A framework for experimental determination of localised vertical pedestrian forces on full-scale structures using wireless attitude and heading reference systems

Abstract

A major weakness among loading models for pedestrians walking on flexible structures proposed in recent years is the various uncorroborated assumptions made in their development. This applies to spatio-temporal characteristics of pedestrian loading and the nature of multi-object interactions. To alleviate this problem, a framework for the determination of localised pedestrian forces on full-scale structures is presented using a wireless attitude and heading reference systems (AHRS). An AHRS comprises a triad of tri-axial accelerometers, gyroscopes and magnetometers managed by a dedicated data processing unit, allowing motion in three-dimensional space to be reconstructed. A pedestrian loading model based on a single point inertial measurement from an AHRS is derived and shown to perform well against benchmark data collected on an instrumented treadmill. Unlike other models, the current model does not take any predefined form nor does it require any extrapolations as to the timing and amplitude of pedestrian loading. In order to assess correctly the influence of the moving pedestrian on behaviour of a structure, an algorithm for tracking the point of application of pedestrian force is developed based on data from a single AHRS attached to a foot. A set of controlled walking tests with a single pedestrian is conducted on a real footbridge for validation purposes. A remarkably good match between the measured and simulated bridge response is found, indeed confirming applicability of the proposed framework

A Robust Methodology for the Reconstruction of the Vertical Pedestrian-Induced Load from the Registered Body Motion

“…In addition, in [14], it is shown that, for the involved six sensor positions, including L5 and T6 (sixth thoracic vertebrae), the strongest correlation exists between the GRFs and the accelerations of the BCoM. It is noted, however, that, in [16], an even better correlation with the GRFs is found when using the C7 accelerations, in particular for slow walking speeds. The sampling frequency of the inertial units was set to 60 Hz, as recommended by the manufacturer for a configuration of six sensors.…”

“…As direct force measurements are in this case practically infeasible, indirect force measurements, where the input is reconstructed from registered body motion, constitute an interesting alternative. Promising results have been obtained for the reconstruction of the ground reaction forces (GRFs) induced by walking, bobbing and jumping, generally using visual marker data [8,[11][12][13] and in some cases using inertial sensors [14][15][16][17][18][19]. In [12], Racić et al apply Newton's second law of motion and the vertical accelerations at the centre of mass (CoM) of 15 body segments, in order to reconstruct human bouncing and jumping forces.…”

“…Although marker-based technologies are the golden standard for laboratory applications, they are practically infeasible for application in the field involving a large number of participants because of marker occlusion and the limitations of the tracking devices in terms of distance. An interesting alternative is the use of individually-adopted sensor technologies, such as inertial sensors [14][15][16][17][18][19]. In [15], a laboratory setup involved a single pedestrian whereby the vertical acceleration levels close to the BCoM are measured simultaneously with the induced GRFs.…”

“…In their work, a linear model is proposed that can be trained for an individual, to estimate the GRFs with a high level of accuracy from the acceleration levels registered at C7, L5 and one of the thighs. Bocian et al [16] showed that using the nominal body mass with the motion of C7 in Newton's second law yields an absolute error in the amplitude of the component of force at the pacing frequency of less than 15 percent at a 90 percent confidence level. Furthermore, Bocian et al [16] use the data collected by wireless altitude and heading reference systems to estimate the spatial location of application of the pedestrian forces.…”

“…Bocian et al [16] showed that using the nominal body mass with the motion of C7 in Newton's second law yields an absolute error in the amplitude of the component of force at the pacing frequency of less than 15 percent at a 90 percent confidence level. Furthermore, Bocian et al [16] use the data collected by wireless altitude and heading reference systems to estimate the spatial location of application of the pedestrian forces. In [17], Brownjohn et al use the data collected by wireless inertial units at C7 and Newton's second law to arrive at a good estimate of the GRFs induced by jumping.…”