Due to the high strength-to-weight ratio of fibre reinforced polymers (FRPs), human-induced vibration problematic remains as a subject to be fully comprehended in order to extend the use of composites in Bridge Engineering. Thus, this paper studies an ultra-lightweight FRP footbridge, which presents excessive vertical vibrations when the fourth harmonic of a walking pedestrian is synchronised with the structure’s fundamental frequency. Focusing on the vertical bending mode, at 7.66 Hz, the bridge dynamic behaviour was assessed under the action of a single pedestrian crossing the facility at a step frequency of 1.9 Hz. As an over prediction of the footbridge response was computed using a moving force (MF) model available in a design guideline, a mass-spring-damper-actuator (MSDA) system was adopted to depict a walker. Hence, Human-Structure Interaction (HSI) phenomenon was considered. Employing the experimental results, parameters of the MSDA system were identified, leading to a HSI model that considers the first fourth harmonics of a walking human. Additionally, a parametric analysis was carried out, determining that the damping ratio of the human body and the load factor associated to the fourth harmonic are the most relevant parameters on the estimation of the response. The identified HSI model may be used as a first approximation to accurately predict the dynamic response of ultra-lightweight composite structures and should be extended to account for crowd-induced loads.

Fiber-reinforced polymers (FRPs) have enabled the construction of lightweight footbridges, whose structural design is often governed by a serviceability limit state. A suitable approach to avoid overdimensioning an FRP footbridge may be to adopt a motion-based design strategy, where excessive human-induced vibrations are mitigated through the installation of tuned vibration absorbers (TVAs). In this sense, human–structure interaction (HSI) phenomena should be considered to estimate accurately the acceleration response of lightweight footbridges and size TVAs properly. Thus, this paper presents the design, installation, and performance assessment of a passive inertial controller for completing the construction of a full-scale FRP pedestrian structure. First, a general frequency-domain procedure to design TVAs for structures susceptible to HSI is proposed. The methodology considers a multiobjective optimization problem that minimizes simultaneously the structural response and the controller inertial mass. Second, the HSI load model of a bouncing pedestrian is identified experimentally to be used within the proposal to design TVAs. Third, a TVA of 25 kg is designed, assembled, and installed in the lightweight FRP structure, employing the proposed procedure. Then, the enhancement of the dynamic response due to the controller is assessed considering a person bouncing and two streams of walking pedestrians. For the different load scenarios, the TVA exhibits an adequate behavior to mitigate the vertical acceleration, demonstrating the feasibility to deliver an ultralightweight FRP footbridge with an inertial controller to meet requirements at different limit states.

Due to current architectural trends, contemporary public buildings are becoming open-plan spaces with much less weight and damping. Consequently, Vibration Serviceability Limit State (VSLS) due to human-induced vibrations has become an increasing concern for structural engineers, especially when designing offices, hospitals, or gymnasiums. When dealing with resonant vibrations, a slight increase in the floor-damping enables decreasing considerably the vibration level. The damping strategy studied in this work is usually known in the literature as Constrained Layer Damping (CLD) and consists of a viscoelastic layer constrained between the concrete slab and the steel beam of a lightweight composite floor. In this paper, a complete structural checking methodology has been developed for analyzing all the limit states that determine the final sizing of a steel–concrete composite floor treated with CLD, including a detailed analysis of the VSLS. The methodology has been used for setting a structural optimization problem for floors with and without CLD treatments. Thus, it has been demonstrated that the integration of CLD treatments at the design stage of the building allows the development of lighter floor structures with a smaller embodied carbon (EC) footprint, especially for long-span schemes with restrictive vibration limitations.