Experimental Study And Theoretical Analysis On The Flexural Behavior Of The Prestressed Composite Box Beam Structure

Prestressed composite beam is a new structural form which combine the modern prestressing technology with traditional steel-concrete composite beam.Compared with the steel-concrete composite beam, it performances better.If being chosen the steel box beam, the composite beam which has better whole performance is widely applied to the structures which bear eccentric loads.So, prestressed steel-concrete composite box beam possesses great extensive prospects in structural engineering,and it is necessary to do some research about its mechanical behavior.In order to know the mechanical behavior of the prestressed composite box beam under positive moments,ten specimens had been tested under monotonous loads.Among them,six specimens were tested with the prestressed composite beam,three specimens were tested about simulating reinforcement of conventional composite beam by external prestress technolog,one specimen was tested with the nomal composite beam. The experimental results of prestressed composite beam, including deformation, section strain,cracking distribution, failure mode, were analyzed in details.The influence of prestress degree,distribution forms of prestressed tendons and loading modes on prestressed composite beam's flexural behavior had been discussed in details.Experimental phenomena and data indicated that the prestressed composite beam had more adventages than the normal composite beams and the prestress technolog could be used to improve the flexural performance of the existing composite beam.On the base of the experiments,firstly, the prestress increment had been calculated by using different methods according to stress characteristics of the beam in different loading stages,that is ,in elastic stage,the calculation formulas of the prestress increment were derived based on the energy method and at plastic limit state,the deformation of the prestressing tendon was calculated by solving the beam's deflection and rotation.The calculation value agreed well with the experimental data.Secondly,the prestressed composite beam was analysed by elastic and plastic methods. The calculation formulas of deflection and yield load in serviceability limit state was derived considering the slip at the steel-concrete interface,and on the premise of plane section and complete composite action,the expressions of prestressed composite beam's ultimate plastic capability were deduced based on simplified plastic theory.These foumulas reflected the beam's stress characteristics ,and the calculation results met the precision requirements.Thirdly,based on the elastic-plastic theory ,the nonlinear analysis model of composite beam bending processes was established considering the nonlinear of material and geometry,also a series of the calculation formulas were derived based on the method,and the calculating program was compiled by Visual Basic (VB).The characteristic curves of the beam which calculated by the program agreed well with the test curves. At last,the influence parameters of the bending capacity of the prestressed composite beam was analysed,and the design suggestion were given.