Structural Response With Regard to Explosions

Abstract: When a structure is subjected to an explosion, it will have a response that differs from the one that arises from a static load. Engineers are used to design for static loads but the common knowledge of how to design for explosions is weak. There are guidelines for how to design for explosions with simplified methods but they are partly outdated and the explanation of how they are derived is vague. This Master thesis compiles some of the most important guidelines and explains the underlying theory. In order to understand the structural response one must first study basic theory of explosions, different material behaviours and basic dynamics, which are also presented in the thesis. A structure can be simplified by transformation into a single degree of freedomsystem(SDOF-system), and the reliability of such an SDOF-system is evaluated within this thesis. The SDOF-system is created by using a system point where the maximum displacement will occur, and it is compared to hand calculations for the maximum values and to non-linear finite element analyses. The SDOF-model assumes a specific deflection shape which is taken into account by using certain transformation factors. The simplified methods of calculating the structural response are presented in general, but the examples are made for reinforced concrete beams as these, due to their high mass and ductile behaviour, often are used as protection from explosions. Since no actual tests could be performed to collect empirical data about the response, FE-analyses are performed with the finite element software ADINA and even for a complex material such as concrete these analyses are assumed to represent the actual response of a structure. In order to speed up the analyses, adequate simplifications of the motion can be described with mode superposition, and the effectiveness of these simplifications is shown in the thesis. When the mode superposition-analysis is made with only one mode, the results can verify the accuracy of the SDOF-model. When designing structures it is important that the calculations are on the safe side to minimize the risk of damage and above all, failure, and therefore damping is often neglected as it is both easier to calculate without it and the results will be on the safe side. However, in order to get more accurate results the damping should also be included and therefore different approaches for this are described. For impulse loads the moments near the supports are initially larger than for a static load which could pose a problem when the reinforcement is shortened in these areas. In this Master thesis the response for curtailed concrete beams is studied.