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Browsing Journals and Magazines by Faculty "Engineering"

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    item: Conference-Abstract
    Earthquake Performance of free Standing four Legged Greenfield Towers
    Gunathilaka, AMLN; Lewangamage, CS; Jayasinghe, MTR;
    Telecommunication/broadcasting towers play a vital role in telecommunication and broadcasting sectors by facilitating wireless data and signal transmissions. The failure of a tower especially under a disaster situation such as earthquake is a major concern mainly in two ways. One is the failure of communication/broadcasting facilities which will become a major setback to carry out rescue and other essential operations during a disaster while failure of a tower will itself cause a considerable economic loss as well as damages to human life since these are tall giant structures in most of the cases. Presently, a strong dialogue is going on amongst the professionals regarding the seismic condition of our country with the reported earth tremors in recent times. Hence, evaluating the structural performance of existing telecommunication/ broadcasting towers under seismic loads is utmost important since almost all existing towers have not been designed considering seismic forces due to traditional belief that Sri Lanka will not be subjected to earthquakes of appreciable magnitudes. Considering the above situation, assessment of structural performance of existing towers (which were not initially designed considering earthquake loading) under possible earthquake loading with different analytical techniques was selected as main objective of this study. Accordingly, behaviour of existing four legged Greenfield towers under seismic loading using ANSI/TIA-222-G tower design code was studied and results, observations and conclusions based on this analysis are presented.
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    item: Conference-Abstract
    Enhancement of engineering characteristics of peaty clay due to mixing with cement
    Saputhantiri, DR; Kulathilaka, SAS
    Thick layers of soft peaty clay encountered in recent infrastructure development projects in Sri Lanka had been improved mainly by different techniques of pre-consolidation. Alternatively, if peaty clay is mixed in situ with a binder, such as cement, apozzolonic reaction can be induced causing a fundamental change in microstructure. Greater improvement of strength and stiffness would be achieved more rapidly than with pre-consolidation. Samples of peaty clay obtained from the Southern Transport Development Project were mixed with 15% and 20% of cement by wet weight and the mix was allowed to harden. A surcharge was applied by a special loading arrangement to simulate the overburden pressure under which it will harden in the field. Improvements achieved in strength and stiffness of treated peat were assessed by conducting consolidation tests and unconsolidated undrained triaxial shear tests. The results indicated that significant improvements were achieved in the undrained shear strength and primary and secondary consolidation characteristics. Improvements achieved in secondary consolidation ,characteristics were more significant. Micrographs obtained through Scanning Electron Microscopes (SEM) illustrated the micro structural changes taken place in the peaty clay due to mixing with peat.
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    Liquefaction potential in Sri Lanka - preparing a liquefaction hazard map using geotechnical investigation data
    Kumarasiri, HC; De Silva, LIN; Abayakoon, SBS;
    Soil Liquefaction is a process, where granular soils below the ground water table temporarily lose their strength due to cyclic loading created by an earthquake. Liquefied soil behaves as a viscous fluid rather than a solid. During liquefaction, porewater pressure is suddenly increased, forcing the soil particles to suspend in water. As a result, the buildings, utility services, natural substances and other structures become unusable causing severe damages. Hence, as some tremors have been reported in and around Sri Lanka [2,3] and even a minor earthquake can cause soil liquefaction, it is important to consider possible mitigation measures prepare for liquefaction. In Sri Lanka, it is rare to find historical data of liquefaction related incidents. Recent studies demonstrated that there is a potential for liquefaction in some places of the island [5]. This could be evaluated by analyzing the basic geotechnical investigation data, according to the simplified procedure proposed by Seed and Idriss (1971). This paper proposes a procedure to prepare a liquefaction hazard map for Sri Lanka by identifying the hazard zones using an extensive geotechnical investigation data base. In this analysis 384 locations were identified as susceptible for liquefaction out of 3282 locations analyzed. It is to be noted that the research has given a special attention to the variation of ground water table and the maximum possible ground accelerations.
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    item: Thesis-Abstract
    Measures to reduce transformer failures in the distribution network of CEB
    (2014-08-01) Wijekoon, VB; Perera, HYR; Wijekoon, HM
    Ceylon Electricity Board (CEB) has many transformer installations in its distribution network, with their capacities ranging from 100 kVA to 1000 kVA. The latest transformer designs are very much simplified and optimized. Due to the vast spread in the distribution network and practical constraints in employing high end protective devices, these transformers more frequently undergo adverse impacts imposed by the condition of the network and by the nature. These transformers are nowadays manufactured to operate almost without supervision. A high failure rate of nearly 3% per year (out of approximately 20,000 installed transformers) could be observed. When added up the cost due to loss of transformers, the overall loss becomes nearly one billion rupees per year. Although most of the causes contributing for these failures are thought beyond our control, it is investigated and found that this failure rate can be drastically reduced by merely following better erection practices. This report discusses many causes for distribution transformer failures and elaborates on measures that can be adopted for reducing transformer failures, mainly through proper erection practices. Existing transformer installations are studied and analyzed to see whether the present auxiliary gear used, lead connecting methods followed and earthling done are acceptable for proper functioning of transformers. It is analyzed and shown that the earthling method practiced presently on MV transformer installations is not effective. A research which has been initiated to determine an improved earthling system is introduced and discussed in this report. Conclusions of this research would be arrived after a careful study. Studies are carried out to determine the most probable lightning pattern in Sri Lanka and their effects on the distribution network, especially on transformers. A transient waveform simulation is done to observe the voltage stresses exerted on transformers for few selected installation arrangements. This is further expanded to carry out a sensitivity analysis to observe the behavior of voltage stresses under different types of lightning surges. A better installation practice is thereby proposed.
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    Prototype implementation of an islanding detection relay based on pattern classification of current and voltage transients
    Lidula, NWA; Rajapakse, AD; Pham, JP; Denboer, N
    A prototype islanding detection relay, which uses decision tree classifier to categorize the transient generating events as ‘islanding’ or ‘non-islanding’ was implemented and tested. It consisted of two basic stages of signal processing to extract the required feature vectors for the classification. The first stage involved signal filtering and in the second stage signals were processed by rectifying, summing, and lowpass filtering to get the energy content in the three phases during a selected time-frame. A simple radial medium voltage distribution system having a single distributed generator was simulated in PSCAD/EMTDC to obtain the transient waveforms, and the performance of the relay was tested with signals generated using an RTP real-time waveform playback instrument. The experimental results showed high accuracy in detecting islanding events within a response time of less than two cycles. The proposed relay can be implemented with a very low cost and is simple in construction. Therefore, this could be an acceptable low cost substitute for the expensive and complex transfer trip schemes, which are commonly in use with the distributed generation.