Risk assessment of strait crossing bridges
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The purpose of this thesis is to try to provide an overall risk picture for the planned strait cross- ing (SC) bridges on coastal highway E39 between Trondheim and Kristiansand in Norway. The thesis starts off by explaining the concepts and solutions of SC bridges to understand what the National Public Road Administration (NPRA) is planning to accomplish with the coastal high- way E39. The SC bridges cannot be compared to any other bridge structures in the world, which will lead to some challenges. The biggest challenge with these crossings is the depths of the fjords. General risk assessment theory is briefly explained. In addition the general practice for the NPRA and other relevant applications are presented to get an understanding of what have been done when it comes to risk assessment of bridges and tunnels. The necessity of a new approach to risk assessment for SC concepts is discussed. Hazard identification methods are described and discussed. Some of the methods described are used to identify the hazards and hazardous events for the three different SC concepts. It has been distinguished between hazards related to location/environment and hazards related to construction. Some knowledge about risk metrics and risk acceptance criteria is presented. It is discussed how to establish risk acceptance criteria for the SC concepts. This discussion is based on theory and the use of acceptance criteria from other applications. One preliminary conclusion of the discussion says that the NPRA should learn from other applications, but be careful not to copy directly from others. It is suggested that the NPRA modify their plan processes to make a better environment for risk assessment. A new and general approach to risk assessment for SC concepts is suggested. This approach is more detailed and structured than the existing procedure at the NPRA, and should be applicable to all the different concepts. To exemplify the approach a case study of a submerged floating tunnel crossing Halsafjorden is performed. The conclusion of this thesis is that a change in routines regarding risk management is nec- essary for the NPRA to ensure the safety of SC concepts. An improved risk assessment approach with substantial risk acceptance criteria needs to be established. The solutions suggested in this thesis are a step in the right direction, but there are still numerous challenges, especially regard- ing the risk acceptance criteria, that need to be solved before a full risk picture of the SC bridges is achieved.