Robustness of passive and semi-active control schemes on a cable stayed bridge under extreme loading conditions

The modern design of large complex structures must comply with an increasing level of performance expectation, both from the point of view of safety requirements, which must be satisfied under an increasing number of loading conditions, as well as from the point of view of serviceability. Structural control solutions can give an important contribution to achieve the high standards of performance, feasibility and safety required. Related is the issue of robustness. In buildings this is defined as their insensitivity, in terms of performance, to damage occurrence and it has been recognized as a desirable characteristics of structural systems because it allows the system to perform efficiently under different conditions, and mitigates its susceptibility to progressive collapse. A similar definition can be applied to control systems. The main goal of the present study consists in the evaluation of the control system performance, for an iconic cable-stayed bridge, when local failure occurs in the control system devices. A model of the cable-stayed bridge is developed at the numerical level in a commercial finite element code, starting from original data. The model is used to simulate the structural response under extreme loading conditions, such as seismic excitation. Different types of control systems for the mitigation of the bridge response, implementing passive and semi-active dampers respectively, are employed following some previous results from the literature. An additional goal of this work to be underlined is the investigation of a way to quantify the change in performance of the control system, under equivalent loading condition. To this end, some general observations, by means of a proposal for quantitative robustness indexes in terms of control performance, are provided. Some comments on the relations between these outcomes and the type of cable supported bridge selected are provided as well by comparison with the results coming from a companion paper that deals with these same issues with reference to a suspension bridge.