Efficient dynamic performance assessment of footbridge

issue: 4articleCopyright © ICE Publishing, all rights reserved.The dynamic performance of footbridges has become a significant concern in recent years, resulting in increasing demand for assessment of the performance of new and existing footbridges subject to pedestrian loading scenarios far more complex than the existing code provisions. Performance assessment typically involves predictions based on numerical simulations using finite-element representations and pedestrian load models, possibly followed by experimental assessment under normal and limiting load conditions. As dynamic performance is strongly related to all the modal parameters of the bridge, namely modal frequency, damping, shape and mass, their reliable identification for modes to be involved in pedestrian-induced response is central to assessment. The paper describes an efficient procedure for assessing dynamic characteristics and performance using a combination of visual survey, finite-element modelling and brief and unobtrusive dynamic testing, followed by short observation of pedestrian-induced response and finite-element model updating for evaluating other loading scenarios. The procedure involves minimal effort for maximum effect, generating a reliable analytical representation for response simulation and checking the serviceability of the bridge. The procedure has been tested using an existing non-problematic bridge, as described here, before being used on new structures

The dynamic stiffening effects of non-structural partitions in building floors

PublishedIt is commonly known that full-height non-structural partitions of a fitted out floor structure affect its dynamic properties, with increase in floor mass and modal damping being commonly quoted in floor design guidelines. As a consequence, it is generally accepted that the non-structural elements usually reduce the response of floors to walking excitation. There is very little understanding of the effects of full-height partitions on the stiffness of building floors and this effect is generally not taken into account in floor design guidelines. This paper is therefore focused on establishing experimentally the effects of full-height non-structural partitions on dynamic stiffness of a full-scale real-life composite building floor. Modal testing data are presented for three construction phases of the floor: from a completely bare floor via partially to fully-fitted floor. The effects of the partitions are shown by comparing the measured frequency response functions (FRFs) at the same location for different construction phases and the estimated key modal properties of the floor corresponding to these phases. This kind of multi-phase measurements on a real-life floor structure during construction is very rare due to its logistical complexity and long-time required to gather data through all of the phases. It is shown that the partitions significantly affect measured FRFs by increasing damping, and in particular, floor stiffness. It is also shown that the mode shapes are changed by the partitions. The magnitude of the changes is quantified experimentally which is one of the first attempts to do this on a real-life floor structure using high-quality FRF measurements. © The Society for Experimental Mechanics, Inc. 2013

Modal testing of Tamar suspension bridge

startedmonth: FebruaryCopyright © 2002-2016. Society for Experimental Mechanics, Inc.As part of a continuing investigation on the Tamar Suspension Bridge, vibration measurements on the Tamar Bridge were conducted on two occasions. Using three sensors, the first measurement (in 2005) identified possible deck vibration modes and characterised the performance of new additional stay cables. The second measurement, in 2006, used 16 accelerometers to characterise the motion of main and side spans as well as the towers, by means of identification of a full set of modal parameters (except modal masses). The procedures for these two brief operational modal tests are described with the significance of some of the findings in relation to the 'structural mechanisms' of the bridge

Floor vibration serviceability in a multistory factory building

ArticleExperimental and analytical modal analysis and in-operation vibration measurements were performed on the massive concrete structural floors of several structurally connected ‘units’ of a six-level, multitenant industrial complex with total floor usable area exceeding 0.1 km2. The aim of the systematic study was to characterize vibration sources and factors that affect vibration serviceability, which is a major concern when changing usage patterns lead to conflicting requirements for vibration generation and tolerance for different types of industrial/ commercial user. This was a rare investigation aiming to provide information on specific performance and relevant technologies for occupancy decisions by tenants and building management of similar structures. Floors evaluated were within different types of industrial singleoccupant unit stacked up to six levels and having multibay floors with spans up to 12 m with first vibration mode frequencies greater than 8 Hz. These “high-frequency floors” display typical transient response behavior to footfalls, with response levels controlled by modal mass. Units were studied in typical operational conditions including warehousing, instrument assembly and testing, light electronic/mechanical manufacturing, and machining. Vibration sources included internal and external vehicles, human footfalls, and machinery. The study showed the most onerous form of loading to be forklift trucks and that higher level floors of the same type were least serviceable. Experimental modal analysis showed a surprising range of modal properties for nominally identical floors of the same type and the relevance to performance of modal mass

Temperature and ac Effects on Charge Transport in Metallic Arrays of Dots

We investigate the effects of finite temperature, dc pulse, and ac drives on the charge transport in metallic arrays using numerical simulations. For finite temperatures there is a finite conduction threshold which decreases linearly with temperature. Additionally we find a quadratic scaling of the current-voltage curves which is independent of temperature for finite thresholds. These results are in excellent agreement with recent experiments on 2D metallic dot arrays. We have also investigated the effects of an ac drive as well as a suddenly applied dc drive. With an ac drive the conduction threshold decreases for fixed frequency and increasing amplitude and saturates for fixed amplitude and increasing frequency. For sudden applied dc drives below threshold we observe a long time power law conduction decay.Comment: 6 pages, 7 postscript figure

Vibration serviceability assessment of floors in a multi-use, multi-storey industrial complex

Structures Congress 2014, Boston, Massachusetts, United States, 3 - 5 April 2014Vibration serviceability assessments were carried out on the floors of several 'units' of an industrial complex in Singapore. Floors tested were within large, two-level, structural units described as detached, semi-detached and terraced and having usable single floor areas up to 2100 m2. All floors were constructed from hollow core slabs with spans up to 12 m and all nominally behaved as high frequency floors. Occupancy conditions ranged from empty and untenanted to usage for warehousing, instrument assembly and testing, electronic equipment manufacture to light manufacturing and machining of metal structures. Forms of loading included internal and external vehicles, human footfalls and excitation by machinery. The study identified the most onerous form of loading and provides guidance for facility owners with mixed vibration serviceability requirements

Stability of Spatio-Temporal Structures in a Lattice Model of Pulse-Coupled Oscillators

We analyze the collective behavior of a lattice model of pulse-coupled oscillators. By studying the intrinsic dynamics of each member of the population and their mutual interactions we observe the emergence of either spatio-temporal structures or synchronized regimes. We perform a linear stability analysis of these structures.Comment: 15 pages, 2 PostScript available upon request at [email protected], Accepted in Physica

Suppression of airway inflammation by Illicium verum and trans-anethole

_Background_ SH2 domain containing inositol-5-phosphatase (SHIP1) is an important modulator of innate and adaptive immunity. In mice, loss of SHIP1 provokes severe ileitis resembling Crohn's disease (CD), as a result of deregulated immune responses, altered cytokine production and intestinal fibrosis. Recently, SHIP1 activity was shown to be correlated to the presence of a CD-associated single nucleotide polymorphism in ATG16L1. Here, we studied SHIP1 activity and expression in an adult cohort of CD patients. _Methods_ SHIP1 activity, protein and mRNA expression in peripheral blood mononuclear cells from CD patients in clinical remission were determined by Malachite green assay, Western blotting an

Dynamic Ordering and Transverse Depinning of a Driven Elastic String in a Disordered Media

We examine the dynamics of an elastic string interacting with quenched disorder driven perpendicular and parallel to the string. We show that the string is the most disordered at the depinning transition but with increasing drive partial ordering is regained. For low drives the noise power is high and we observe a 1/f^2 noise signature crossing over to a white noise character with low power at higher drives. For the parallel driven moving string there is a finite transverse critical depinning force with the depinning transition occuring by the formation of running kinks.Comment: 4 pages, 4 postscript figure

Transverse phase-locking in fully frustrated Josephson junction arrays: a new type of fractional giant steps

We study, analytically and numerically, phase locking of driven vortex lattices in fully-frustrated Josephson junction arrays at zero temperature. We consider the case when an ac current is applied {\it perpendicular} to a dc current. We observe phase locking, steps in the current-voltage characteristics, with a dependence on external ac-drive amplitude and frequency qualitatively different from the Shapiro steps, observed when the ac and dc currents are applied in parallel. Further, the critical current increases with increasing transverse ac-drive amplitude, while it decreases for longitudinal ac-drive. The critical current and the phase-locked current step width, increase quadratically with (small) amplitudes of the ac-drive. For larger amplitudes of the transverse ac-signal, we find windows where the critical current is hysteretic, and windows where phase locking is suppressed due to dynamical instabilities. We characterize the dynamical states around the phase-locking interference condition in the $IV$ curve with voltage noise, Lyapunov exponents and Poincar\'e sections. We find that zero temperature phase-locking behavior in large fully frustrated arrays is well described by an effective four plaquette model.Comment: 12 pages, 11 figure