Response modification approach for safe extension of bridge life

A large portion of highway bridges in the United States are reaching or have reached their intended design lives. To avoid replacing a large number of bridges simultaneously, methodologies to safely extend their lives are important to help avoid high replacement costs and to schedule bridge replacement over a longer time window. This paper proposes an approach to extend the fatigue life of vulnerable steel bridges through a response modification apparatus, consisting of a mechanical amplifier and a response modification device, which provides 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 smaller apparatus and enables a more efficient device to provide adequate response modification forces to the bridge. Herein, the use of a scissor jack as the mechanical amplifier is proposed for use in bridge applications, and its utility in concert with a passive stiffness device is demonstrated by application to a simple beam structure. Reductions in moment ranges of 37% and safe life extensions of 300% are achieved on a simple beam model with the proposed response modification apparatus.