Master of Engineering in Structural Engineering Design

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Browsing Master of Engineering in Structural Engineering Design by Subject "BRIDGES"

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    item: Thesis-Abstract
    Applicability of suspension bridges for transportation in rural areas in Sri Lanka
    Thrimavithana, RSK; Jayasinghe, MTR
    For the rapid economic development of rural villages in Sri Lanka the transportation facilities should be upgraded. In this context, one of the bottlenecks is the need of large number of bridges which is a costly item. Therefore the solution given at the moment is the provision of pedestrian suspension bridges, which can be used only for passengers. Almost all the suspension foot bridges available might not withstand dynamic forces such as wind induced dynamic forces and human induced dynamic forces. The biggest issue on these bridges is the safety. For these locations the development of a suspension bridge that can handle both human and cycles loads safely, will be a great advantage. These structures however are always lively with low stiffness, low mass, low damping and low natural frequencies./ A conceptual study has been carried out to investigate the dynamic characteristics of slender suspension foot bridges under human induced dynamic loads. As the first step, some places where suspension foot bridges are located were visited. While crossing the bridge, during the site visit it was felt that those existing bridges are not comfortable and identified as low safety. Different types of suspension bridges and different structural models were observed. Then existing suspension foot bridges were modeled using both software PROKON (V-2.1) and SAP 2000 (V9.3). Under the first step it was tried to introduce different modifications to existing bridges to satisfy comfort and more structural stability with safety. Since these bridges are having low structural factor of safeties, no modifications are allowed.
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    item: Thesis-Abstract
    Comparative analysis o n simply supported pre- stressed box beams in Sri Lankan highway bridges
    (2014-08-22) Jabbar, MARMA; Jayasinghe, MTR
    The National Road network of Sri Lanka consists of 4326 bridges. There are 365 bridges which Have the length more than 30m .Only 800 bridges are made of prestressed concrete superstructures and all others are with reinforced concrete, steel and arches. The most popular types of prestressed beams used in Sri Lanka are inverted T, M, I, and the box beams. The inverted T and M beams are widely used. Further, for 30m span simply supported bridges, space rectangular box beams and spaced trapezoidal box beams were used. For the continuous bridges big spine beams also have been used with post tension pre-stressing system in recent bridge constructions. For longer span bridges, box beams are highly suitable. Generally box beam has higher torsional capacity because of its closed geometry. The enhanced torsional stiffness of the box beam sections improves the load distribution properties for the superstructure. It has higher bending carrying capacity and requires reduced beam height compared to other beam section for a particular span. Hollow spaces in box beams can be used for services and it is also aesthetic. In Sri Lanka 19% of the existing bridges are with prestressed concrete and presently many highway projects are under construction. Therefore, the usage of box beams will improve the effect on the time of construction, cost, construction easiness, aesthetic considerations and utility services. There are different types of box beams available that can be used for this simply supported span range. They are standard box beam, standard U beam and spaced box beams. The rectangular spaced box beam has been used for a two lane bridge in a 30m simply supported span and the trapezoidal spaced box beam has been used for a four lane elevated flyover in Sri Lanka. Comparative analysis and design on all these box beams are useful for future bridge constructions. This research is concentrated on the design of 30m simply supported four lane bridge super structures using the above different types of prestressed box beams separately. The results of analysis and design and the properties of the beams are compared. The total width of the designed bridges is 17.4m. It has a central reserve of 1.2m. There are four lanes; each lane is 3.5m width. There are two pedestrian walk ways of 1.1m width. All the bridge decks were modeled in SAP 2000 for the grillage analysis. Loading was done according to BS 5400: Part 2, 1978, and bending moments, shear forces and torsional moments were found for critical load combination. Prestressing designs were carried out for all beams and the final results are compared. Cost for each deck also compared. The different launching methods adapted for these Bridges are also compared. Conclusions and recommendations are laid down based on these compared results.
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    item: Thesis-Abstract
    Structural design of prestressed concrete continuous double tee beam bridges
    Ranasinghe, WMDN; Jayasinghe, MTR
    One of the applications of prestressed concrete is in continuous bridges. These can be either double tee or box girders. The longitudinal shape can be prismatic, semi-prismatic or non- prismatic. The design of these bridges otTer a considerable challenge to the design engineer due to the presence of secondary moments which are induced due to the prestressing forces. These introduce a considerable complexity to the design process. In this research, an attempt is made to develop a design method that would minimize the complexity associated with the design of prismatic prestressed concrete double tee bridges. In concrete bridges, generally the minimization of self weight is important. This is used as the criterion to start the design process. The governing criteria for the various components of the cross section is used to determine the smallest section that is practically possible. The methods to take account of short term and long term effects such as creep and shrinkage are also included for the cross section selected. Once the cross section is available, it is necessary to find appropriate cable forces. Design methods for both constant and variable cable forces are presented based on the line of thrust. It is shown that the use of variable cable forces could reduce the total cable forces thus leading to a saving in tendons. For the selected cable forces, it is necessary to ensure that cable profile will be available within the selected section. The line of thrust can be transformed to fit within the section by selecting a suitable set of secondary moments. Thus, the secondary moment can be selected in a straightforward manner for both constant and variable cable forces. Thus the cable profile selected should ensure that it fits within the limits of cable profile zone and also generate the selected secondary moments. This is not a trivial task. In order to simplify this task, a design method was introduced for both constant and variable cable forces. In the case of variable cable forces, there is a possibility to have point moments and forces acting at the cable force change points. A method to deal with such forces is also introduced. Therefore, it is possible to consider that this thesis presents a complete design method for the preliminary design of prismatic double tee prestressed concrete beam bridges either with constant or variable cable forces. It has also shown that it is possible to minimize the complexity of difficult design tasks by approaching the problem in modular fashion. Keywords - Prestressed Concrete, Double Tee bridges