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

Vibration performance of a lightweight FRP footbridge under human dynamic excitation

This is the author accepted manuscript. The final version is available from Springer via the DOI in this recordFibre-reinforced polymer (FRP) composites are increasingly used as main load bearing materials in design of pedestrian bridges. The FRP footbridges are typically characterised by high strength, and relatively low mass and stiffness. These properties could lead to excessive vibration response under human-induced dynamic loading. This paper studies dynamic performance of a 19.8 m long, simply supported, FRP footbridge exposed to walking and jogging. Moreover, the vibration response of this bridge is compared and critically evaluated against the response of an equivalent, in terms of natural frequency and span length, composite steel-concrete structure. The main factors that drive the vibration performance of the FRP structure are discussed and some recommendations for vibration serviceability checks are made.Engineering and Physical Sciences Research Council (EPSRC

Metod konfigurisanјa upravljačkog sistema otvorene arhitekture rekonfigurabilnog robota za obradu

U radu je prikazan jedan metod konfigurisanja/rekonfigurisanja upravlјačkog sistema otvorene arhitekture rekonfigurabilnih robota za obradu. Na primeru EMC2 upravlјačkog softvera otvorene arhitekture su posredstvom dijagrama za modelovanje dinamičkih procesa definisane aktivnosti sistemintegratora/korisnika u procesu konfigurisanja/rekonfigurisanja upravlјačkog sistema, i uspostavlјene su relacije između softverskih i hardverskih komponenata upravlјanja

Experimental and finite element dynamic analysis of incrementally loaded reinforced concrete structures

This is the author accepted manuscript. the final version is available from Elsevier via the DOI in this recordThis work investigates influence of damage in reinforced concrete (RC) structures on their dynamic properties through modal testing and non-linear finite element (FE) analysis. Five RC beams were designed with the fundamental flexural mode frequencies in the range of 6.5-18.0. Hz for the uncracked state. Mechanical properties of concrete, such as static and dynamic elastic moduli were determined from standard tests and ultra-sonic pulse velocity readings. The beams were incrementally loaded until the span/250 deflection limit was reached and their natural frequencies were measured from the free decay vibrations. The progressive damage reduced fundamental frequencies of tested beams by up to 25%. The non-linear FE analysis was carried out for RC beams and one two-span slab and the calculated reduced frequencies of the 1st and 2nd vibration modes were in excellent agreement with measurements. This led to the conclusion that, given that the non-linear analysis can capture degradation of dynamic stiffness due to cracking, the future dynamic performance and damage identification on the RC structure can be reliably determined from the same FE model. The results reveal potential of the combined modal testing and FE analysis to improve inspection and assessment of the in-service RC structures.University of Warwic

An open architecture control system for multi‐axis wood CNC machining center

Abstract: This paper presents an open architecture control system for multi‐axis wood computer numerical control (CNC) milling machining centre, based on LinuxCNC. The wood CNC machining system is supported by an equivalent virtual machine in a CAD/CAM environment, as well as in the control system. Simulation within virtual environment is essential for multi‐axis machining, and the developed virtual machines are used for program verification and monitoring of the machining process. The virtual machine in the programming system allows the verification of the program before it’s sent to the actual machine, while the virtual machine in the control system represents the final verification of the program, as well as the process monitoring system. Configuration of the control system and implementation of virtual machines will be shown, along with the conducted machining experiments that ensued after the successful simulation on developed virtual machines

Vibration serviceability of a GFRP railway crossing due to pedestrians and train excitation

This is the final version. Available on open access from Elsevier 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 wrap.warwick.ac.uk/136500Glass Fibre-Reinforced Polymers (GFRPs) are a popular option for pedestrian bridges over railway lines as they cause little disruption for installation or maintenance. However, as they are typically lighter and less stiff than traditional materials there is concern about their dynamic response due to human induced actions and train buffeting. Due to a lack of experimental information, further data is needed if such bridges are to be used on future lines, especially with higher speed limits. This paper presents an experimental investigation of the response of a 14.5 m GFRP truss bridge due to pedestrian loading and train induced vibrations. Vibration modes of interest were identified from impact hammer tests. The vibration responses to a range of human loading scenarios, as well as multiple train passes, were measured. The vibration levels remained low under all conditions, demonstrating that this particular type of GFRP bridge is suitable for railway crossings and that further optimisations may be available to designers while meeting vibration serviceability limits. However, consideration of the loadings suggests GFRP bridges may be more susceptible to higher pedestrian harmonics than traditional structures, and that vibrations from train buffeting are likely to be a design consideration for future bridges over high speed lines.Engineering and Physical Sciences Research Council (EPSRC

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

Administrative treatment in the field of subsidies in European Union agriculture in the context of environmental protection

Субвенције у области пољопривреде постају све битнија тема, са изузетно важним последицама. О колико се важној теми ради, указује околност да је у Европској унији усвојена посебна "Заједничка пољопривредна политика" - The Common Agricultural Policy (CAP), као политика око које су све земље чланице постигле сагласност. Пољопривредна политика Европске уније се утврђује на нивоу Уније од стране влада земаља чланица, а спроводи од стране сваке појединачне земље чланице. Политика има за циљ подршку пољопривредницима, како у погледу повећања прихода, тако и у погледу стимулисања производње висококвалитетних производа који се на тржишту траже. Осим тога, пољопривредници се подстичу да истражују нове развојне могућност, између осталог, у погледу еколошки обновљивих извора енергије. Имајући то у виду, од изузетног је значаја адекватно и ефикасно управно поступање и доношење одговарајуће регулативе што омогућава објективну расподелу средстава. Као један од основних механизама у циљу реализације Заједничке пољопривредне политике, посебан акценат ставља се на доделу субвенција пољопривредницима у контексту унапређења пољопривредне праксе која унапређује заштиту животне средине...Agricultural subsidies are becoming increasingly important subject in modern economy, having major influence and consequences for national agricultural production and lives of ordinary citizens of rural areas. The fact that the organization like European Union has its own coherent and harmonized joint agricultural policy – The Common Agricultural Policy (CAP), speaks in favor of the importance of the above topic. The Common Agricultural Policy is being modeled and defined on the level of the European Union by the representatives of the Member State Governments, and is than being implemented by each individual Member State. The said policy is being implemented with view to providing sustainable support to farmers' incomes, while at the same time encouraging agricultural producers to produce high quality products which are the most wanted on the increasingly competitive market, as well as emboldening them to explore additional development opportunities especially in the field of renewable energy. Having the above in mind, it can be underlined that setting up adequate and efficient administrative proceedings and passing appropriate legislation enabling fair disbursement of the subsidies is one of the main goals of the policies in this field. Particular emphasis is being placed on granting subsidies to the agricultural producers who adhere to the established rules, standards and good practices which are beneficial for the climate and environment..

Synthesis, characterization and examination of biological activity of copper(II) complexes with S,O-tetradentate ligands, derivatives of thiosalicylic acid

Uvod: Terapijska primena kompleksa bakra(II) privlači pažnju istraživača zbog mogućnosti koordinovanja sa različitim donorskim atomima. Među liganadima koji u strukturi sadrže sumpor i kiseonik izdvaja se tiosalicilna kiselina, čiji derivati pokazuju citotoksičnost u terapiji tumora. Materijal i metode: U ovoj Doktorskoj disertaciji opisani su sinteza S,O tetradentatnih liganada, derivata tiosalicilne kiseline i kompleksa bakra(II) sa navedenim ligandima. Radi potvrde njihove strukture, sprovedena su različita merenja: mikroanaliza, infracrvena spektroskopija, nuklearno-magnetno-rezonanciona spektroskopija, elektronska paramagnetna rezonancija i molarna provodljivost. U cilju procene biološke aktivnosti sprovedene su nukleofilne supstitucione reakcije kompleksa sa endogenim ligandima (L-metioninom, L-cisteinom i 5’-GMP), in vitro interakcije sa ST-DNK (eng. calf thymus, DNK timusa govečeta) i humanim serumskim albuminom (HSA) pomoću apsorpcione spektroskopske analize i emisione fluorescencije, in silico interakcije sa DNK i HSA. Takođe, primenom MTT kolorimetrijskog testa analizirana je citotoksičnost sintetisanih liganada i kompleksa na tri ćelijske linije. Rezultati: Analizom sprovedenih merenja pretpostavljena je oktaedarska geometrija kompleksa. Svi kompleksi podležu reakcijama nukleofilne supstitucije. Visoke vrednosti konstante vezivanja pokazuju da kompleksi interaguju sa molekulom DNK i HSA. Interakcija sa DNK molekulom dešava se interkalacijom ili interakcijom sa malim žlebom. Kompleksi imaju citotoksični potencijal, dok je prema svim ćelijskim linijama najbolju citotoksičnost na osnovu IC50 vrednosti pokazao kompleks [Cu(S,O-pentilen-tiosalicilna kiselina)].Introduction: The therapeutic application of copper(II)-complexes attracts the attention of researchers due to the possibility of coordination with different donor atoms. Among the ligands that contain sulfur and oxygen in the structure, thiosalicylic acid stands out, whose derivatives show cytotoxicity in tumor therapy. Material and methods: In this Doctoral dissertation, the synthesis of S,O-tetradentate ligands, derivatives of thiosalicylic acid and copper(II)-complexes with the mentioned ligands is described. In order to confirm their structure, various measurements were performed: microanalysis, infrared spectroscopy, nuclear magnetic resonance spectroscopy, electronic paramagnetic resonance and molar conductivity. In order to assess biological activity, nucleophilic substitution reactions of complexes with endogenous ligands (L-methionine, Lcysteine and 5'-GMP), in vitro interactions with ct-DNA (calf thymus DNA) and human serum albumin (HSA) were performed by absorption spectroscopic analysis and emission fluorescence, in silico interactions with DNA and HSA. Also, the cytotoxicity of synthesized ligands and complexes on three cell lines was analyzed using MTT colorimetric test. Results: The octahedral geometry of the complex was assumed by the analysis of the performed measurements. All complexes react to nucleophiles. High values of the binding constant indicate that the complexes interact with the DNA molecule and HSA. Interaction with a DNA molecule occurs by intercalation or interaction with a small groove. The complexes have cytotoxic potential, while the [Cu (S,O-pentylene-thiosalicylic acid)] complex showed the best cytotoxicity based on IC50 values according to all cell lines. Keywords: S,O-tetradentate ligands, copper(II) complexes, interactions, molecular docking, antitumor activit

Effects of pedestrian excitation on two short-span FRP footbridges in Delft

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordReported in this paper is an evaluation of the vibration behaviour of two footbridges in The Netherlands having main spans of about 15, m. Short-span footbridges over canals and rivers are embedded in the landscape of Delft and elsewhere. Increasingly, these bridges are made of Fibre-Reinforced Polymer (FRP) composites, utilising the high-strength and light-weight nature of the material, and taking advantage of fast installation and low maintenance costs. Due to low mass, these FRP bridges might be sensitive to dynamic excitation by human actions. The two footbridges investigated in this paper have the main bearing structure which consists of either two or four longitudinal beams made of vacuum infused FRPs with foam cores connected by an FRP deck. Modal testing revealed that fundamental vertical natural frequency of the two structures at 4.8 and 6.1, Hz is in the range typical of similar structures made of concrete and steel, whilst the corresponding damping ratio for the wider, slightly cambered, bridge was exceptionally high at 7.9%. The vibration response to dynamic force by people walking was typically up to 1, m/s 2 . While both of these light-weight structures performed satisfactorily under the regular pedestrian loading, the higher frequency – higher damping structure represents an example of successful control of pedestrian-induced vibrations by means of longitudinal restraints at the end supports and slightly curved shape of the main structure.Engineering and Physical Sciences Research Council (EPSRC