Quantification of dynamic excitation potential of pedestrian population crossing footbridges

Due to their slenderness, many modern footbridges may vibrate significantly under pedestrian traffic. Consequently, the vibration serviceability of these structures under human-induced dynamic loading is becoming their governing design criterion. Many current vibration serviceability design guidelines, concerned with prediction of the vibration in the vertical direction, estimate a single response level that corresponds to an "average" person crossing the bridge with the step frequency that matches a footbridge natural frequency. However, different pedestrians have different dynamic excitation potential, and therefore could generate significantly different vibration response of the bridge structure. This paper aims to quantify this potential by estimating the range of structural vibrations (in the vertical direction) that could be induced by different individuals and the probability of occurrence of any particular vibration level. This is done by introducing the inter- and intra-subject variability in the walking force modelling. The former term refers to inability of a pedestrian to induce an exactly the same force with each step while the latter refers to different forces (in terms of their magnitude, frequency and crossing speed) induced by different people. Both types of variability are modelled using the appropriate probability density functions. The probability distributions were then implemented into a framework procedure for vibration response prediction under a single person excitation. Instead of a single response value obtained using currently available design guidelines, this new framework yields a range of possible acceleration responses induced by different people and a distribution function for these responses. The acceleration ranges estimated are then compared with experimental data from two real-life footbridges. The substantial differences in the dynamic response induced by different people are obtained in both the numerical and the experimental results presented. These results therefore confirm huge variability in different people's dynamic potential to excite the structure. The proposed approach for quantifying this variability could be used as a sound basis for development of new probability-based vibration serviceability assessment procedures for pedestrian bridges

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

Increasing 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

Comparison of multidetector-row computed tomography and duplex Doppler ultrasonography in detecting atherosclerotic carotid plaques complicated with intraplaque hemorrhage [Usporedba višeslojne kompjuterizirane tomografije i duplex Doppler ultrazvuka u otkrivanju aterosklerotskih karotidnih plakova kompliciranih krvarenjem u plak ]

This study compared sensitivity and specificity of multidetector-row computed tomography and duplex Doppler ultrasonography in detecting atherosclerotic carotid plaques complicated with intraplaque hemorrhage. Carotid plaques from 50 patients operated for carotid artery stenosis were analyzed. Carotid endarterectomy was performed within one week of diagnostic evaluation. Results of multidetector-row computed tomography and duplex Doppler ultrasonography diagnostic evaluation were compared with results of histological analysis of the same plaque areas. American Heart Association classification of atherosclerotic plaques was applied for histological classification. Median tissue density of carotid plaques complicated with intraplaque hemorrhage was 14.7 Hounsfield units. Median tissue density of noncalcified segments of uncomplicated plaques was 54.3 Hounsfield units (p = 0.00003). The highest tissue density observed for complicated plaques was 31.8 Hounsfield units. Multidetector-row computed tomography detected plaques complicated with hemorrhage with sensitivity of 100% and specificity of 70.4%, with tissue density of 33.8 Hounsfield units as a threshold value. Duplex Doppler ultrasonography plaque analysis based on visual in-line classification showed sensitivity of 21.7% and specificity of 89.6% in detecting plaques complicated with intraplaque hemorrhage. Multidetector-row computed tomography showed a very high level of sensitivity and a moderate level of specificity in detecting atherosclerotic carotid plaques complicated with hemorrhage. Duplex Doppler ultrasonography plaque analysis based on visual in-line classification showed a low level of sensitivity and a moderate-high level of specificity in detecting atherosclerotic carotid plaques complicated with hemorrhage

Darko Polšek, Zapisi iz treće kulture

Prikaz knjige Darko Polšek, Zapisi iz treće kulture, Naklada Jesenski i Turk, Zagreb 2003, 326 str

The antioxidative protecting role of the Mediterranean diet [Antioksidativno protektivno djelovanje mediteranske dijete]

Recent meta-analysis shows that adherence to a Mediterranean diet (MD) can significantly decrease the risk of overall mortality, mortality from cardiovascular diseases, as well as incidence of mortality from cancer, and incidence of Parkinson's and Alzheimer's disease. All of these diseases could be linked to oxidative stress (OS) as antioxidative effect of MD is getting more attention nowadays. Although a lot of research has been done in this area and it suggests antioxidative protective role of MD, the presented evidence is still inconclusive. The aim of this paper is to review studies investigating the effect of MD on OS, as well as to identify the areas for further research

Zwischen den Welten : antike Kulturlandschaften im Illyricum

Das Wissen um eine antike Kultur ist nicht selten vom Stand der modernen Forschung geprägt. Auf dem Gebiet der Erforschung des antiken Westbalkan hat dieser keineswegs ein Optimum erreicht. Vielmehr haben der politische Umbruch in Osteuropa sowie die Kriege seit den 1990er Jahren in den Nachfolgestaaten des ehemaligen Jugoslawien ein negatives Licht auf jene Länder und seine Menschen geworfen. Diese Bewertung wird darüber hinaus bis in die heutigen Tage paradoxerweise auch auf die Kulturen der Antike übertragen. Dabei bildet die Region an der Adria mit ihren archäologischen Denkmälern aus verschiedenen Jahrtausenden der Menschheitsgeschichte eine der ältesten Kulturlandschaften Europas. In kaum einem anderen Teil des Kontinents finden sich Natur und Kultur derart eng beieinander. Die in albanischer, serbischer, kroatischer oder slowenischer Sprache verfassten wissenschaftlichen Abhandlungen sowie die von den Touristenrouten häufig abseits gelegenen Kulturgüter sind darüber hinaus in Westeuropa zumeist unbekannt. Aus diesem Grund soll dieser Aufsatz einen Beitrag zum kulturellen „Wiederaufbau“ des am Adriatischen Meer und im Dinarischen Gebirge gelegenen antiken Illyricum leisten. Zunächst wird zur allgemeinen Orientierung der geographische Rahmen abgesteckt. Des weiteren soll die geographische sowie topographische Situation der verschiedenen Kulturlandschaften entlang der Adria sowie des Dinarischen Hinterlandes exemplarisch aufgezeigt werden. Schließlich wird versucht, die sowohl historische als auch archäologische „Lücke“ zwischen Griechenland und Italien für die vorrömische Zeit zu schließen