Semi‐Active Movable Shear Keys for Seismic Response Control of Bridges

The size of the joint gaps plays a significant role in the dynamic performance of bridges. This has recently motivated the consideration of movable shear keys (MSKs), pioneered by the corresponding author, to enhance bridge performance by changing the bridge support/boundary conditions. Previously, adaptive‐passive MSKs have been developed to adjust the joint gap in a one‐off operation based on the intensity of the incoming earthquake estimated from early warning systems. Herein, a novel semi‐active control system is proposed and numerically assessed, which exploits the potential of MSKs to adjust the bridge boundary conditions in real‐time (i.e., during the earthquake). The proposed system aims to achieve effective seismic vibration control by locking (on the abutment seat) or unlocking (and hence permitting sliding) the MSKs, based on displacement‐based limit state (LS) thresholds checked in real‐time. This is achieved by an innovative modification of the MSKs to facilitate the controlled movement, as well as by a binary (on‐off) closed‐loop control algorithm, which makes the on‐off decision by comparing the real‐time response measurements of all bridge critical components against predefined thresholds. The thresholds are specified by performance requirements corresponding to different LSs of each critical bridge component in a performance‐based design setting. The proposed control system is evaluated using nonlinear response history analyses (NLRHA) of an MSK‐equipped typical bridge under sets of response spectrum compatible non‐pulse‐like, and near‐fault pulse‐like ground motions. Through a comprehensive parametric study, suitable thresholds in the form of safety factors per component are identified for quasi‐optimal performance of the case‐study bridge for two different LSs, while the MSK properties that considerably affect the semi‐active control approach are identified. Significant reductions in seismic bridge demands are observed compared to a bridge passively controlled with MSKs, leading to a considerable increase in the global safety factor and the earthquake intensity at which the selected LSs are exceeded, thus showcasing the proposed semi‐active control strategy as a promising solution for enhancing the seismic performance of bridges.