Research Of Bending Performance Of External Prestressed Simply Supported Concrete Beam Under Bearing Capacity Limit State

The biggest characteristic of externally prestressed concrete structure is the prestressed tendon layout on the outside of the girder, the prestressed tendon be connected to structure only on the anchor end or steering blocks. Compared with internal prestressed concrete structures, externally prestressed concrete structure can simplify the process of tensioning, decrease the friction loss, easy to casting, and easy to replacing or check prestressed tendons and so on. Although it has been widely used in engineering practice, its theoretical study is not yet perfect.on the foundation of existing research achievement, In this paper we studied the mechanical property of externally prestressed concrete simply supported beam under ultimate limit state, the main work is as follows:1、Have analysised and summarized the mechanical property of the externally prestressed concrete beam and the factors that affecting its mechanical performance while the structure reached to bearing capacity limit state.2、analysed the different and point out the respective advantages and disadvantages between externally prestressed concrete structures and internally bonded or unbonded prestressed concrete structures and cable-stayed structure.3、Under the condition of considering material nonlinearity and geometrical nonlinearity, using analysis software ansys did a whole process finite element simulation and analysis of externally prestressed concrete beam, By comparing the value of calculation and experimental, verified the feasibility of using finite element program to analysis the mechanical properties of externally prestressed beam, the calculated data can be used as supplement of test data.4、according to the concrete plastic hinge theory, study the relationship of deformation that between the overall beam and externally prestressed tendons,under the two hypothesis of respectively assume the deformation shape of beam is line and arc while in ultimate limit state. This paper have deduced the stress calculation formula and put forwarded the corresponding solving method of five kinds arrangement of externally prestressed tendons of externally prestressed concrete beams.this five kinds is:straight bar arrangement beam without deviator、straight bar arrangement beam with one deviator、straight bar arrangement beam with two deviator、curve bar arrangement beam with one deviator and curve bar arrangement beam with two deviator (Respectively, in following text we named this two method as line method and curve method for short). And then, use these the two methods calculated five different kind of externally prestressed concrete test beams, And compared the calculated value with the test results in order to study the applicability of this two method.5、in this paper established the bending strength calculation formula for externally prestressed concrete beam under ultimat limit condition, and in this formula we have taken secondary effects into consideration. Under the precondition of consider or not consider the second-order effect, use the line and arc method whitch established in this paper calculated the same test beam named pb-1 respectively. So we can precisely analyze the effect of second-order on ultimate bearing capacity of externally prestressed concrete beams.