Currently, the design for structural vibration induced by human walking is based on the walking forces obtained on rigid surfaces. It is largely unknown how footstep forces would be modified if the surfaces are vibrating, especially when the step frequency is near the natural frequency of pedestrian structures (e.g., footbridges). The proposed tests aim to reveal the interaction mechanism between pedestrians and vibrating structures by combining testing and analysis techniques from human motion science and structural engineering. The tests consist of two test series: Phase I and Phase II. In particular, Phase I will be mainly conducted on VSimulators (VSim) motion platform facility and Phase II will be carried out on Exeter bridge (a FRP footbridge located at Exeter Science Park). The present test plan is developed for Phase I at VSim.

A group of 12 healthy participants (6 male and 6 female) will be recruited in this study from students and staff in the University of Exeter. During pre-test visit, their physical data (e.g., body mass, height, leg length) will be measured as well as walking speeds. During Phase I tests, participants will be asked to walk on a treadmill placed on the VSim platform at their selected walking speeds (see Figure below). The platform will oscillate with different combination of frequency, amplitude and duration. Metabolic cost, kinematic data and ground reaction force (GRF) will be recorded.

Phase II tests will be conducted on the Exeter Footbridge outside of the VSim building (see Figure below). A pair of insole pressure sensors will be put in the shoes to measure the GRF.

The study was approved by College of Engineering Mathematics and Physical Sciences Ethics Committee.

Metabolic tests

Location

VSimulators is in the University of Exeter Engineering Research Centre, a newly built facility at Exeter Science Park, which completed construction in February 2020. VSimulators is housed in half the building, which includes the VSimulators chamber, a control room, a workshop, a meeting room/break out room, office space, and toilet facilities/showers on each floor (with full disabled access).

Main capabilities

A 3.7m x 3.7m octopod motion platform (designed and built by E2M) within an 8m x 8m room. The platform moves on six degrees of freedom: Z axis (vertical motion); X axis (anterior-posterior); Y axis (medio-lateral), and then a series of movements which involve rotation about Z-axis (yaw), Y-axis (pitch)) and X-axis (roll). It is designed for high fidelity reproduction of small motion signals with limits set at maximum displacement +/- 21 mm and maximum acceleration 2 m/s², the upper limit equating approximately to significant discomfort experienced by humans. This enables simulation of a wide range of scenarios in the frequency range from 0 to 40 Hz. This platform can replicate actual data recorded from real environment situations (examples include vibration in floors, ship sway and train motion). The motion platform is secured onto an isolation block to prevent interference with environmental vibration.