Experimental Evaluation of the Influence of Human-Structure Interaction for Vibration Serviceability

Lightweight pre-cast flooring systems using post-tensioning to increase strength but not stiffness are increasingly popular, and vibration serviceability problems tend to govern design of such floors where human occupants are increasingly concerned with vibrations. At the same time as inducing response, stationary human observers can also participate in the response as mitigating influence and it is clear that a human behaves as a highly effective damper, even when seated.Experiments were done to study energy flow and storage in a 1.2 tonne vibrating concrete plank with a human occupant. Results showed that damping could increase to as much as 10% frequency shifts (usually decreases) in the slab apparent resonant frequency, depending on occupant posture. Simple lumped mass mathematical models were also used to study the vibrating human-structure system through dynamic simulations, corroborating the findings.Further corroboration was provided from measurements on a prototype full-scale floor slab occupied by several hundred people who were either jumping or sitting. Modal analysis of vibration response signals showed that normal floor resonance associated with jumping at a sub-harmonic of the floor natural frequency was almost completely damped out by the passive (seated) people.

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Vertical Vibrations of Footbridges Due to Group Loading: Effect of Pedestrian–Structure Interaction

Applied Sciences ◽

10.3390/app11041355 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1355

Author(s):

Paweł Hawryszków ◽

Roberto Pimentel ◽

Rafaela Silva ◽

Felipe Silva

Keyword(s):

Dynamic Systems ◽

Resonance Condition ◽

Realistic Model ◽

Vertical Vibration ◽

Structure Interaction ◽

Codes Of Practice ◽

Vibration Serviceability ◽

Vertical Vibrations ◽

Pedestrian Crossing ◽

Vibration Signatures

The vibration serviceability of footbridges has evolved from the adoption of a single pedestrian crossing in the resonance condition to load cases in which several pedestrians cross the structure simultaneously. However, in spite of this improvement, pedestrians continue to be considered as applied loads in codes of practice. Recent research has pointed out that modeling pedestrians as dynamic systems is a step further in the search for a more realistic design approach. This is explored in this paper, focusing on the case of vertical vibration. A two-span cable-stayed test structure was selected, and accelerations were measured from single and group crossings, both at the structure and at a pedestrian’s waist. Numerical simulations considering the pedestrians modeled as loads only and also as dynamic systems were implemented, and numerical and experimental time response vibration signatures were compared. Reductions of up to 25% and 20% in peak and RMS acceleration, respectively, were obtained when pedestrians were modeled as dynamic systems, in comparison with the less realistic model of pedestrians as loads only. Such reductions were shown to depend on the number of pedestrians involved in the group. The results, thus, highlight that pedestrian–structure interaction is an asset for the vibration serviceability design of footbridges.

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