| doi:10.3850/978-981-08-6218-3_BS-Th029 |
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DESIGN AND RESEARCH OF A SPATIAL CABLE NETS SUPPORTED BRIDGE
Wenliang Qiua, Zhe Zhangb and Yonggang Tanc
School of civil engineering, Dalian University Technology, Dalian, PR China.
aQWL2002@263.net
bZHANGZHE@dlut.edu.cn
cTANYG@dlut.edu.cn
EXTENDED ABSTRACT
Dalian Xinhai Bay Bridge is a cable net steel bridge with a single inclined tower in Dalian city of China. This bridge uses spatial cable nets to support the steel box beam. One end of the main cable of main span is anchored to one end of the beam to form a semi-self-anchored structure. After introducing the design of the bridge, this paper presents an analytical method for determination of the shape and internal forces of the cable net structure. Because the structure is complicated in mechanics and construction, a scale model is made in laboratory to simulate the whole construction process and the stress conditions of the model are tested during construction and at completion stage. Finally, the static and dynamic load experiments are performed to test the completed bridge.
1. INTRODUCTION
Xinghai Bay Bridge is located in the east of Dalian Xinghai Square which spans Malan River near the sea. It is a self-anchored suspension bridge with span length of 134.4m. The most special characteristic of the bridge is that it has a reticulate cable system looking like fishing net. This bridge has been opened to traffic in August 2006 and become a beautiful scene in Dalian city.
Because the bridge is a complicated space flexural structure, it has many difficult problems in design and construction. In this paper, the methods to determine the cable configuration and stress condition of the bridge, model test in laboratory, process of construction and loading test of the completed structure are presented.
2. DETERMINATION OF TENSION HANGER TENSION AND CABLE CONFIGURATION
For this bridge, there are vertical hangers and inclined hangers that make the bridge not similar as the normal suspension. The tension forces of hanger not only determine the mechanical condition of the whole bridge, but also determine the configuration of the cable system. Considering the hump of the stiffening girder of self-anchored suspension bridge can be deduced the tension of hangers by the horizontal components of cable forces, the tension forces of vertical hangers and inclined hangers are determined.
In order to determine the configuration of the cable system subjected by vertical hangers and inclined hangers, a new analytical segmental catenary curve method is derived. Using the segmental catenary curve method and the tensions of hangers determined previously, the configuration of the main cable system can be determined. For comparison, the calculated result calculated by nonlinear finite element method (FEM) is also given. It is found that the two calculated results are nearly same with maximal difference of 0.8mm.
3. MODEL TEST
Considering the structure and construction of Xinghai Bay Bridge are very complicated, in order to check correctness of the calculated results and study the construction method, a 1:25 model of the bridge in laboratory is used for simulating the process of construction and static and dynamic load test. The experiences obtained from the model test are used in the design and construction of the bridge, and it is found that they made the construction very safe and convenient.
4. CONSTRUCTION
The Xinghai Bay Bridge located at the entrance of Malan River, so barges can be used to erect the girder and tower. The tower is prefabricated on the bank. It is carried to the bridge site and placed on the temporary piers. Then it is vertically rotated to the design position by the barge. The girder is separated to 3 segments to be prefabricated on the bank. After erection of tower, the three girder segments are carried to the bridge site and placed on the temporary piers. Then they are welded to be whole girder.
To make the position of cable bands correct and simplify the construction, before erection of main cables, the main cables are connected together and the hangers are fixed on cables by cable bands on the girder.
5. EXPERIMENT ON COMPLETED BRIDGE
To further verify the correctness of the calculated results, static and dynamic load tests are performed on the completed bridge before it is put in use.
The measured items of static experiments include deformation of girder and tower and stress of the girder. Four trucks with weight of about 20 tons are used as static loads for the experiments. The measured values agree with the calculated values very well.
The purpose of dynamic experiment is to measure the characteristics of free vibration of the completed bridge. Some acceleration sensors are fixed on the deck to sample the vibrating signal excited by ground motion and environmental jamming. The mode shape, frequency and damping ratio can be obtained from the sampled signal. It is found that the measured values of vibration frequency agree well with calculated values.
6. CONCLUSION
Dalian Xinhai Bay Bridge is a cable net steel bridge with a single inclined tower. There are several difficulties in design and construction of the bridge. Using an analytical method, the configuration of the cable system and hanger forces of final state of the bridge are determined. A scale model is made and tested to study the mechanics and construction method. Finally, static and dynamic load experiments are performed on the completed bridge to further verify the correctness of the calculated results.