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This project is a 32.5 ECTS-point master thesis developed at the Technical University of Denmark (DTU). The master thesis concerns the design of a two-span composite highway bridge spanning across a motorway. The bridge is designed to have a carriageway width of 17 meters and a total length of 69.5 meters. The two spans of the bridge are unequal with the lengths of 29.5 and 40 meters, respectively. The bridge is carried out with stainless steel girders and pre-fabricated concrete decks. The aim is to develop a new type of bridge structure with reduced maintenance cost, which can be erected with as minimal disruption of the track as possible. The design of the composite bridge in this thesis is based on the dimensions of a post-tensioned concrete bridge, which is under construction at Egebækvej in the city of Nærum, Denmark. Because stainless steel is a rather new structural material for bridge structures, a literature study has been carried out in order to clarify the dierent grades of stainless steel and their characteristics. This literature study has also led to some examples of existing bridges, in which stainless steel has been used for the load-carrying system. The nal design of the composite bridge consists of eight double symmetric I-girders with a constant height of 1080mm, carrying pre-fabricated concrete decks on top with a constant thickness of 250mm. The stainless steel girders are made of the Duplex stainless steel grade 1.4462. This grade is chosen on the basis of its mechanical properties and durability to corrosion. The pre-fabricated reinforced concrete decks are fabricated with a concrete of class C50/60, having a characteristic strength of 50MPa. The bridge design has been modelled in the commercial FE-program for bridge engineering MIDAS Civil. The design has been veried on the basis of linear static analyses, as well as moving load analyses performed with this bridge tool. The results of the analysis and verication is a bridge structure with adequate load-carrying capacity in relation to the load combinations carried out in this thesis. Two stages have been used during the analysis of the structure; a construction stage only taking the self-weight of the stainless steel girders and concrete decks into account, and an operating stage taking the moving load and self-weight of the surfacing into account. The bare girders have been designed on the basis of the construction stage and the composite section has been designed using the section forces for the operating stage, both with use of the theory of elasticity. In order to support the girders and connect the bridge structure to the foundation, xed pot bearings have been chosen at the intermediate support and uni-dimensional pot bearings have been selected at the end supports. Dimensions and resistances of the bearings have been ascertained in order to absorb the reactions and displacements from the various types of loads. At last, an estimate of the total construction cost of the bridge has been carried out in order to make a cost comparison with the reference concrete bridge."
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