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

Reliability of Assessment Criteria for Building Floor Vibrations Under Human Excitation

Conference paperVibration serviceability of floor structures under internal human excitations is a key criterion that determines the acceptability or otherwise of both new-build structures and those that have been altered or subjected to a change of use. To assist structural engineers in the design of such floors and the assessment of the vibration environment, there are a number of guidelines and standards that propose limits for various occupancies. This paper focuses on vibration serviceability of office floors under human excitation and examines actual responses acquired from whole day monitoring of four typical office floor structures. The reliability of the limits proposed in the various guidance documents is assessed, with the key conclusions that limits based on R factors are not particularly reliable and assessments on the basis of vibration dose values are more reliable but the currently specified limit in BS6472 may be too high.Engineering and Physical Sciences Research Council (EPSRC

Dynamic loading factors of individual jogging forces

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

Number of successive cycles necessary to achieve stability of selected ground reaction force variables during continuous jumping.

Journal ArticleAuthor's manuscript version. The final published version is available from the publisher via: http://www.jssm.org/research.php?id=jssm-08-639.xml. This is an open access journal.Because of inherent variability in all human cyclical movements, such as walking, running and jumping, data collected across a single cycle might be atypical and potentially unable to represent an individual's generalized performance. The study described here was designed to determine the number of successive cycles due to continuous, repetitive countermovement jumping which a test subject should perform in a single experimental session to achieve stability of the mean of the corresponding continuously measured ground reaction force (GRF) variables. Seven vertical GRF variables (period of jumping cycle, duration of contact phase, peak force amplitude and its timing, average rate of force development, average rate of force relaxation and impulse) were extracted on the cycle-by-cycle basis from vertical jumping force time histories generated by twelve participants who were jumping in response to regular electronic metronome beats in the range 2-2.8 Hz. Stability of the selected GRF variables across successive jumping cycles was examined for three jumping rates (2, 2.4 and 2.8 Hz) using two statistical methods: intra-class correlation (ICC) analysis and segmental averaging technique (SAT). Results of the ICC analysis indicated that an average of four successive cycles (mean 4.5 ± 2.7 for 2 Hz; 3.9 ± 2.6 for 2.4 Hz; 3.3 ± 2.7 for 2.8 Hz) were necessary to achieve maximum ICC values. Except for jumping period, maximum ICC values took values from 0.592 to 0.991 and all were significantly (p ≤ 0.05) different from zero. Results of the SAT revealed that an average of ten successive cycles (mean 10.5 ± 3.5 for 2 Hz; 9.2 ± 3.8 for 2.4 Hz; 9.0 ± 3.9 for 2.8 Hz) were necessary to achieve stability of the selected parameters using criteria previously reported in the literature. Using 10 reference trials, the SAT required standard deviation criterion values of 0.49, 0.41 and 0.55 for 2 Hz, 2.4 Hz and 2.8 Hz jumping rates, respectively, in order to approximate the ICC results. The results of the study suggest that the ICC might be a less conservative but more objective method to evaluate stability of the data. Based on these considerations, it can be recommended that a force time history due to continuous, repetitive countermovement jumping should include minimum of four (the average from the ICC analysis) and possibly as many as nine successive jumping cycles (the upper limit of the ICC analysis) to establish stable mean values of the selected GRF data. This information is important for both experimental measurements and analytical studies of GRF signals due to continuous, repetitive countermovement jumping. Key pointsThe number of successive jumping cycles due to continuous, repetitive countermovement jumping obtained from a test subject during in a single testing session influences the stability of the corresponding ground reaction force variables on a cycle-by-cycle basis.Researchers have used different criteria and methods for determining stability of ground reaction force data for a variety of activities, making comparisons among studies and activities difficult.In the present study, segmental averaging technique indicated that an average of ten successive jumping cycles were necessary to achieve stability of the selected force parameters using criteria previously reported in the literature, while less conservative test-retest intra-class correlation (ICC) analysis showed that an average of four successive jumping cycles were necessary for stability.Based on these considerations, it can be recommended that a force time history due to continuous, repetitive countermovement jumping should include minimum of four (the average from the ICC analysis) and possibly as many as nine successive jumping cycles (the upper limit of the ICC analysis) to achieve stability of jumping force data on a cycle-by-cycle basis.Knowledge about the stability of jumping force data is an important to maximize reliability of their experimental and analytical characterizations.Engineering and Physical Sciences Research Council (EPSRC

Vibration serviceability of footbridges under human-induced excitation: a literature review

issue: 1-2articleIncreasing strength of new structural materials and longer spans of new footbridges, accompanied with aesthetic requirements for greater slenderness, are resulting in more lively footbridge structures. In the past few years this issue attracted great public attention. The excessive lateral sway motion caused by crowd walking across the infamous Millennium Bridge in London is the prime example of the vibration serviceability problem of footbridges. In principle, consideration of footbridge vibration serviceability requires a characterisation of the vibration source, path and receiver. This paper is the most comprehensive review published to date of about 200 references which deal with these three key issues. The literature survey identified humans as the most important source of vibration for footbridges. However, modelling of the crowd-induced dynamic force is not clearly defined yet, despite some serious attempts to tackle this issue in the last few years. The vibration path is the mass, damping and stiffness of the footbridge. Of these, damping is the most uncertain but extremely important parameter as the resonant behaviour tends to govern vibration serviceability of footbridges. A typical receiver of footbridge vibrations is a pedestrian who is quite often the source of vibrations as well. Many scales for rating the human perception of vibrations have been found in the published literature. However, few are applicable to footbridges because a receiver is not stationary but is actually moving across the vibrating structure. During footbridge vibration, especially under crowd load, it seems that some form of human–structure interaction occurs. The problem of influence of walking people on footbridge vibration properties, such as the natural frequency and damping is not well understood, let alone quantified. Finally, there is not a single national or international design guidance which covers all aspects of the problem comprehensively and some form of their combination with other published information is prudent when designing major footbridge structures. The overdue update of the current codes to reflect the recent research achievements is a great challenge for the next 5–10 years

A spectral density approach for modelling continuous vertical forces on pedestrian structures due to walking

Existing walking models used for vibration serviceability assessment of structures carrying pedestrians are typically based on measurements of single footfalls replicated at precise intervals. This assumed perfect periodicity allows walking forces to be modelled as a Fourier series based on the walking pace and its integer multiples. This paper examines real continuous walking forces obtained from an instrumented treadmill and the effect of their random imperfections through time simulations of structural response and shows that there are significant differences between responses due to the imperfect real walking forces and the equivalent perfectly periodic simulation. These differences are most significant for higher harmonics where the simulated vibration response is overestimated. As a realistic representation of imperfect walking is an auto-spectral density function, the random character naturally leads to a stochastic approach to treatment of pedestrian loading applied in the frequency domain. The approach can be used for single pedestrians as well as crowd loading where correlation between pedestrians as well as statistics of their pacing rates is used

Nonstructural partitions and floor vibration serviceability

Author's accepted manuscript. The final published version is available from the publisher via DOI: 10.1061/(ASCE)AE.1943-5568.0000171. © 2015 American Society of Civil Engineers.Non-structural vertical partitions and cladding can have a significant effect on the vibration serviceability of floor systems. A typical modern office building, consisting of steel-concrete composite floor systems, was created to investigate the potential beneficial effects of integrating non-structural partitions into structural floor systems to reduce floor vibrations due to walking excitation. Two models of this building were presented, one to represent the completed building with an open-plan layout and another with partitions added in a beneficial pattern to enhance the floor's vibration performance. The addition of non-structural partitions successfully reduced floor accelerations due to walking excitation and helped the floor to satisfy the vibration serviceability criterion for office floors. The potential of vertical full-height non-structural partitions and cladding to transmit vibrations between floors was also investigated. A vibration transmission simulation was conducted on the 2 2 Finite Element (FE) model to quantify vibration transmission between floors through the structural frame and non-structural vertical partitions and cladding. The results were then compared with experimental results previously recorded on the floors of a real-life Charles Institute building in Dublin featuring the same type of partitions but different structural frame. It was concluded that both the FE model and real-life building featuring structural elements and full-height partitions have the potential to transmit significant level of vibrations between two adjacent floors. The results presented in this study will be of interest to design engineers and researchers in the area of vibration serviceability of floor systems, as it highlights the potential of non-structural elements to reduce the floor vibration response to acceptable levels to transmit vibrations between floors.Irish Research Council for Science, Engineering and Technology (IRCSET)Engineering and Physical Sciences Research Council (EPSRC

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

Novel Quorum Quenching YtnP Lactonase From Bacillus paralicheniformis Reduces Pseudomonas aeruginosa Virulence and Increases Antibiotic Efficacy in vivo

Bacterial infections have become increasingly difficult to treat due to the occurrence of antibiotic-resistant strains. A promising strategy to increase the efficacy of therapy is to combine antibacterials with agents that decrease pathogen virulence via the modulation of the quorum sensing (QS). Lactonases inhibit acylated homoserine lactone (AHL)-mediated QS in Gram-negative bacteria, including the leading nosocomial pathogen Pseudomonas aeruginosa. Here we describe the characteristics of heterologously expressed YtnP lactonase from Bacillus paralicheniformis ZP1 (YtnP-ZP1) isolated from agricultural soil using the culture enrichment method. Purified YtnP-ZP1 hydrolyzed different AHLs with preference to substrates with long acyl residues as evaluated in assays with biosensors and HPLC. The enzyme showed good thermostability and activity in a wide temperature range. YtnP-ZP1 in 50 μg mL–1 concentration reduced the amount of P. aeruginosa-produced long-chain AHLs by 85%, while it hydrolyzed 50% of short-chain AHLs. Incubation of P. aeruginosa PAO1 with YtnP-ZP1 reduced its swarming motility and elastolytic activity without bactericidal effect. YtnP-ZP1 caused the inhibition of biofilm formation and disintegration of mature biofilms in P. aeruginosa PAO1 and multiresistant clinical strain BR5H that was visualized by crystal violet staining. The treatment with YtnP-ZP1 in concentrations higher than 25 μg mL–1 improved the survival of P. aeruginosa PAO1-infected zebrafish (Danio rerio), rescuing 80% of embryos, while in combination with tobramycin or gentamicin survival rate increased to 100%. The treatment of P. aeruginosa PAO1 biofilms on infected zebrafish tail wounds with 50 μg mL–1 YtnP-ZP1 and 2 × MIC tobramycin led to infection clearing in 2 days. The extensive toxicity studies proved YtnP-ZP1 was non-toxic to human cells and zebrafish. In conclusion, novel YtnP-ZP1 lactonase with its effective anti-virulence activity could be used to increase the efficacy of clinically approved antibiotics in clearing both systemic and biofilm-associated P. aeruginosa infections

Antiplasmodial activity and in vivo bio-distribution of chloroquine molecules released with a 4-(4-ethynylphenyl)-triazole moiety from organometallo-cobalamins

We have explored the possibility of using organometallic derivatives of cobalamin as a scaffold for the delivery of the same antimalarial drug to both erythro- and hepatocytes. This hybrid molecule approach, intended as a possible tool for the development of multi-stage antimalarial agents, pivots on the preparation of azide- functionalized drugs which, after coupling to the vitamin, are released with a 4-(4- ethynylphenyl)-triazole functionality. Three chloroquine and one imidazolopiperazine derivative (based on the KAF156 structure) were selected as model drugs. One hybrid chloroquine conjugate was extensively studied via fluorescent labelling for in vitro and in vivo bio-distribution studies and gave proof-of-concept for the design. It showed no toxicity in vivo (zebrafish model) as well as no hepatotoxicity, no cardiotoxicity or developmental toxicity of the embryos. All 4-(4-ethynylphenyl)-triazole derivatives of chloroquine were equally active against chloroquine-resistant (CQR) and chloroquine- sensitive (CQS) Plasmodium falciparum strains