Researches On Stability And Wind Effects Of Rigid Frame Bridges With Flexible Twin Piers During Cantilever Erection

Balanced cantilever erection for continuous girder bridges, continuous rigid frame bridges(CRFB) and cable-stayed bridges has been recognized as one of the most efficient methods of building bridges without the needs for falsework. Because of its economy and convenience for construction, the CRFB with high flexible twin piers(HFTP) are commonly built in China. While several problems exist in cantilever construction stage, this paper focus the studies mainly on stability and wind effects.1) The critical loads of single-floor, multi-floor rigid frame were deduced, and simplified formula of stability coefficient relative to the HFTP with two horizontal connecters during cantilever erection were also obtained. This simple formula is of convenient, and can be used to analysis the stability of different cantilever construction stage of the XiaoGuan Bridge, the efficiency and validity were confirmed after comparing the results to that of from FEM.2) The moving equation of the structural model, which was simplified from the balanced cantilever structure of the CRFB with the HFTP, was deduced by using the Lagrange Equation. Accordingly, the free vibration frequency could be obtained. This method was employed to obtain the dynamic characteristic of the XiaoGuan Bridge. It was found that the results of the presented method were in better consistence to that of from FEM and field tests. This simple and fast algorithm could be used without help of FEM program, which is suitable for bridge construction.3) Ambient vibration tests were carried out on 3^nd pier of the XiaoGuan Bridge during the balanced cantilever erection, the results from the field mode tests were compared with that of FEM and that of the present algorithm, good agreements were found. So, a new fast approach connecting the construction stability, model updating technology and field mode test was presented to duly evaluate the structure stability.4) The CFD method was applied to study the Wind loads on HFTP of CRFB, both in longitudinal and lateral directions. The effects on aerodynamic drag coefficient subject to change of geometrical parameters in HFTP were studied. Based on aerodynamic coefficients from CFD, the galloping stability of the XiaoGuan Bridge during the maximum cantilever stage was also studied.5) A wind load model of CRFB with HFTP at erection stages was employed taking into account all wind effects on girder and piers. The influence function was presented which could be attained by the FEM. The wind effects on inner forces at bottom of piers were decomposed into different parts that could be acquired from different way. The peak maximum was obtained by using the gust factor to set up the relation between the buffeting effect and the peak maximum. Finally, the application was illustrated with reference to the XiaoGuan Bridge. It was shown that taking all the roles of different loading components into consideration is very important.