16 00:00:00
- From the Editor Vol. 49(2)
Abstract: No abstract available Published on 2016-06-16 00:00:00
- A Methodology to Develop a Distribution Transformer Model for Transient
Abstract: Transformers are some of the expensive components of a distribution network. Records from the Ceylon Electricity Board (CEB) indicate that a considerable number of failures of these transformers are caused by lightning surges. Transformer failures incur huge costs to utility suppliers like CEB.Thus the behaviour of distribution transformers under transient conditions needs to be studied and for this a transformer model is very much essential. With the help of such a model, the behaviour of distribution transformers when subjected to lightning surges can be studied.In this paper, a methodology is presented to develop a model to represent a distribution transformer under transient conditions. The validation of the model is illustrated by the calculation of parameters based on a 160 kVA, 33/0.415 kV, three phase distribution transformer. The model is simulated using PSCAD software and the output is obtained when the standard lightning waveform and chopped surge waveforms are input to the model. In order to validate the developed model, the output voltage distribution along the transformer winding is observed and compared with the results of an experiment presented in a research publication . Published on 2016-06-16 00:00:00