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Improved computer calculation model for slide ways
2002 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The goal of this senior design project is to find an improved calculation model for slide ways. Slide ways serve as support in bridge construction, when a new bridge replaces an old one. They are only temporary constructions and are removed after the new bridge is in place. The focus in this report is on how the load is transferred onto the slide way. Does the load act as a uniform load or will it act as a few concentrated loads, since steel has a higher flexibility than concrete? If the case is a few concentrated loads, then this is positive when it comes to dimensioning. The bending moment will then be smaller than that of a distributed load. The slide ways in the study are all steel constructions. The reason for finding an improved calculation model was to see if it could lead to smaller dimensions of the slide way. Smaller dimensions would mean a lower material cost, and thus a possibility to save money. The study has been done in two parts. The first part considers influence lines for a simply supported beam with a distributed load and two concentrated loads respectively. Parameters used were both the length of the beam and the load intensity. By varying these two parameters and displaying the outcome in diagrams, the differences between the two cases become clear. Further calculations of shear force and bending moment are done with a German structural program called mb. This program has several options one of which is a frame structure. A number of vertical elements are introduced to study the distribution of the load. The vertical elements, bars, carry together the weight of the bridge construction. By only accepting pressed or unloaded bars the picture of the load distribution becomes clear. The load can be moved along the beam and for different positions on the beam the load acts differently, either as a distributed load or concentrated loads. The second part of the study is the program SLIDE, a calculation program written in MATLAB. The program is similar to the frame structure in mb, but not as extensive. It only calculates shear force, bending moment, deflection, contact pressure and reaction forces and does not dimension like mb. It is also more automatic in comparison to mb. The results of the influence line evaluation show that the length of the beam is the most significant parameter, which affects the size of the bending moment. The calculations with mb show that the model using concentrated loads is more realistic than a distributed load for a concrete structure. But mb’s drawback is that the calculations are time-consuming. When the load is moved, new coordinates need to be given by hand, and this also applies when vertical elements under tension are removed. SLIDE on the other hand does not dimension, but it calculates shear force, bending moment and deflection, which can be compared to results in mb. SLIDE’s foremost advantage is that it is quick in comparison to mb. New coordinates do not need to be given when the load is moved along the beam. This is run by a step function. Likewise, vertical elements are removed automatically. The program calculates until it finds a stable state, where all the vertical elements are pressed or unloaded. The state of the vertical elements, pressure or unloaded, is displayed through colours, blue for pressure and red for unloaded. Two main conclusions can be drawn from this study. When a concrete bridge on a steel slide way can be seen as two concentrated loads, the dimensioning bending moment will then be substantially smaller than that of a distributed load. Smaller beam dimensions can be used and hence the cost decreases. Secondly, the program SLIDE, specifically written for the project, is faster than mb and has a clear graphic display.

Place, publisher, year, edition, pages
Keyword [en]
Technology, brolansering, lanseringsbana, ramanalys
Keyword [sv]
URN: urn:nbn:se:ltu:diva-57353ISRN: LTU-EX--02/156--SELocal ID: e0949f8a-c280-477e-a8d1-9c83ffb963f9OAI: diva2:1030740
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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