Abstract
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.
Highlights
The use of fibre reinforced polymers (FRPs) in aerospace, automotive and shipbuilding industry is well-established, so applications in spaceships, planes, cars and boats are widely known and common
An ultra-lightweight FRP footbridge, whose linear mass is only 80 kg/m, has been been considered as benchmark structure to identify a Human-Structure Interaction (HSI) model, in which a walker is described via a MSDA system
As the supported structure exhibited significant vertical vibrations due to a single pedestrian, who walked over the bridge synchronising the fourth harmonic of the action with the bridge’s fundamental frequency, the proposed HSI model considers load factors of the first four harmonics of the human activity
Summary
The use of fibre reinforced polymers (FRPs) in aerospace, automotive and shipbuilding industry is well-established, so applications in spaceships, planes, cars and boats are widely known and common. By preventing natural frequencies of a structure within this range, excessive vertical human-induced vibrations are assumed to be avoided and dynamic response analysis is not mandatory This may not be applied to FRP footbridges as researchers have demonstrated that the dynamic behaviour of composite footbridges may be affected by higher and less energetic harmonics of pedestrian actions [5,14]. Since the first proposal from Archbold [25], several models [26,27] accounting for the dynamic parameters of the human body have been used to consider HSI on the dynamic response of footbridges Under this approach, the mass, frequency, and damping ratio of the human body together with an external force are employed along with the properties of the structure, leading to a coupled human-structure vibrating system.
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