Vulnerability and robustness analysis of structures

• Main Author: Zhuang, Wenjuan
• Published: University of Bristol 2015
• Subjects: 624.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682728

A structure is robust if it can res'ist any action without disproportionate consequences. If it is vulnerable to any action under any circumstance it cannot be robust. Progressive failure of Ronan Point building in London in 1968, Alfred Murrah building in Oklahama in 1995 and World Trade Centre in 200 I have highlighted the need for reducing vulnerability. There are many measures of structural vulnerability and robustness, each with its own strengths and weaknesses. Some only depend upon the structural form and the others more concentrate upon the loading. The objectives of this research are to investigate the vulnerability and robustness of structures through an analysis of the form of the structure and the distribution of strain energy and to propose measures to improve it. A theory of structural vulnerability, previously developed at Bristol, focuses on the form of structure to identify vulnerable failure scenarios. A measure of structural well-formedness which uses member stiffness matrices and connectivity is central to it. An improved measure of structural well-formedness is developed. This better accounts for the supports and leads to better results for many cases such as the loss of a ground storey column which is common in progressive collapse studies. This is a hazard independent analysis and helps to identify low probability, high consequence scenarios. The consequences of an initial damage to a structure can be strongly sensitive to the applied loads. A structure will remain stable if the structural elements are able to redistribute released energy and dissipate any excess energy. The distribution of energy depends on both the form of the structure and the loading. Hence, a new approach to vulnerability based on strain energy distribution is developed. Numerical experiments are carried out to examine energy transition characteristics and the ability of the structural members to absorb energy. These show that the sequence of damage progression can be obtained from energy distribution. Higher gains in strain energy densities of members after the loss of a member indicate higher damage potential. A robust structure would have a smaller value of structural strain energy density and an even distribution of energy amongst members. It is also found that strengthening certain combination of members can significantly lower the changes in strain energy after damage and thus prevent collapse propagation. Several other indices to evaluate structural vulnerability are studied and a comparison is made with the newly developed energy approach. Numerical examples show that the new energy approach works well. It captures the practical structural responses better than stiffness-based indices. The vulnerability of a structure can be reduced by controlling the flow of energy and dissipating energy as damage propagates. For this purpose, the use of shape memory alloys (SMA) is investigated experimentally and numerically. Small models of concrete beams and columns incorporated withmartensite and austenite SMA cables are tested. The austenite SMA concrete members show high recovery and resistance capacities. The martensite SMA concrete members are found to be good at dissipating energy. The tests suggest that is possible to improve the robustness of structures by reinforcing with both martensite and austenite SMAs and larger scale tests may be carried out in future work.