THESIS
2012
xx, 173 p. : ill. (some col.) ; 30 cm
Abstract
Accidental explosions and terrorist activities have in recent years raised the awareness of the research community on the structural robustness and stability of civilian constructions. In the engineering community, however, there are limited resources available for blast analysis and design of structures. Existing design tools are almost exclusively based on the traditional single-degree-of-freedom approach, whose accuracy and applicability are both questioned for certain structures. Reinforced concrete slabs are good examples of these structures, but unfortunately, they are also one of the most extensively used and important component in civil structures and buildings. Their blast performance is crucial to the overall stability and integrity of the whole structural system. It is not on...[
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Accidental explosions and terrorist activities have in recent years raised the awareness of the research community on the structural robustness and stability of civilian constructions. In the engineering community, however, there are limited resources available for blast analysis and design of structures. Existing design tools are almost exclusively based on the traditional single-degree-of-freedom approach, whose accuracy and applicability are both questioned for certain structures. Reinforced concrete slabs are good examples of these structures, but unfortunately, they are also one of the most extensively used and important component in civil structures and buildings. Their blast performance is crucial to the overall stability and integrity of the whole structural system. It is not only a problem that the predictions of the existing design codes are sometimes over-conservative, but that the inconsistency in accuracy and reliability implies a handicap of such methods in properly modelling dynamically loaded slabs. There is thus an urgent need to develop a practical yet theoretically sound method of analysis for blast-loaded reinforced concrete slabs.
In this thesis, analytical modelling techniques are developed to improve the representation and hopefully the understanding of the dynamic deformation process of reinforced concrete slabs under intense dynamic loading. With sufficient accuracy, they may serve as useful alternatives to computer simulations for blast response estimates. In view of the limited distribution of computing software and expertise devoted to high-end numerical modelling in the engineering practice, the present developments have their values in providing practical tools for large-scale preliminary blast analysis and design on the one hand, and substituting the conventional methods to present to the practitioners a more realistic and comprehensive analytical modelling procedure of the dynamic response on the other.
The membrane actions in reinforced concrete slabs play a significant role in their complicated behaviour during blast response, involving the evolution and transition of failure mechanisms. A theoretical procedure is proposed in the framework of concrete plasticity to derive the internal resistances as functions of the deflection level, the mechanism geometry, the slab properties, and, of course, the boundary conditions. With consistency preserved with the internal kinematical compatibility, the progressive developments of membrane actions are clarified for both homogeneous and reinforced concrete slabs, and for both the cases of clamp supports with external in-plane restraints and simple supports without them. The proposed procedure and its results bridge a link between yield line theory and dynamic plasticity, so that the flexural-membrane behaviour of reinforced concrete slabs can be properly modelled in the dynamic analysis. A rigid-plastic slab model is then developed by an implementation of the foregoing results in the dynamic rigid-plastic analysis of rectangular slabs. The newly developed formulations govern and guide the dynamic slab response through different stages of membrane actions. To suit practical situations in real constructions, a further development is carried out to accommodate the effects of asymmetrical support conditions. Blast assessment shows that the present model can serve as an efficient yet accurate and consistent analytical tool for the prediction of the dynamic response of blast-loaded reinforced concrete slabs.
In a significant portion of practical constructions, reinforced concrete slabs are supported by secondary beams or girders which have limited load carrying capacities and are susceptible to plastic hinge formation in case of intense loading like blast that can well exceed their design load levels. Various failure mechanisms, ranging from slab-type, beam-type, to composite-type, are discovered for beam-supported slabs in high dynamic loading scenarios, and a consistent framework of rigid-plastic models is developed to describe their dynamic collapses conforming to every one of them. The collection of models work together by facilitating the evolutions and possible transitions of the collapse pattern from one failure type to another during dynamic response. Except for performing computer modelling, conventional design tools hardly capture such complicated behaviour of beam-supported slabs. The present approach based on dynamic plasticity thus enables the practical blast assessment to extend beyond the level of single components to the combined failure of multiple components. This will be valuable to the engineering practice in view of its efficiency and minimal resources required.
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