Dynamic loading factors of individual jogging forces

Abstract

With increasingly popular marathon events in urban environments, such as in London and New York City, structural designers are faced with a great deal of uncertainty when assessing dynamic performance of bridges occupied and dynamically excited by people running. While the dynamic loads induced by people walking have been intensively studied since the infamous lateral sway of the London Millennium Bridge in 2000, reliable and practical descriptions of running excitation are still very rare and limited. This paper makes a step forward by bringing together a unique database of individual jogging force records and their simple mathematical model which can be used in everyday design practice. The forcing data has been collected in Vibration Engineering Section Laboratory in the University of Sheffield using a state-of-the-art instrumented treadmill, which is commonly used in clinical studies of human gait and sports biomechanics. The modelling strategy featuring Fourier harmonics of measured jogging force-time histories is adopted from a popular design guidelines for human walking excitation of structures. The results show a great scatter in the DLF data and no strong link with jogging footfall rate, which is the case with walking forces. This clearly suggests that traditional deterministic Fourier based approach is not the best modelling strategy for jogging loading. Uncertainty and inter-personal randomness of the force amplitudes indicate that stochastic - rather than deterministic models of jogging forces should provide more reliable predictions of the bridge dynamics. These forces could be modeled in a similar fashion as other key dynamic loading of structures characterized by great randomness and uncertainty, such as wind and earthquake.