Time simulation of aerodynamic response of long-span bridges to turbulent wind

Abstract

An efficient computational procedure is developed for time simulation of buffeting and flutter response of suspension bridges. The structural model is reduced by quasi-static condensation leading to a typical 1:5 reduction of the number of dynamic degrees of freedom. The turbulent wind field is represented by a convected fully three-dimensional velocity field and simulated by an auto-regressive procedure in which the coefficients are determined explicitly from conditional mean values and variances in the convected field. This procedure permits free choice of the simulation points – typically the nodes of the structural model. The convection concept can include translation of a fully three-dimensional nodal lay-out, e.g. the double set of main cables and hangers. The wind field representation is a generalized orthotropic representation of the von Kàrmàn velocity spectrum. This implies that the coherence functions contain a length scale in addition to the traditional non-dimensional frequency, reducing the coherence at large separations and thereby the fluctuating response of long suspension bridges. The aerodynamic forces are represented by a compact rational representation which is included in a momentum based time integration procedure which allows a fairly detailed tailoring of structural and algorithmic damping. The procedure is sufficiently general to permit response analysis of the full bridge structure with two layers of cables, but examples demonstrate rather small effects on the lower modes from the wind load on the cables.