Theoretical Analysis And Experimental Study On The Robustness Of Cable Supported Structures

Due to the interference caused by abnormal events and the uncertainties of structures or loads, the structures may suffer from localized damages, which may lead to the overall collapse or disproportional collapse. Since the balcony collapse of the Ronan Point apartment in London caused by the gas explosion in the18th floor in1968and the tragic9-11event, the concept "prevention of disproportional collapse caused by initial damage", i.e. structural robustness, has attracted increased attention from scholars around the world. At present, the qualitative and quantitative research on the structural robustness is not uncommon, yet there exists neither a uniform theory of structural robustness, nor exists agreement about the used design method. Besides, while most research have focused on trusses, frames, bridges as well as grid structures, little attention has been paid to the robustness of cable supported structures. According to the property of interference, this article will investigate the structural robustness from the aspects of initial damage and uncertainty, the framework of robust design of cable supported structures based on continuum topology optimization will also be proposed.First of all, while the characteristics of deterministic performance-based robust indices are of objectivity, expressiveness, simplicity and calculability, the degradation of material is simulated with the damage index of the cross-section of members; the structural performance measures are derived and concluded and based on that, a set of indexes of structural robustness are defined; the robust indexes are then used in the evaluation of a truss and a rigid cable dome and their applicability is analyzed. It is shown that the energy and the Euclidean scalar norm of displacement based robust indexes are the most appropriate measure for structural robustness.Secondly, from the point of uncertainty, the structural and load uncertainties are modeled with info-gap theory, this is then combined with the performance requirements and the robust index is established with the consideration of disturbance of normal loads and structural attributes. Considering the nest optimization problem of the robust function, the Particle Swam Optimization Method is used to solve this problem and the performance diagrams are drawn with regard to the uncertain interval models and the robustness of a truss and a rigid cable dome is analyzed. It can be concluded that the info-gap decision theory based robust index is both simple and expressive to reveal the relationship between the initial uncertainties and the disproportional results.Finally, based on H∞control theory, the structural robustness is accessed with the H∞norm of the structure system transfer function. Following the SIMP approach, an artificial isotropic material model with penalization for elastic constants is assumed and relative density variables of elements are used for describing the structural layout. The robust topology optimization problem is then modeled as to search for the minimum robust index and the particle swarm optimization algorithm is used to solve the problem. Taking cable supported doubly curved spherical shell as an example; the topology configuration was obtained with the robustness based design method. Finally, two cable supported reticulated shells were designed with the robustness based and the conventional design method respectively. The interference scenarios were imitated with the experiments of static overloading and impact loading and the robustness of the two models were analyzed and compared. It is shown that the H∞based robustness measure can reflect whether the consequences is disproportionate or not and structural behavior is marginally affected by the changes of environmental conditions, which further provide new potentials to the conceptual design process of cable supported structures.