Composite reliability model for local scour around cylindrical bridge piers

Yanmaz, A Melih; Cicekdag, Ozgur
June 2001
Canadian Journal of Civil Engineering;Jun2001, Vol. 28 Issue 3, p520
Academic Journal
Bridge scour is an extremely complex phenomenon because of the random characteristics of sediment laden flow in close proximity to piers and abutments. This occurrence leads to high uncertainties and unavoidable risk in bridge pier and abutment design. In this study, a composite reliability model is developed for the reliability assessment of bridge pier scour using static resistance – loading interference. Based on the physical interpretation of the phenomenon and a statistical analysis of the available information, the relative maximum scour depth (corresponding to the minimum required relative pier footing elevation) and the linear combination of the relative approach flow depth and flow Froude number are defined as the system resistance and external loading, respectively. By examining a set of laboratory and field data, a two-parameter bivariate lognormal distribution is found to represent the joint probability density function of resistance and loading. Reliability expressions are developed in terms of resistance. Use of the model is illustrated in a practical application in which a relationship is obtained between the reliability and safety factors under various return periods. This information is of importance in decision making.Key words: reliability, bridge pier, scour, resistance, loading, safety factor, return period.L'érosion de ponts est un phénomène extrêmement complexe à cause des caractéristiques aléatoires du courant chargé de sédiments à proximité des piliers et des butées. Cet événement amène de grandes incertitudes et des risques incontournables dans la conception de piliers et de butées de ponts. En cela, un modèle de fiabilité mixte a été développé afin d'évaluer la fiabilité contre l'érosion des piliers de ponts en utilisant une résistance statique – interférence de charge. Basé sur l'interprétation physique du phénomène et une analyse statistique de l'information disponible, la profondeur d'érosion maximale relative (correspondant à l'élévation minimale requise des fondations de piliers) et la combinaison linéaire de la profondeur relative du courant suivant le nombre de Froude sont définis comme la résistance du système et la charge externe, respectivement. En examinant une série de données obtenues en laboratoire et sur le terrain, une distribution lognormale bivariée à deux paramètres a été trouvée pour représenter la fonction de densité de probabilité conjointe de la résistance et de la charge. Des expressions de fiabilité ont été développées en termes de résistance. L'utilisation du modèle est illustrée dans une application pratique où une relation est obtenue entre la fiabilité et les facteurs de sécurité pour différentes périodes de retour. Cette information est d'importance dans le processus de décision.Mots clés : fiabilité, pilier de pont, érosion, résistance, chargement, facteur de sécurité, période de retour.[Traduit par la Rédaction]


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