No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Dynamic characteristics of cable trussed bridges
Abstract
Cable trussed bridges have comparatively slender girders, a king post, and external cables anchored at both ends of the girders. The combination of a post and the cables acts as an elastic support for the girders in the middle of the span. In steep valleys, this type of bridge is more economical to build. This paper describes the dynamic characteristics, aerodynamic stability, seismic stability, and traffic-response of cable trussed bridges.
In this experimental study, fluid dynamic response characteristics of wake galloping between two square prisms of same size in tandem and staggered arrangement to their relative position and free stream velocity were investigated. An immovable square prism of size d was fixed at upstream side and another vibratile square prism was placed at downstream side. The relative position of the vibratile downstream prism to the upstream prism was varied in the range from 1.6 d to 3.1 d in stream-wise direction, and in the range from 0.0 d to 2.1 d in cross flow direction. The vibratile prism at downstream side is elastically supported at it's both end and is ristricted to vibrate in only cross-flow direction. Instantaneous displacement of vibratile prism was measured by means of Laser Displacement Anemometer, and degree of vibration was evaluated by rms value of the fluctuating displacement. At first, response characteristics of wake galloping to relative position and flow velocity were investigated by free-vibration experiments in tandem and staggered arrangements using a wind tunnel. From the experiments, it was found that the response characteristics can be classified into three patterns in relation to relative positions and free stream velocities. Then the wake galloping phenomena occurred in the free-vibration experiments were reproduced by forced-vibration experiments in a water channel to conduct flow visualization. The visualization results well explained the phenomena observed in the wind tunnel experiment.
The instrumentation of special structures such as large bridges, tunnels, monuments etc., contributes towards a better understanding
of their dynamic performance, as well as a more accurate and reliable prediction of the earthquake resistance of such large-scale
structures. In experimental analysis the classical ways to estimate the modal parameters of the whole structural system, as
well as of its structural elements, is either to excite the structure artificially (using, e.g. vibrators, heavy vehicles)
or to evaluate the recordings obtained from a weak or strong ground motion. In modeling the behaviour of a civil engineering
structure in a realistic way, among the important parameters to be defined are the mass distribution, the damping characteristics,
the stiffness of the main load resisting system, the influence of secondary elements and interaction phenomena. Large vibration
tests provide reliable data for the evaluation of the influence of such modal parameters. The effective analytical evaluation
of the bridge through reliable and effective numerical models is necessary in order to verify the experimental data. By comparing
the results of both experimental and analytical approaches and adequately updating the analytical model, a more realistic
modeling of the bridge can be obtained. Changes in the modal parameters during the time-life of the bridge can contribute
towards detection of damages, such as crackings or any other reasons reducing the stiffness of the structural system. The
cable-stayed bridge in Evripos channel (Greece) was selected to apply the aforementioned methodology. The main ambient vibrations
recorded are due to traffic, wind and moderate earthquakes at small distances from the bridge. Three-dimensional finite element
models of the bridge were created and the dynamic behaviour of the bridge was analysed for both a small and a strong earthquake
with high frequency content. Results of the experimental estimation of eigenvalues of the vibration modes are also presented.
Finally, comparisons between experimental and analytical values have been performed,
ResearchGate has not been able to resolve any references for this publication.