Short NoteParametric study on the aerodynamic stability of a long-span suspension bridge
Introduction
Suspension bridge, which consists of the deck, main cables, hangers, towers and anchors, etc., is an old bridge structure, and becomes an important type of the cable-supported bridges. Until now, it is still the competitive scheme of the bridges whose spans exceed 1000 m. Currently, the longest suspension bridge is the Akashi Kaikyo bridge in Japan with a main span of 1990 m. In the 21st century, many engineering projects across the straits are being planned around the world, and a lot of long-span particularly super long-span suspension bridges are schemed, for example, the Messina strait bridge with a main span of 3300 m and the Gibraltar bridge with a main span of 5000 m. The increase in span length combined with the trend to more shallow or slender decks in suspension bridges has raised concern on their behaviors under the service and environmental dynamic loadings such as the traffic, wind and earthquake loadings. Among them, more attentions have been paid to the wind stability for the design and construction of long-span suspension bridges.
Comprehensive investigations have been done on the static and dynamic behaviors of long-span suspension bridges under the dead load, traffic and static wind loading, etc, [1], [2], [3], [4], [5], [6]. The effects of some design parameters on the static performance such as structural system, the cable sag, the side span length, the depth, dead load and supporting system of the deck, etc have been studied. However, few investigations have been made concerning the influence of these parameters on the aerodynamic stability of long-span suspension bridges. Actually, besides the static performance, the dynamic characteristics and further the aerodynamic stability will be affected by theses parameters. Therefore, the effects of these design parameters on the aerodynamic stability of long-span suspension bridges needs to be further investigated.
In this paper, based on the method of three-dimensional nonlinear aerodynamic stability analysis developed by Zhang [7], [8], in which the geometric nonlinearity of bridge structures and the effects of nonlinear wind–structure interaction are considered, parametric analyses on the aerodynamic stability of the Runyang bridge over the Yangtze River are carried out, some design parameters that have significant influence on the aerodynamic stability of long-span suspension bridges are pointed out, and the favorable structural system of the bridge is also discussed on the basis of the wind stability.
Section snippets
Description of the Runyang bridge over the Yangtze river
The Runyang bridge is the longest suspension bridge under construction in China. The bridge has a center span of 1490 m and two side spans of 470 m as shown in Fig. 1. Fig. 2 shows the bridge deck, which is a streamlined steel box girder of 35.9 m wide and 3.0 m high. The towers are door-shaped with 209 m height. The sag to span length ratio is the distance between the two cables is 34.3 m, and the spacing of hangers is 16 m. The member sectional parameters of the bridge are given in Table 1.
Parametric analyses
The aerodynamic stability analysis is performed on a three-dimensional finite element model of the bridge, which includes 148 beam elements modeling the deck and towers, 374 bar elements modeling the cables and hangers, and 182 rigid arm elements modeling the diaphragms of the deck. The aerostatic coefficients and flutter derivatives at different wind angles of attack are obtained from the section-model tests of the bridge [9]. Structural damping is assumed as 0.5%.
Concluding remarks
Based on the method of nonlinear aerodynamic stability analysis, parametric studies have been done on the Runyang bridge over the Yangtze River, the effects of some design parameters on the aerodynamic stability are investigated. Some important conclusions can be summarized as follows:
- (1)
As far as the aerodynamic stability is concerned, the three-span system and the continuous deck are confirmed analytically to be aerodynamically favorable for the bridge.
- (2)
The short side span is advantageous to the
Acknowledgements
This project is supported by Zhejiang Provincial Science Foundation of China and China Postdoctoral Science Foundation, which are gratefully acknowledged.
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