Study On Key Technology Of Construction Control For Single Tower Hybrid Cable-stayed Bridge

Single tower hybrid cable-stayed bridge is composed of concrete and steel.The concrete part of the side-span have more deadweight and improve the overall stiffness of the structure.The steel beam can reduce the weigh of the main beam to improve the span capacity.Because the material properties of concrete and steel can fully play,single tower hybrid cable-stayed bridge have good economical efficiency and have been widely developed and used in the bridge construction at home and abroad.Construction control plays an important role in the process of bridge construction,which is the key to ensure the shape and stress condition of the bridge meet the design requirements.Based on the background of Tanjiang Bridge,this dissertation studies the finite element modeling calculation in the early stage and the key technical problem in the process of construction control.(1)Firstly,the dissertation introduces the development and characteristics of the single tower hybrid cable-stayed bridge.Based on the understanding of several common methods for constrstion control of cable-stayed bridges,and combined with the structural characteristics and construction methods of Tanjiang Bridge,the double objective geometric control method is used to control the bridge construction.(2)The building process of finite element model for Tanjiang Bridge is introduced in detail.There are three common mechanical models of cable-stayed bridge and the double-beam model is used.The spatial beam element is used to simulate the tower and beam.In addition,the plate element is used to simulate the bridge deck and the cable element is used to simulate the cable of the bridge.The principle of the division of element is discussed.(3)Different from tower-beam asynchronous construction,the method of tower-beam synchronous construction has the advantage of shortening the construction period.Comparing the bridge response of two construction methods,it can be seen that the deformation and cable force of bridge are different.By studying the parameter sensitivity of bridge under the synchronous construction,we can know that the tower stiffness,the weight of beam and the cable force are the main parameters influencing the tower.A reasonable pre-displacement and pre-lift should be set when controlling the tower shape.Besides,it is necessary to precisely calculate position of cable duct,especially the angle of cable duct.(4)When the cable duct is precisely positioned,the modified calculation of sag and pre-camber about cable duct’s angle is necessary to be done to ensure that the cable is located at the center axis of cable duct at the stage of bridge completion for the purpose of convenient installation of shock absorber.By calculating the allowable angle deviation of cable in the duct,we can judge whether the cable and duct are in conflict with each other when the cable is tensioned.In addition,the regular pattern of cable duct’s variation at the whole process of constrution of bridge is also studied.(4)The cable of Tanjiang Bridge adopts the second stretching method.Construction cable force is calculated reasonable when initial stretching force can ensure stress-free closure of steel beam and secondary stretching force can make the final cable force of the bridge meet the design requirements.When it comes to the calculation of stress-free cable length,the difference of results between parabola theory and catenary theory are very small.Calculating the pull-out length of cable and checking the anchor length to ensure that nuts on the anchor are in effective zone during the stretching process of cable.(5)The vibration frequency of cable can be calculated quickly and accurately based on the dynamic finite element theory,especially the high order frequency.By studying the parameter sensitivity of cable frequency,the influence of bending stiffness,boundary condition and cable force on frequency is obtained.