Optimal design and application of a MTMD system for a glulam footbridge under human-induced excitation

Modern glued-laminated timber (glulam) footbridges are usually designed as slender structures and easily influenced by human-induced vibrations, because of their low stiffness, damping and modal mass. If the main vibration applicability requirements cannot be met, some measures such as tuned mass dampers (TMDs) should be taken to reduce the vibration. This paper discusses the vibration serviceability assessment of a glulam model bridge subjected to realistic pedestrian traffic conditions, and the optimal design of multiple tuned mass dampers (MTMDs). The model is an approximately 13 m long three-hinged deck arch bridge, including two circular arch ribs with the radius of 8.7 m. The fundamental frequency in the vertical of the footbridge was within the critical range given by the recent European guidelines EN 1990 and BS 5400. This required further analysis to assess the vibration serviceability of the bridge relative to the maximum acceleration thresholds. Besides the peak dynamic response obtained from the pedestrian interaction tests, peak acceleration was calculated according to the Chinese guideline JTG D60 and compared with the comfort limits. The results of experiment and analysis show that the peak vertical and lateral accelerations of the model bridge should be checked under single- or crowd-induced loading for the serviceability limit state (SLS). It simplifies the solution procedure and makes the result slightly safer by replacing the pedestrian moving load with fixed-position stepping to excite the footbridge. A genetic algorithm based optimization method can be used to solve the multi objective optimization problem of the MTMD design for the reduction of human-induced vibrations.