| Summary: | The infrastructure of today is getting older and problems caused by deterioration over time is affecting the service life of these structures. In Sweden most of the existing bridges were constructed 60 to 70 years ago, rising the need to determine the state of health of the bridges as the maintenance costs will increase heavily. Part of the above-mentioned cut of the bridges owned by Trafikverket (The Swedish Transport Administration) that was constructed 60 – 70 years ago are pre-stressed concrete bridges. Pre-stressing of concrete structures is today a commonly used technology that utilizes the beneficial characteristic of concrete, the compressive strength, to a further extent than reinforced concrete. This report will focus on the problems with pre-stressed concrete bridges and particularly on the thermal effects on the Abiskojokk railway bridge located in the northern part of Sweden. The pre-stressed box girder bridge spans in total 86 m in three lengths of 30 m, 35 m respectively 21 m starting from the east abutment and is part of the Iron-Ore Line starting in Kiruna and ending in Narvik, Norway. In an ocular(särskild) inspection of the bridge carried out the 18th of August in 2016 several crack patterns were mapped on the inside of the box girder along with some cracks about the top of the first column support starting from the east abutment. This thesis is focusing on the cracks that was mapped along the tendon positions on the inside of the box girder in the first span starting from the east abutment. The hypothesis is that the cracks are caused by temperature loads and normal forces obtained from the tendons at the thickening of the cross-sections. The research questions are; what the monitoring program shows and if it is possible to prove the hypothesis by using of a FE-model considering the gravity loads, temperature loads and the pre-stressing. In order to determine the cause of the cracks on the inside of the box girder and investigate the behaviour of the bridge a monitoring program was installed, ...
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