Proper Orthogonal Decomposition for simulating the alongwind Equivalent Static Force of long-span bridges

This paper develops and discusses a method by which it is possible to evaluate the Equivalent Static Force (ESF) of wind in the case of long-span bridges. Attention is focused on the alongwind direction. The study herein carried out deals with the classical problems of determining the maximum effects due to the alongwind action and the corresponding ESFs. In order to derive the wind-induced effects acting on the deck, the Gust Effect Factor (GEF) technique is extended to long-span bridges. By adopting the GEF technique, it is possible to define the ESF that applied on the structure produces a specified maximum effect. Nevertheless in the case of long-span bridges the application of the ESF associated to a specified maximum effect does not furnish the correct maximum values of other wind-induced effects acting on the deck. Based on this observation, a new technique is proposed which allows to define an ESF able to simultaneously reproduce the maximum alongwind effects of the bridge deck. The proposed technique is based on the GEF and the Proper Orthogonal Decomposition (POD) techniques and represents a valid instrument of research for the understanding of the wind excitation mechanism.