D. Bryja

Random vibration of a suspension bridge due to highway traffic

The problem of dynamic non-linear response of a suspension bridge to the passage of a train of concentrated forces with random weight is considered. Force arrivals at the bridge are assumed to constitute a Poisson process of events. Thus, the excitation process idealizes vehicular traffic loads on a bridge. By use of both iterative and linearization methods the solution for the expected value and variance of the bridges deflections is determined. As an example, the response of a bridge to a stationary stream of forces is obtained. A numerical technique is developed to compute the solution for a particular bridge and some practical cases of the loading.

Stochastic response analysis of suspension bridge under gusty wind with time-dependent mean velocity

The paper presents a general outline of the method of stochastic response analysis of suspension bridge subjected to randomly fluctuated wind with time-dependent mean velocity. The proposed method is aimed to examine how the repeatable wind gusts affect bridge vibrations and to investigate amplified bridge response in resonant regimes. First, a non-homogeneous wind velocity model and associated buffeting forces are developed. The buffeting forces are derived under the general assumption that their span-wise correlation is the same as that of incoming wind fluctuations. Next, a bridge deck is divided into sections along span, and the dynamic bridge response is obtained with neglecting structure nonlinearities, by summing up component responses due to sectional buffeting forces. For the correlation response analysis an analytical time-domain approach based on stochastic calculus is suggested. The mean function and covariance function of bridge response are derived in the general case where in-time correlation of wind velocity fluctuations results from a given wind spectrum. Additionally, for a tentative estimation, two approximate formulas for variance of bridge response are obtained using two opposing mathematical idealizations of wind correlation in time. In the last part, numerical application of the proposed procedure is presented and advantages in bridge engineering are discussed.