Investigation of Retrofit Strategies to Extend the Service Life of Bridge Structures through Active Control

The durability of aging bridge structures has become a serious societal concern. It has been estimated that 40%-50% of the bridge stock in Europe and 36% in the US is approaching and exceeding the intended service life in some cases. Conventional retrofitting methods are generally effective under predetermined loading scenarios and can mitigate to some extent the effect of damage through strengthening and stiffening. However, typical retrofit measures involve the addition of components, which might cause unwanted stress accumulation, and in addition, they cannot perform adaptation after damage to recover functionality. Adaptive structural systems can modify the response under loading using sensors and mechanical actuators, instead of relying solely on the resistance offered through material and geometry. Previous work has shown that well-designed adaptive structures are effective in reducing peak responses under strong loading resulting in configurations that embody far fewer material and carbon resources than conventional passive systems. This work investigats retrofit strategies using active control through mechanical actuators integrated into the bridge's primary load path or as external systems. The objective is to extend the durability of most common bridge types including beam, tied-arch, and cable-stayed. Two active retrofit systems are considered: (1) an external adaptive tensioning (EAT) for beam bridges; (2) linear actuators placed in the hangers and stays of tied-arch and cable-stayed bridges. Depending on the failure mode (e.g., corrosion-, fatigue-induced), the effect of active control is simulated through a quasi-static controller based on least-squares minimization or through a linear quadratic regulator and explicit time-history analysis. Results shows that the stress reduction achieved by the EAT system retrofitted to a concrete bridge with corrosion-induced damage could extend service by approximately 12 years. In both cable-stayed and tied-arch bridges, the stress range amplitude caused by vehicular traffic is reduced below the constant amplitude fatigue limit, potentially extending service beyond 75 years.