Footbridge dynamic performance assessment using inertial measurement units

This is the author accepted manuscriptDynamic performance of footbridges is still a great concern to designers, operators and users, with many structures requiring investigation before, during and after construction to manage performance. We have been investigating the use of wireless inertial measurement units (IMUs) designed for biomechanics, health and sports science application for estimating human dynamic loads or ground reaction forces (GRFs) on structures. The aim has been to move from direct measurements using force plates and treadmills, via optical motion capture in the laboratory (with application of Newton’s Second law), to unconstrained field conditions. Initially we used IMUs to evaluate pedestrian synchronisation, but we found that a single IMU attached to the C7 neck vertebra can provide a remarkably accurate estimate of vertical GRF. With an ability to communicate and synchronise within a group wirelessly, to identify orientation and transform accelerations into world coordinates, IMUs can identify both the GRF force vectors and their time varying location with a moving pedestrian. As a side-benefit, the signal to noise ratio and synchronisation accuracy are sufficient to enable low-cost wireless footbridge ambient vibration testing and monitoring. So far we have used IMUs for ambient and forced vibration testing (the latter using a human shaker), moving pedestrian load and response measurement and crowd tracking. There are many more possibilities

Measured dynamic properties for FRP footbridges and their critical comparison against structures made of conventional construction materials

This is the final version. Available from Elsevier via the DOI in this record.This paper reports new experimental data for dynamic properties (i.e. modal mass, natural frequency and damping ratio)of eight FRP composite footbridges in Europe, which helps to resolve the weakness in knowledge and understanding of dynamic properties of FRP footbridges. In addition, dynamic properties are reviewed with the results of six other FRP footbridges and 124 non-FRP footbridges built after 1991. A comprehensive comparison of these 138 sets of dynamic properties shows that FRP footbridges possess similar fundamental frequencies at the same span, but usually higher damping ratios (mean of 2.5% c.f. mean of <1.0% for steel, concrete and steel-concrete composite). Additionally, natural frequencies and damping ratios identified from free decays measured on FRP footbridges are response amplitude dependent. Comparing the accelerance peaks of FRP and conventional footbridges revealed that the FRP footbridges are, on average, around 3.5 times more responsive to resonant excitation than the conventional bridges having the same bridge length, deck width and mode shape due to their significantly lower modal mass.UK Engineering and Physical Sciences Research (EPSRC) Counci

Análisis por condición de servicio causado por vibración vertical inducida por peatones en estructuras

Civil engineering structures such as grandstands, slabs, footbridges and staircases have reported unacceptable vertical vibration when they are affected by human activities. Even when most of these structures are designed according to current guidelines and design codes, there are still misunderstandings in the human-structure interaction effects that, in some cases, may increase the vibration response compromising the structural serviceability performance. As a result, the serviceability load conditions due to pedestrian activities control, in most cases, the design for these structures. Therefore, a systematic overview regarding vertical pedestrian-structure interaction is carried out to demonstrate the need for a realistic analysis to properly incorporate these effects toward more rational structural designs. The discussion establishes a body of knowledge regarding pedestrian loads and structural responses, yielding the potential for more rational approaches to improving the analysis and design of pedestrian structures.Estructuras civiles tales como tribunas, losas, puentes peatonales y escaleras están presentando vibraciones verticales inaceptables cuando se ven afectadas por actividades humanas. Por lo tanto, todavía no se tiene claridad sobre los efectos producidos por la interacción entre el ser humano y la estructura que, en algunos casos, pueden llegar a aumentar la respuesta estructural comprometiendo el desempeño para condiciones de servicio. Un examen a las normas y códigos de diseño existentes, arroja una amplia gama de resultados, lo que demuestra que no son consistentes cuando las estructuras están expuestas a cargas inducidas por peatones. Este estudio tiene como objetivo identificar los mecanismos de vibración, los modelos matemáticos y los métodos para abordar la vibración vertical excesiva en las estructuras peatonales. Este análisis establece un conjunto de recomendaciones sobre las cargas que producen los peatones y las respuestas estructurales que pueden producir, lo que genera el potencial para futuros enfoques más racionales que mejoren el análisis y el diseño de estructuras peatonales

Influence of low-frequency vertical vibration on walking locomotion

Walking locomotion has been a subject of studies in diverse research fields, such as computer, medical, and sport sciences, biomechanics, and robotics, resulting in improved understanding of underlying body motion and gait efficiency and pathology (when present). Only recently, a detailed understanding of kinematics and kinetics of the walking locomotion has become an important requirement in structural engineering applications due to an increasing sensitivity of modern, lightweight, low-frequency, and lightly damped footbridges to pedestrian-induced dynamic excitation. To facilitate development, calibration and verification of pedestrian models requires experimental characterization of walking gait parameters and understanding whether and how these parameters are influenced by the structural vibration. This study investigates whether low-frequency vibrations in the vertical direction affect seven walking locomotion parameters: pacing frequency, step length, step width, angle of attack, end-of-step angle, trunk angle, and amplitude of the first forcing harmonic. Three participants took part in a testing program consisting of walking on a treadmill placed on both stationary and vibrating supporting surfaces. The collected data suggest that an increasing level of vibration results in an increase in step-by-step variability for the majority of parameters. Furthermore, the existence of the self-excited force, previously observed only in numerical simulations of walking on pre-excited bridge decks, was confirmed. In addition, the deck vibration tended to have a beneficial effect of reducing the net force induced into the structure when walking at a pacing rate close to the vibration frequency. Finally, it was found that the vibration level perceptible by a pedestrian is one to two orders of magnitude larger than that typical of a standing person, and that the sensitivity to vibration decreases as the speed of walking increases

Mitigation of human‐induced vertical vibrations of footbridges through crowd flow control

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Influence of Low-Frequency Vertical Vibration on Walking Locomotion

This is the final version. Available on open access license from American Society of Civil Engineers via the DOI in this recordData Availability: Electronic format of the data collected in this research can be downloaded freely from the University of Warwick webpages http://wrap.warwick.ac.uk/79038/.Walking locomotion has been a subject of studies in diverse research fields, such as computer, medical, and sport sciences, biomechanics, and robotics, resulting in improved understanding of underlying body motion and gait efficiency and pathology (when present). Only recently, a detailed understanding of kinematics and kinetics of the walking locomotion has become an important requirement in structural engineering applications due to an increasing sensitivity of modern, lightweight, low-frequency, and lightly damped footbridges to pedestrian-induced dynamic excitation. To facilitate development, calibration and verification of pedestrian models requires experimental characterization of walking gait parameters and understanding whether and how these parameters are influenced by the structural vibration. This study investigates whether low-frequency vibrations in the vertical direction affect seven walking locomotion parameters: pacing frequency, step length, step width, angle of attack, end-of-step angle, trunk angle, and amplitude of the first forcing harmonic. Three participants took part in a testing program consisting of walking on a treadmill placed on both stationary and vibrating supporting surfaces. The collected data suggest that an increasing level of vibration results in an increase in step-by-step variability for the majority of parameters. Furthermore, the existence of the self-excited force, previously observed only in numerical simulations of walking on pre-excited bridge decks, was confirmed. In addition, the deck vibration tended to have a beneficial effect of reducing the net force induced into the structure when walking at a pacing rate close to the vibration frequency. Finally, it was found that the vibration level perceptible by a pedestrian is one to two orders of magnitude larger than that typical of a standing person, and that the sensitivity to vibration decreases as the speed of walking increases.Engineering and Physical Sciences Research Council (EPSRC

From individual behaviour to an evaluation of the collective evolution of crowds along footbridges

This paper proposes a crowd dynamic macroscopic model grounded on microscopic phenomenological observations which are upscaled by means of a formal mathematical procedure. The actual applicability of the model to real world problems is tested by considering the pedestrian traffic along footbridges, of interest for Structural and Transportation Engineering. The genuinely macroscopic quantitative description of the crowd flow directly matches the engineering need of bulk results. However, three issues beyond the sole modelling are of primary importance: the pedestrian inflow conditions, the numerical approximation of the equations for non trivial footbridge geometries, and the calibration of the free parameters of the model on the basis of in situ measurements currently available. These issues are discussed and a solution strategy is proposed.Comment: 23 pages, 10 figures in J. Engrg. Math., 201

Operational modal analysis and continuous dynamic monitoring of footbridges

Tese de doutoramento. Engenharia Civil. Universidade do Porto. Faculdade de Engenharia. 201