Research Of Mechanics Character On Joint Parts Of Hibrid Girder Cable-stayed Bridge

The hybrid girder cable-stayed bridge has exhibited great vitality owing to its unique technical features since the concept of the kind of the bridge was first developed in1960s. In the process of about40years’ development, more than20bridges of such kind have been successively built in China and other parts of the world. Particularly in the recent10years, rapid advances having been made for the bridge in aspect of its construction numbers, construction scale and span length increase strike attention of bridge engineers. However, it is unfortunate that lack of systematic analysis and study of the key technique, the joint parts of the bridge has remained unimproved up to this date.In this paper, against the background of Taoyaomen Bridge in Zhoushan, a hybrid girder cable-stayed bridge project, the author conducts a systematic and deep-going study of several important issues of mechanical conditions, force transmission ways, rigidity matching and reliability of the joint parts of the hybrid girder cable-stayed bridge, respectively using methods of finite element analysis, model tests, construction control and filed measurement of the mechanical conditions of the bridge at operation stage.The author in the first step briefly reviews the development process of the hybrid girder cable-stayed bridge, analyzes the structural features and application range of the bridge and systematically summarizes the structural forms, features, determination of locations and mechanism of force transmission of the joint parts of the bridge, and at the same time, also presents some new ways to form the joint parts between the steel and concrete girder structures of the bridge.With the finite element analysis method, the author makes simulation calculation for joint parts of actual bridge, analyzes influences of rigidity matching of the main girders at the joint parts made up of two kinds of materials on the global force transmission of the parts. A model for the joint parts of the actual bridge is created first, further to the model, another five models are then set up by changing concrete filling amount and dimensions of stiffening ribs of the steel girder. Through comparison and analysis of the calculation results of all the six models subjected to the same load cases, the form of best rigidity matching for the joint parts is obtained. Finally, the safety coefficients of the optimized joint parts under1.7times of the most unfavorable load combination are verified, and the stress distribution and cracking resistance capacity in the adjacent areas of the joint parts are analyzed as well. The shear studs arranged in the joint parts of the hybrid girder cable-stayed bridge play vital role in joining the girders of two kinds of different materials. By means of finite element method and with reference to the layout of shear studs in large scale segment model tests, the author analyzes the mechanism of mechanical conditions, force transmission and distribution laws of the shear studs. Through comparison and analysis of three kinds of mechanical conditions of the shear studs, it is believed that the contact analysis is closest to the actual conditions and the forces in such analysis are reasonable, and further the author analyzes the longitudinal and lateral distribution of shear stud forces and also slip between the interfaces (bottom plates, top plates and webs) of the steel and concrete structures in terms of1.7times of the most unfavorable load combination. The laws obtained therefrom may serve as reference to the similar design. To have a better understanding of the mechanical conditions of the shear studs, nine specimens for single stud push-off test are purposedly made and the relationship between load and shear force of the single shear stud push-off test is obtained after test.The model test can demonstrate in a clear and direct way the whole process of a structure from being loaded to failure. In this case, the test is one of the important means of verifying structural design and of studying mechanical conditions of the structure. In this paper, in the light of the specific conditions of Taoyaomen Bridge, the theory of similarity is used to make a study of large scale segment model tests. In the tests, the load is applied respectively in terms of0.5,0.7,1.0,1.2,1.4and1.7times of the designed load combinations. The strain values at various measurement points of the measured sections of the joint parts under different designed load combinations are analyzed with particular efforts made for the analysis of the mechanical conditions under1.7times of the most unfavorable load combination. Through analysis of the test results, the author obtains valuable measurements of sectional positive stress distribution, cracking behavior and shear lag effect, and forces of U ribs, longitudinal transmission of stress and shear stress distribution laws under different load cases.On the basis of brief summarization of construction control methods for cable-stayed bridges, and in the light of the structural features of the hybrid girder cable-stayed bridge, the author puts forward a construction control method of least differential control by classification. With the method, the closure of Taoyaomen Bridge was completed smoothly and in high precision, and two years after completion, oft the; Bridge, the stay cable forces of the Bridge were again inspected and tested in order to have an understanding of time-dependent variations of the cable forces of the Bridge. The method and test in question are of referential significance to guiding the design and long-term observation of cable forces of cable-stayed bridges.The test study of mechanical conditions of a bridge at operation stage is one of the effective means of checking up construction quality of the bridge. At the operation stage, the author mainly carries out a study of stress, strain variation laws and dynamic behavior of the joint parts of the hybrid girder cable-stayed bridge. The results of test study reveal that the joint parts of the bridge at operation stage have considerable safety reliability and can ensure normal operation of the bridge.