Robustness and Vulnerability of Flat Slab Structures

A structure is robust if is insensitive to external disturbances and can withstand localized damage without disproportional consequences. Conversely, a structure is vulnerable if can be easily affected by any damage which produces consequences disproportional to that damage. Standard strategies and rules concerning the safety of concrete structures in case of catastrophic events or actions are based on two alternative assumptions. According to the first, desired structural integrity can be achieved by providing redundant load-transfer path within the structure. According to the second assumption, the structure should be designed with regards to prevent the progressive collapse, unwanted mechanisms of destruction and to limit the extent of damage and deformity of elements, connections, and the whole structure. In this paper, the importance of assessing both the structural robustness and vulnerability of flat slab structures to catastrophic and unforeseen events is highlighted and analyzed. As risk assessment is essential where uncertainty of input parameters have a significant impact on behavior, damage and collapse of a structure, its vulnerability and robustness are evaluated in terms of the risk that can be tolerated. Because of the vague nature of possible hazards and their consequences, semi-quantitative approach to risk estimation by means of fuzzy numbers has been used. An analysis of an example flat slab structure shows that such an approach makes possible to assess weak and strong points of a structure due to its form, external actions and extreme events.