Lifetime extension of a realistic model of an in-service bridge through a response modification approach

Many highway bridges in the United States are reaching their intended design lives and are in need of attention. To avoid replacing these bridges simultaneously, methodologies to safely extend their lives are important to help avoid high replacement costs and to allow for bridge replacement to occur over a longer time window. This paper expands an approach to extend the fatigue life of vulnerable steel bridges through a response modification (RM) apparatus, consisting of a mechanical amplifier and a RMdevice, which provide efficient supplemental stiffness and damping to the bridge. Because of the relatively small deflections encountered under typical service loads, the use of a mechanical amplifier allows for a more efficient and less intrusive apparatus to provide the required RM forces imparted to the bridge for increased bridge life. This paper presents a parameter study exploring the flexibility of the elements in the RM apparatus, the length of the apparatus, and the characteristics of the RM device. The analyses also add superstructure damping and other model improvements to a comprehensive numerical model of a realistic in-service bridge. The paper carries out dynamic analyses in the frequency domain to ensure the robustness of the RM apparatuses for various loading frequencies. The most important characteristic of the RM apparatus is found to be the cross-sectional area of the members. Additionally, the parameter study showed that a smaller apparatus is most cost effective. Finally, the dynamic analyses showed that the use of a semiactive device may be beneficial to the effectiveness of theRMapproach.