Research On The Design Method Of Cable Unseating Prevention Device

According to the phenomenon of bridge falling caused by earthquake,foreign countries,especially the United States and Japan have conducted study on collapse-proof systems systematically and applied it to practical engineering widely,and the design method of collapse-proof systems is specified in bridge codes.The research of the collapse-proof systems is in the just beginning stages and the design rules also are drew from Japanese experience.The cable unseating prevention device is an important part of collapse-proof systems and is the ultimate safety measure to prevent the falling beam.In the earthquake,the interaction between bridge and unseating prevention device is a dynamic process and prevention failing effect can be affected by many factors.The Japanese static design method of unseating prevention device is still adopted in China,not considering device actual force under the earthquake,and its effect is not good.Under strong earthquake,the device itself may be destroyed.In addition,the domestic bridge form,seismic design ideas and the structural form of unseating prevention device are different from Japanese,so the applicability of Japanese design methods in China has not yet to be confirmed.Therefore,the dynamic research on the unseating prevention device can be conducive to form the design method of unseating prevention device which correspond to domestic bridge seismic design.It is of great significance for the future construction of bridge engineering and earthquake disaster prevention work.The main research work are done in this paper as follows:(1)This paper introduces the composition of the collapse-proof systems,analyzes the development process of the domestic and foreign unseating prevention device,and analyzes and summarize the advantages and disadvantages of the different types of unseating prevention device.(2)The dynamic time-history analysis has carried on a bridge with the installation of unseating prevention device to study the response of design parameters to bridge and discuss the optimal design parameters of the device under different peak acceleration.(3)The paper analyzes the influence of the combination of different connections on the dynamic response of bridge structure and the the influence of adjacent span difference on the effect of unseating prevention device.(4)The characteristics of three design methods unseating prevention device are compared and analyzed by the example calculation and the safety of 1.5 times of constant force design method is verified.Through the above several aspects,the following conclusions are mainly got:(1)The stiffness and the design moving value of unseating prevention device have great influence on the response of the bridge.When the stiffness of unseating prevention device which use the pier-girder mode is between 0.1-1 times of the stiffness of pier,the effect of device is better;the greater the peak acceleration,The greater the upper limit of the design moving value of the device work.(2)By changing the side span,this paper can get the law of the effect of unseating prevention device with the cycle ratio change;it is better to use the pier-girder connection than the girder-girder connection at the pier to limit the relative displacement of thepier-girder;and compared with the unseating prevention device installed at the abutment and pier,the displacement reduction of the pier-girder or the girder-girder is larger.(3)Compared with 1.5 times of constant force design method,velocity-based design of unseating device requires a cross-sectional area about 3.4 times of 1.5 times of constant force design method;And when unseating prevention device is designed by the maximum control displacement of the device,the number of strands is less than 1.5 times of constant force design method.