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'�rosion de ponts est un ph�nom�ne extr�mement complexe � cause des caract�ristiques al�atoires du courant charg� de s�diments � proximit� des piliers et des but�es. Cet �v�nement am�ne de grandes incertitudes et des risques incontournables dans la conception de piliers et de but�es de ponts. En cela, un mod�le de fiabilit� mixte a �t� d�velopp� afin d'�valuer la fiabilit� contre l'�rosion des piliers de ponts en utilisant une r�sistance statique � interf�rence de charge. Bas� sur l'interpr�tation physique du ph�nom�ne et une analyse statistique de l'information disponible, la profondeur d'�rosion maximale relative (correspondant � l'�l�vation minimale requise des fondations de piliers) et la combinaison lin�aire de la profondeur relative du courant suivant le nombre de Froude sont d�finis comme la r�sistance du syst�me et la charge externe, respectivement. En examinant une s�rie de donn�es obtenues en laboratoire et sur le terrain, une distribution lognormale bivari�e � deux param�tres a �t� trouv�e pour repr�senter la fonction de densit� de probabilit� conjointe de la r�sistance et de la charge. Des expressions de fiabilit� ont �t� d�velopp�es en termes de r�sistance. L'utilisation du mod�le est illustr�e dans une application pratique o� une relation est obtenue entre la fiabilit� et les facteurs de s�curit� pour diff�rentes p�riodes de retour. Cette information est d'importance dans le processus de d�cision.Mots cl�s : fiabilit�, pilier de pont, �rosion, r�sistance, chargement, facteur de s�curit�, p�riode de retour.[Traduit par la R�daction]


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