Robustness and overstrength of structures under impacts

Protection and safety of humans are basic needs and have become important issues in the past decades. The ability to address these needs is a multidisciplinary task for which the expertise of various disciplines is required. Engineers, specifically civil engineers, are responsible for the built environment. Civil engineering structures are designed to support both ordinary and extreme loads acting on them during their lifetime. Structural design for extreme events, natural and man-made hazards (accidental or malevolent) has two components: first, the occurrence and intensity of the hazard events, and secondly, the consequences of such events. The effects of extreme loading conditions such as impact on engineering structures have been widely investigated in an attempt to develop safe and efficient design approaches. Research efforts on the protection of civil structures has become important with the increase of terrorist attacks around the world. Besides hostile attacks, man-made accidents and natural events such as rockfalls, landslides, tsunamis, etc., generate impact loads on structures. Although such kind of events is relatively rare, their effects on structures and the associated consequences may be catastrophic. The present study focuses on the effects of extreme events on structures, in particular the behaviour of structures under impact loads (Chapters 1 and 2). When designing a structure to withstand impact, it is important to consider not just the response of an individual member, but to consider the whole-structure response to the damage caused. In addition, extreme events can be singular events, where the absence of event, likelihood and demand data make it difficult to design structures for specific abnormal loads. In presence of events that are not foreseeable, the focus has to be shifted to approaches that address robustness and general structural integrity to control the consequences of an unexpected event. The traditional approaches to implement robustness in structures tend to limit the propagation of damage through a design based on the consequences (Chapter 3). A literature review, the knowledge gaps and the key strategies in collapse analyses are reported. In this light, a general method for a consistent and quantitative measure of structural robustness of frame structures is proposed (Chapter 4). The effects of damage scenarios on frame structures, which represent a common structural scheme example of highly connected structure, are investigated. As a result, a methodology capable of increasing the structural robustness is explored. The philosophy of this approach is different from classical strategies since structural members are designed for variable reliability levels, depending on the member’s influence to produce system consequences. In this methodology, the role of overstrength in a robustness-oriented design is considered (Chapter 5).