Axial Vibration Analysis Of Vertical Prestressed Steel Bar

The prestressed concrete box girder bridge has many advantages such as nice structural integrity,strong bending rigidity,better torsional performance,reasonable mechanical performance,less expansion device and so on.Setting vertical prestressed finish rolling rebar in design stage is an important measure to prevent the web cracking.Most of bridges are cannot without the vertical prestressed finish rolling rebar.But there are still some oblique cracks in the web during the operation.The vertical prestress lose efficacy is one of main casue of the web cracking.At present,the exposed section of vertical prestressed finish rolling rebar is the effective tensile force test method of the cantilever beam model.During the application process,it is found that the construction unit does not match the screw thread tolerance of the purchased nut and the finish rolling thread steel bar.The stiffness of the exposed section with the same tensile force is different,lead to the measurement of effective tensile force error.On the other hand,the cantilever beam model of the nut anchorage section and the finish thread steel bar are regarded as the completely fixed cantilever beam model,and the error occurs when the tensile force is lacked.This paper is based on the method about the cantilever beam model,the axial vibration of finish rolling rebar and the test principle about the effective tensile force of finish rolling thread steel bar is studied.The main research contents of this paper as follows:This paper is based on the theory of threaded connection of anchor nut and anchor plate and finish rolling thread steel bar.According to the thread connection,a discrete mechanical a model of steel bar used to analyse axial vibration is established.A model of the motion equation is obtained according to Darren Bell principle,and the formula of model parameter is deduced.Base on the free vibration with the finish rolling thread steel bar,the characteristic equation of two unknown parameters including in the contact stiffness of anchor nut and the anchor plate and the natural frequency of the model are obtained.Put forward the inherent frequency of the anchoring system of vertical finishing rebar,the contact stiffness between anchor nut and anchor plate is obtained by the characteristic equation,and the relationship between the contact stiffness and the normal force of contact surface is monotonically proportional to the contact force.The feasibility of the discrete model of the axial vibration ofthe rebar system in the finish rolling rebar is verified by the indoor test and the field bridge test,and the contact stiffness and natural frequency are proportional to the tensile force,and the contact stiffness has a good linear relationship with the tensile force.The work of this paper provides theoretical and experimental basis for the development of vertical prestressed testing instrument,and has important application significance.