Browsing by Author "Hettiarachchi, MTP"

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item: Thesis-Abstract
A study of built - up timber structural elements
Mohanathevan, S; Hettiarachchi, MTP
Code on timber design CBS 5268 Part 2, 1991) gives no provisions for the design of layered braced and box timber columns except spaced timber columns. Very little information is available about these in the literature on timber structures. This paper provides procedure for determining the axial load capacity of mechanically connected built-up columns, such as layered columns, spaced columns, braced columns and box columns. In addition to that, it gives information about nail connection details and arrangement. Mainly concentrated on built-up timber columns made up with mechanical connection as it could be done locally. The theoretical development takes into account the effect of columns stability and effectiveness of the shear transfer. The experimental results obtained by under graduate students are compared with theoretical predictions. Conclusions are drawn with regards to the suitability of the design methods for built up timber columns made by nailed connections.
item: Conference-Full-text
Analysis of storm water drainage system at park road in Colombo using storm water management model (SWMM)
(Department of Civil Engineering, University of Moratuwa, 2015) Nandharathne, ABDT; Wijayaratna, TMN; Hettiarachchi, MTP
Colombo city is the main commercial and administrative hub of Sri Lanka. The city is frequently subjected to flooding during rainy seasons which disturb day to day routines. The existing drainage system is not sufficient for the current storm water demand. In this study, the existing storm water drainage system in Park road area in Colombo 5 is analyzed using Storm Water Management Model (SWMM). Apart from simulating the existing storm water drainage system in the area, the present study identifies the possible reasons for the flooding and introduces remedial measures using the Storm Water Management Model (SWMM).
item: Thesis-Full-text
Application of Eurocode 5 recommendations to the bolted joints of Sri Lankan timber species
Nawagamuwa, AD; Hettiarachchi, MTP
Eurocode 5 "Common Unified Rules for Timber Structures" is the latest structural design code, which provides guidelines for structural timber design. Eurocode 5 procedures for the design of bolted and nailed timber joints are based on an analytical model, which developed by Johansen in 1949. This model is often referred to as European Yield Model (EYM) and provides more reliable design procedure than older empirical models. This thesis provides information of the research work, which was carried out at the University of Moratuwa to check the applicability of Eurocode 5 design procedure to bolted timber joints made from local timber species. The test programme was conducted using two local timber species and three bolt diameters, which are commonly used in the construction industry, with wider range of joint geometries while most of past research were conducted using only one or two joint geometries. Based on the results obtained from this test programme, it was possible to propose a new model for the determination of embedment strength of local timber species and a modification factor, which is determined based on the joint geometry. This modification factor modifies the Eurocode 5 predictions for the strength of bolted timber joints of different geometry to reasonably acceptable conservative values. Reasons and the methodology of this research programme are explained briefly in the first chapter while the second chapter describes, in detail, the background for this research programme. From the third chapter the reader is able to obtain much information on Eurocode 5 and European Yield Model, which are found from a thorough literature survey carried out on the available research papers, journals and textbooks. Scheduled experimental programme adopted according to the recommendations of previous research and guidelines obtained from the literature survey is provided in Chapter 4. Chapters 5 and 6 provide the results obtained from embedment strength test programme and joint strength test programme and the analysis of those results. Conclusions based on the analysis and recommendations for further works are provided in chapter 7.
item: Conference-Full-text
Assessment of groundwater resource utilization in wet and dry zone aquifers in Sri Lanka and quantifying recharge losses due to urbanization and land-use change
(Department of Civil Engineering, University of Moratuwa, 2016-12) Dilhara, MAAR; Rajapakse, RLHL; Hettiarachchi, MTP
In Sri Lanka, almost all people have either direct or indirect connection to the groundwater resources. Rapid urbanization, deforestation and land use changes have recently incurred adverse impacts on groundwater recharge, leading to groundwater table decline and drying up of wells. A quantitative analysis of groundwater utilization and recharge loss due to urbanization and subsequent land use change was carried out in this research. Attanagaluoya (Dunamale catchment) and Kirindioyabasin (Thanamalwila catchment) were the study areas selected in wet and dry zones, respectively. The 4-parameter “abcd” monthly water balance model was developed to be compatible with the research objectives based on the gathered and simulated stream flow, groundwater and recharge data and the calibrated and validated model was then used in further analyses and quantitative assessment of recharge loss. The results indicate severe impact on groundwater recharge in dry zone in the future. Further, sustainable groundwater management and proper land use policies to overcome groundwater recharge loss in both wet and dry zones were proposed based on scenario analyses.
item: SRC-Report
Behaviour of built up nailed timber box beams
Hettiarachchi, MTP
Timber is unique among construction materials in that it is a renewable resource. It has an added advantage that the manufacture of timber from the tree consumes less energy and causes less pollution when compared to other construction materials. However, today, timber is increasingly becoming a scarce resource due to indiscriminate felling of trees. An endless supply of timber and timber based materials can be ensured with the adoption of prudent forestry management techniques and using timber with care so that its full potential is realised. The size of a tree determines the maximum dimensions of the timber section that are produced. Large cross sections of timber are difficult to obtain and are very costly. Adopting the familiar structural principle of the I beam (a pair of flanges separated by a web) as the most efficient cross sectional profile for bending action, timber and plywood have been combined to build up beams that span distances that solid timber beams alone cannot.
item: Conference-Abstract
Behaviour of nailed timber box beams
Hettiarachchi, MTP
Experimental investigations on nailed built up timber box beams of different cross sectional profiles in which the flanges and webs are both entirely of timber are carried out with the objective of understanding the behaviour of the different nailed built up beam configurations and identify their potential as an alternative to the use of solid timber beams. In particular the effect of web thickness, overall depth and shape of flange on the load carrying capacity and flexural rigidity of timber box beams are investigated. Timber beams consisting of webs of 25 mm thickness and overall depth of 225 mm are the most cost effective. The profile of the flange does not have a significant effect on either the load carrying capacity or flexural rigidity. It is observed that flexural rigidity and load capacity are better correlated with the second moment of area and section modulus of only the webs of the box beam rather than that of the entire box beam.
item: Conference-Full-text
Behaviour of nailed timber box beams
(2015-08-03) Hettiarachchi, MTP
Experimental investigations on nailed built up timber box beams of different cross sectional profiles in which the flanges and webs are both entirely of timber are carried out with the objective of understanding the behaviour of the different nailed built up beam configurations and identify their potential as an alternative to the use of solid timber beams. In particular the effect of web thickness, overall depth and shape of flange on the load carrying capacity and flexural rigidity of timber box beams are investigated. Timber beams consisting of webs of 25 mm thickness and overall depth of 225 mm are the most cost effective. The profile of the flange does not have a significant effect on either the load carrying capacity or flexural rigidity. It is observed that flexural rigidity and load capacity are better correlated with the second moment of area and section modulus of only the webs of the box beam rather than that of the entire box beam.
item: Thesis-Full-text
Bolted end plate beam to column connections – are they semi rigid?
Kalyani, P; Hettiarachchi, MTP
The most commonly used moment resisting connections are bolted end plate beam to column connections. Connections are usually designed as simple or continuous although the actual behavior is known to fall between these two extreme cases. The use of semi- continuous connection results substantial savings in steel weight of the overall construction. Extended endplate, Flush end plate and partial depth connections are the widely used type of connections in steel frame construction. To understand the real behavior of semi- continuous connection, full scale laboratory test is the most accurate approach, but it is time consuming and costly to undertake. Therefore other methods were developed to predict the capacity of connections. Thus, in this study 48 extended end plate and 48 flush end plate connections are analyzed to find the connection’s behavior with variations in bolt diameter, end plate thickness, and grade (4.6/8.8) and bolt gauge length. A method proposed by Steel Construction Institute (SCI) is taken into account for analyzing. The analyzed connections are classified based on strength and stiffness.
item: Conference-Full-text
Civil Engineering Research Symposium 2015 (Pre Text)
(Department of Civil Engineering, 2015) Hettiarachchi, MTP
item: Conference-Full-text
Comparative study on strengthening methods of steel towers
(Department of Civil Engineering, University of Moratuwa, 2014-03) Ganadhiepan, G; Baskaran, K; Hettiarachchi, MTP
Steel towers are widely used in the telecommunication and power transmission sectors. Failure of these towers causes direct and indirect losses and disruption to the services provided by those towers. As a result, industries and general public face difficulties and the productivity of the country also gets affected. Considerable number of tower failures has taken place in both power transmission and telecommunication sectors of Sri Lanka in the recent past but only a little amount of studies has been done so far. Testing at least a tower in a transmission line is mandatory in the power transmission sector of Sri Lanka. Generally these tests are carried out at the Structural Engineering Research Centre in Chennai. It has been observed that several towers fail prematurely under normal loading conditions during full scale tests, indicating lack of strength of towers. The objectives of this study are analysing tested towers using finite element method and comparatively studying different techniques of strengthening of towers. A general purpose finite element analysis program SAP2000 was used for the modelling and analysis of towers. Finite element model of a tower which has been tested to full scale was developed and validated in SAP2000. Then different methods of strengthening were carried out to the validated model to comparatively study the effect of each method on the strength of the tower. The findings are presented in this paper.
item: Conference-Full-text
Comparison of built up timber beams with timber trusses
(Department of Civil Engineering, University of Moratuwa, 2016-12) Perera, KDN; Hettiarachchi, MTP; Hettiarachchi, MTP
The following work is based on a comparison of timber box beams with parallel chorded timber trusses. Box type built up box beams have been adopted based on past research conducted in the Sri Lankan context. Two types of parallel chorded trusses have been compared with a box beam, where the trusses are of the same overall dimensions. Built up box timber beams are found to be the most effective and efficient solution compared to parallel chorded timber trusses of same depth as an alternative for heavy timber beams. Since the serviceability limit state governs the design criteria, load carrying capacities at allowable deflection were concerned. Built up box beam performed 2 to 2.5 times when compared to the Pratt and Warren trusses in terms of load carrying capacity per unit timber cost at allowable deflection.
item: Conference-Full-text
Comparison of design of stone columns by limit equilibrium and finite element methods
(Department of Civil Engineering, University of Moratuwa, 2016-12) Perera, WLDHA; Kulathilaka, SAS; Hettiarachchi, MTP
Use of stone columns is a ground improvement technique that can be applied when high embankments are to be constructed on thick layers of soft soils. Stone columns installed in an appropriate pattern, reinforce the soft soil enhancing the shear strength and reducing the settlements. There are several methods for the analysis and design of stone columns. These designs come up with a factor of safety, which cannot be verified in the field. Comparison of Factor of Safety computed with different approaches will be useful in optimizing the design procedures. Designs done with limit equilibrium approach and finite element approach are compared in this research. GEOSLOPE - SLOPE/W software was used for the limit equilibrium approach and PLAXIS 2D software was used for the finite element analysis.
item: Conference-Full-text
Comparison of different types of pedestrian paving materials
(Department of Civil Engineering, University of Moratuwa, 2015-10) Galabada, GH; Karunathilaka, KMHC; Halwatura, RU; Hettiarachchi, MTP
The need for selecting correct material for the pedestrian paving is greater than ever before. Due to increasing number of pavements constructed in urban areas the climate conditions of cities are changing into unfriendly levels. With the escalation of prices of the conventional paving materials (asphalt, concrete) and sustainability concepts designers are on the verge of using alternative materials for the road construction which brings sustainable and eco-friendly, more energy efficient living conditions. In this research different types of paving materials are compared through a questionnaire survey, thermal performance test and a cost comparison. The results of the study indicate that the use of clay paving block pavement is more suitable than the conventional pedestrian paving methods. The low cost, the ability of accommodating and maintaining utility services, thermal comfort, aesthetic appearance and environmentally friendly behavior and user satisfaction can be highlighted as the key advantages of clay paving blocks.
item: Thesis-Abstract
Computerized optimization of the base width of transmission towers in Sri Lanka
(2015-02-22) Ganeshwaran, R; Hettiarachchi, MTP; Baskaran, K
Transmission line towers were mainly used in electrification works in all over the world. Optimization of base width of the transmission towers becomes necessary in order to reduce the cost and to avoid public objection. The use of narrow width tower becomes essential, as the land value appreciates drastically in Sri Lanka. This research is to design the transmission towers with reduced base width to minimize the coverage land with optimum weight and adequate strength. There were number of models selected with 14.2m base width and analyzed by reducing the width in steps from 1m to 3.2m. For this purpose computerized model analysis software named PLS Tower was used. Accordingly cost analysis was carried out for different steel prices and the cost of land. As per this study Optimum base width of 6.2m was found considering both the land & steel price. When compared with the towers used in Sri Lanka, it was found that the narrow width towers designed from this study showed a considerable amount of saving in cost and favourable impact on environmental issues.
item: Thesis-Abstract
Computerized optimization of the based width of transmission towers in Sri Lanka
(2015-06-24) Ganeshwaran, R; Hettiarachchi, MTP
Transmission line towers were mainly used in electrification works in all over the world. Optimization of base width of the transmission towers becomes necessary in order to reduce the cost and to avoid public objection. The use of narrow width tower becomes essential, as the land value appreciates drastically in Sri Lanka. This research is to design the transmission towers with reduced base width to minimize the coverage land with optimum weight and adequate strength. There were number of models selected with 14.2m base width and analyzed by reducing the width in steps from 1m to 3.2m. For this purpose computerized model analysis software named PLS Tower was used. Accordingly cost analysis was carried out for different steel prices and the cost of land. As per this study Optimum base width of 6.2m was found considering both the land & steel price. When compared with the towers used in Sri Lanka, it was found that the narrow width towers designed from this study showed a considerable amount of saving in cost and favorable impact on environmental issues.
item: Conference-Full-text
Condition assessment of steel bridges in Sri Lanka
(Department of Civil Engineering, University of Moratuwa, 2014-03) Chathuranga, KADK; Lewanagamage, CS; Hettiarachchi, MTP
The majority of steel bridges in Sri Lanka have been built more than 100 years ago. Most bridges have been subjected to changes such as deterioration due to corrosion, mechanical damage due to fatigue and repair due to maintenance. Therefore condition evaluation of such bridges is vital to ensure public safety. This paper presents condition assessment of selected steel bridges in Kaluthara district. The task is pursued through visual observations. Two mathematical models have been developed in this research to evaluate the condition of bridges. The Analytical Hierarchy Process was applied to obtain the priority vector of bridge elements and important factor of bridge elementswere used to obtain the overall bridge condition index. The modified overall bridge condition index is employed to assess the bridge condition. The results obtained from four selected steel bridges are presented in this paper.
item: Thesis-Abstract
Corrosion prevention of stell structures for Sri Lanka Author Premachandrasiri, W.N.
(2015-07-07) Premachandrasiri, WN; Hettiarachchi, MTP
Sri Lanka has made a significant development in the design and construction sector during the last 10 years. The use of steel is one of the governing construction materials in the industries. One of the major concerns of existing steel structures is the durability. Corrosion and deterioration have become major challenges in the lifetime of the structure, as it is one of the major public focuses on the structures. Standards are intended to assist engineers and corrosion experts in adopting best practice in corrosion protection of structural steel at new constructions with proper identification of an actual exposure. There are six environmental corrosivity categories according to BS ISO 12944 as C1, C2 C3, C4, C5 and C5 –M. Those are according to BS standard and they should be adapted for Sri Lanka. In this research environmental corrosivity category of SC1, SC2, SC3 and SC4 are classified for Sri Lanka considering corrosion affecting factors temperature, rainfall, coastal region and industrial zones. A field survey was carried out in different locations of the structure in the country to identify the pattern of corrosion according to variation of corrosion affecting factors. Among the methods used to clean the surface of the steel before applying corrosion protection, sand blasting cleans best. However, it cannot be carried out in every location due to environmental issues and equipment required. Steel surface is difficult to clean using light tools because temporary stabilized corroded layer on the steel surface. If we change this surface (Convert surface grade A to Surface grade B), the light tools can be used for the surface preparation. Therefore a new method is proposed to change this surface grade. Firstly, sea water is sprayed on to the surface to increase the rate of corrosion and left for a day for rust to appear. Then it is cleaned by fresh water and surface salinity level should be checked using salinity meter. Then the surface can be prepared using “Cup-Brush application” method without using sand blasting. By this method well cleaned surface can be obtained and then the surface protection primer is applied on it immediately. This surface protection primer type and primer and paint thickness should be defined according to environmental corrosivity category.
item: Conference-Full-text
Determination of permeability characteristics and SWCC of an unsaturated residual soils in Sri Lanka
(Department of Civil Engineering, University of Moratuwa, 2016-12) Karunasena, GKGM; Kulathilaka, SAS; Hettiarachchi, MTP
Sri Lankan residual soils are formed by weathering of the metamorphic parent rock. Failure in slopes made of such residual soils frequently occurs due to excessive rainfall. With the rain water infiltration, soil will gradually get into a saturated state loosing the matric suction. Sometimes perched water table could also develop. Therefore, with the rainfall, slopes that are stable in dry periods may be subjected to failure. Soil Water Characteristic Curves (SWCC) and knowledge of variation of permeability in unsaturated soil are essential to model this behavior and to devise a reliable early warning system which is in most demand in the present day context. This research project focuses on the development of the permeability function of an unsaturated residual soil in Sri Lanka. Permeability function for both wetting and drying phases were investigated. The method is based on continuously drying and wetting the soil sample while continuously monitoring the suction gradient and the change in soil mass.
item: Conference-Full-text
Determination of suitability of the limestone aggregates as coarse aggregate for concrete
(Department of Civil Engineering, University of Moratuwa, 2014-03) Perera, MUD; Dilrukshi, KGS; Hettiarachchi, MTP
The use of limestone in the construction industry has been increasing due to its potential as aggregate. Some of the benefits of limestone include good strength, low possibility of alkali-silica reaction and the decrease in drying shrinkage in concrete. In the northern part of the Sri Lanka, limestone is used as aggregate in concrete due to its availability'. The aim of this research is to observe, evaluate, compare and discuss general characteristics of the limestone aggregate in the northern part of Sri Lanka and check the suitability of the limestone as coarse aggregates in concrete. There are two different kinds of limestone there, namely Red limestone and white limestone. Then experiments are conducted for both kinds of limestone together with the normal coarse aggregates. The properties of density, water absorption, particle size distribution, Flakiness Index, Los Angeles Abrasion Value, Aggregate Impact Value, Aggregate Crushing Value and Soundness of the aggregate are observed. The results are compared with the properties of the coarse aggregates and then suitability of limestone aggregates is evaluated.
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.