Dynamic Behaviour of Concrete Structures subjected to Blast and Fragment Impacts
Sammanfattning: For protective structures, reinforced concrete is commonly used. Concrete structures subjected to explosive loading in a combination of blast and fragments will have very different response than statically loaded structure. During the blast and the fragment impacts the structure will shake and vibrate, severe crushing of concrete occurs and a crater forms (spalling) in the front of the concrete; for large penetration, scabbing may occur at the backside of the wall, or even perforation, with a risk of injury for people inside the structure. This thesis is intended to increase the knowledge of reinforced concrete structures subjected to explosive loading, i.e. effects of blast and fragmentation. A further aim is to describe and use the non-linear finite element (FE) method for concrete penetration analyses. Particular attention is given to dynamic loading, where the concrete behaviour differs compared to static loading. The compressive and tensile strengths increase due to the strain rate effects. Initial stiffness increases, and moreover the concrete strain capacity is increased in dynamic loading. Traditionally, for prediction of the depth of penetration and crater formation from fragments and projectiles, empirical relationships are used, which are discussed here together with the effects of the blast wave that is caused by the explosion. To learn more about the structural behaviour of concrete subjected to severe loading, a powerful tool is to combine advanced non-linear FE analyses and experiments. A trustworthy model must be able to capture correct results from several experiments, including both the depth of penetration and the crater size. In this thesis, FE analyses of concrete penetration with steel projectiles have been performed and compared to existing experimental results. By using the non-linear FE program AUTODYN, the depth of penetration and crater sizing can be predicted.
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