Study of demolition processes for prestressed concrete bridges: Kalix bridge

Abstract: Bridges in Sweden are getting older and some of them are reaching their designed life span. With an older generation of bridges, the need for a good understanding of demolition processes increase. The Kalix bridge is planned to be demolished and will be used as a case study in this thesis. A bridge demolition must be customized for the bridge and all special regulations regarding the bridge and the surrounding area. To find the most suitable demolition process for a specific bridge a great amount of knowledge of both the bridge, the area and possible demolition techniques are needed. This thesis investigates some common bridge demolition methods and how they affect the surrounding area. It is also of great importance to make a structural analysis of the bridge to ensure a safe demolition. A finite element analysis is therefore conducted of the bridge and the demolition steps. The Kalix bridge is a prestressed concrete box girder bridge with a total length of 283.6 meters divided into five spans. The bridge is situated in a Natura 2000-area, which is an important area for biodiversity. Natura 2000 is a European Union project that works to preserve the biodiversity. Specific rules and restrictions are assigned for each Natura 2000-area to protect the sensitive species in the area. The sensitive area must be considered when choosing the demolition process, since the area should not be disturbed. It is of importance to have good knowledge about the possible demolition techniques to make an informed decision. In this thesis several common demolition methods are presented. Because of the sensitive area not all demolition techniques are suitable, which is evaluated for the demolition methods. The demolition methods that are presented in the thesis are: • Machine mounted demolition attachments• Blasting• Wrecking ball• Sawing and cutting• Splitting• Jackhammers• Hydro demolition• Thermal demolition A structural analysis of every step of the demolition process is conducted. The structural analysis is done for every demolition step due to the change of capacity and loads when parts of the structure is removed. The safest way to demolish a prestressed bridge is to demolish it the opposite way of the construction process, which is considered for the analysis. The result from the analysis of the demolition of Kalix bridge show good results, with few signs of damages. There is a risk of cracks due to tension stress in the concrete for some of the demolition steps.