Blast analysis of normal concrete, high strength concrete and ultra-high performance concrete members

Abstract

The understanding of different failure modes of reinforced concrete members is essential in the blast analysis and design of civil and defence structures. Normal concrete (NC) is a widely used material in structures; high strength concrete members (HSC) is undergoing widespread use in civil engineering and construction processes and ultra-high performance concrete (UHPC) is deemed to be a promising material due to its high ductility, impact resistance and energy absorption capacity and it has drawn intense interests for the purpose of blast resistant design of structures. This thesis contains five journal papers, which aim to extend, or produce new analytical techniques for investigating both shear and flexural failure modes of structural members made of these three kinds of materials by considering both experimental and theoretical studies. The thesis has been divided into three chapters. Chapter 1 is the introduction and problem statement of this research work. Chapter 2 contains two journal papers and it provides the absence of method for assessing direct shear failure mode of reinforced concrete (RC) members against blasts. Chapter 3 includes three journal papers, which present experimental and theoretical study of failure modes of high strength reinforced concrete (HSRC) members and ultra-high performance fibre reinforced concrete (UHPFRC) members under explosion loads. Finally, Chapter 4 presents conclusions of this research program. The experimental investigations on behaviour of reinforced concrete structures subjected to blast loading have revealed that direct shear mechanisms play an important role in the overall response and failure mode of structures. However, most of previous studies are based on the assumption that only flexural response dominates failure mode without taking shear failure into consideration. Therefore, the first journal paper in Chapter 2 is to use single degree of freedom (SDOF) system as a tool for predicting direct shear response of blast loaded reinforced concrete members. In addition, as there are no design provisions that are available to predict shear stress to slip relationship for design of NRC members, the second journal paper assesses direct shear response of NRC members is numerically evaluated using finite element software LS-DYNA, which has not been investigated in the previous literature. The two papers in Chapter 2 provide new insights concerning the mechanics of dynamic shear failure of NRC members against blast loading. Chapter 3 presents a blast testing program on ultra-high performance fibre reinforced concrete (UHPFRC) and high strength reinforced concrete (HSRC) columns and a one dimensional (1D) finite element model (FEM) is then adopted for further investigations, due to its inherent accuracy and stability despite its numerical efficiency. The third journal paper represented herein is devoted to investigating experimentally the mechanical properties and dynamic responses of ultra-high performance twisted steel fibre reinforced concrete and HSRC columns under both quasi-static and blast loads. Afterwards, the fourth journal paper gives a detailed investigation of the capabilities of ultra-high performance micro steel fibre reinforced concrete columns and high strength reinforced (HSRC) columns against close-in blasts. To achieve this objective, a series of blast tests were conducted to investigate the behaviour of UHPFRC columns HSRC columns subjected to blast loading. Lastly, the fifth journal paper uses 1D FEM to accurately analyse the response of UHPFRC and HSRC columns subjected to blasts. This thesis deals with a broad range of topics in analysing the static and dynamic response of structural members including RC members, HSRC and UHPFRC columns. The static loading regimes include the direct shear response. The dynamic loading regimes include impulse loading due to real blast experiments. The failure modes under blast loading conditions have been addressed in great details both in experimental study and numerical simulations.