A Research On Quantification Of Structural Robustness

Robustness is an important concept in the field of engineering structure to resist progressive collapse. Design codes of many countries require that structures be designed to be capable of resisting abnormal events that might lead to progressive collapse, however, these requirements are of the qualitative level. Though there have been many structural robustness indexes, no quantitative measure of structural robustness is generally accepted, which derives from the different usage of robustness by different scholars.Concepts relevant to structural robustness are differentiated and analysed in the present thesis, and a semi-deterministic framework for robustness assessement is built. Structural uncertainty, i.e., variation of materials and geometry dimensions, under a specific event is ignored, and uncertainty of different events is considered via an occurrence probability density function. Robustness in this study is investigated according to its opposite property, i.e., structural vulnerability. View the structure as an assembly of discrete components, then the structural vulnerability could be obtained via set theory correspondingly. According to the different contribution to structural vulnerability, a bearing capacity-based component importance coefficient(CIC) is introduced as the weight coefficient of component vulnerability coefficient(CVC), and a robustness index is further obtained.For both truss and reinforced concrete(RC) frame structures, suitable CICs and CVCs are provided. As for truss structures, CICs can be calculated through the incremental load method, where failure scenarios trigged by failure of different components and internal topology between components are revealed. The existence of axial force only makes the CVCs be difined at the strain level. As f or RC frame structures, CICs are calculated via the pushover analysis. Only change in ultimate structural bearing capacity is of concern and the complicate failure scenarios are neglected. Due to the complexity in internal forces distribution of RC compone nts, CVC is defined at the internal forces level to consider failure criteria under the interaction of tension, compression, bending moment and shear force.Numerical examples of four trusses and five RC frames are performed to demonstrate the use of the proposed robustness index. Distribution of CICs and CVCs among each structure are compared and analysed, and robustness assessment of each structure is made. Analysis results show that the robustness index provided good explanation to assessment of structural robustness under different events. Increasing the local resistance and redundancy of the structure are two effective methods to upgrade structural robustness.