Enhancing the robustness of steel and composite buildings

Methods intended for use in the design of steel and composite building frames covering the provision of adequate robustness so as to guard against progressive collapse are in the process of moving from prescriptive to quantitative. An approach that recognises all the important complex physical phenomena, employs a realistic criterion of failure and is capable of being implemented at a variety of levels has been devised at Imperial College London. Recent further development of this method has streamlined the necessary analyses, thereby making it possible to conduct parametric studies that provide insights into the link between changes to the structure and quantitative measures of resistance to progressive collapse. This approach is used herein to examine a number of different arrangements, from which key features of behaviour are identified. It has therefore been possible to isolate those structural modifications with the greatest potential for improving robustness and, moreover, to associate quantitative measures of that improvement with each scheme. Results for a series of arrangements, including several proposals put forward by Industry as methods of improving robustness based on the simple notion of increased tying capacity, are examined herein and general principles for improvement identified.