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

From phase drift to synchronisation – pedestrian stepping behaviour on laterally oscillating structures and consequences for dynamic stability

AcceptedJournal ArticleThis is the final version of the article. Available from Elsevier via the DOI in this record.© 2016 The AuthorsThe subject of this paper pertains to the contentious issue of synchronisation of walking pedestrians to lateral structural motion, which is the mechanism most commonly purported to cause lateral dynamic instability. Tests have been conducted on a custom-built experimental setup consisting of an instrumented treadmill laterally driven by a hydraulic shaking table. The experimental setup can accommodate adaptive pedestrian behaviour via a bespoke speed feedback control mechanism that allows automatic adjustment of the treadmill belt speed to that of the walker. 15 people participated in a total of 137 walking tests during which the treadmill underwent lateral sinusoidal motion. The amplitude of this motion was set from 5 to 15 mm and the frequency was set from 0.54 to 1.1 Hz. A variety of stepping behaviours are identified in the kinematic data obtained using a motion capture system. The most common behaviour is for the timing of footsteps to be essentially unaffected by the structural motion, but a few instances of synchronisation are found. A plausible mechanism comprising an intermediate state between unsynchronised and synchronised pedestrian and structural motion is observed. This mechanism, characterised by a weak form of modulation of the timing of footsteps, could possibly explain the under-estimation of negative damping coefficients in models and laboratory trials compared with previously reported site measurements. The results from tests conducted on the setup for which synchronisation is identified are evaluated in the context of structural stability and related to the predictions of the inverted pendulum model, providing insight into fundamental relations governing pedestrian behaviour on laterally oscillating structures.Mateusz Bocian was supported by the UK Engineering and Physical Sciences Research Council via the University of Bristol Doctoral Training Account (EP/P50483X) for a part of the work presented in this study. The Wellcome Trust (089367/Z/09/Z) is acknowledged for funding for the experimental setup, through an infrastructure development grant to the Bristol Vision Institute. Professor Alan R. Champneys of the Department of Engineering Mathematics at the University of Bristol is acknowledged for providing comments leading to the improvement of the manuscript

Beam losses from ultra-peripheral nuclear collisions between Pb ions in the Large Hadron Collider and their alleviation

Electromagnetic interactions between colliding heavy ions at the Large Hadron Collider (LHC) at CERN will give rise to localized beam losses that may quench superconducting magnets, apart from contributing significantly to the luminosity decay. To quantify their impact on the operation of the collider, we have used a three-step simulation approach, which consists of optical tracking, a Monte-Carlo shower simulation and a thermal network model of the heat flow inside a magnet. We present simulation results for the case of Pb ion operation in the LHC, with focus on the ALICE interaction region, and show that the expected heat load during nominal Pb operation is 40% above the quench level. This limits the maximum achievable luminosity. Furthermore, we discuss methods of monitoring the losses and possible ways to alleviate their effect.Comment: 17 pages, 20 figure

Nutritional and physicochemical meat properties of wild boar (Sus scrofa ferus) x Duroc pig slaughtered to different live weights

AbstractDuring the past few years, an increasing interest has been shown for wild and autochthonous pig, that can offer meat of high culinary, technological and health-promoting value. Production of hybrids (wild boar x swine) can be a valid way to give back some properties to pig meat, lost in commercial swine breeding. This study, conducted in a farm in Wronie (Poland), was designed to investigate the effects of slaughter weight and gender on nutritional and physicochemical meat properties derived from crossing the European wild boar (Sus scrofa ferus) with sows of Duroc breed. Twenty-six hybrids (16 barrows and 10 gilts) were reared in pens, housed according to sex, and were fed ad libitum, from a hog feeder, with a feed containing 12,5 MJ of EM/kg and 160g of CP/kg. Animals were slaughtered at two different live weights: 8 barrows and 5 gilts at 92,0 ± 4,2 kg and 8 barrows and 5 gilts at 108,1 ± 4,3 kg. Animals were electrically stunned; following exsanguination, the carcasses were dehaired and evisce..

Salmonella contamination of pig farm environment, Poland, 2014

Although pork is considered an important source of Salmonella infections, the introduction of control programs in pig farms are not obligatory in the EU. To resolve current epidemiological situation, monitoring of pig farms was introduced in Poland in 2014. The paper reports the first year outputs of the survey

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

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.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.The research presented here was funded by EPSRC (grant EP/I029567/2). Authors thank Devon County Council for permitting the experimental campaign to be conducted on Baker Bridge in Exeter, UK, and Dr Erfan Shahabpour (supported by EPSRC grant EP/K03877X/1) for providing access to and assisting with measurements on the ADAL-3D treadmill at the University of Sheffield (funded by EPSRC grant EP/E018734/1)