Study On The Stress Of Prestressed Steel Bar Of PC Beam Based On Deflection

In recent years,the technology of prestressed concrete has seen a rapid development which provides theoretical and technical support for the construction of concrete beam bridge.China has already built a large number of prestressed concrete bridges.Since the low design standard at early stage,inadequate maintenance and overload phenomenon caused by lack of effective management,varying degrees of cracking and other common diseases appear in the beam during actual operations.Due to the influence of crack,there are significant differences between design and actual structure on the mechanical properties of prestressed concrete,which bring adverse effects on safety functions of an in-service bridge.After cracking,the overall stiffness is reduced so that the beam gets into nonlinear state due to the presence of cracks.The existing nonlinear theory model are monotonic loading model while actual load conditions of beam are reiterative.In this paper,the nonlinearity of beam under cyclic load is found to be different from monotonic load through the experiment method.Therefore,the existing non-linear theory can not well calculate beam nonlinearity under cyclic load.Nonlinear study maily focuses on stiffness degradation,cracks,prestress loss,residual bearing capacity after existing prestressed concrete bridge cracking.The stress of prestressed steel which is the main force member in prestressed concrete beams is of great significance for the safety assessment of the bridge,and for the study is very lacking.In this paper,the relationship between stress and load on prestressed steel is investigated after prestressed concrete bridge cracking,which is based on test data of 3 static beams.Meanwhile,analysis of the test beam loading are carried out through an finite element software ANSYS.The calculated data of mid-span deflection and prestress is compared with the data from monotonic loading,winch shows the consistency of nonlinear calculation results and experimental data under monotonic loading.The crack width of prestressed concrete beam under different levels of load is collected to analyze the difference between the cracks.A stiffness reduction model of prestressed concrete beam after cracking is obtained,which lay a foundation for analyzing the stress of prestressed steel;Considering prestressed reinforcement stress coefficient,a reduction model based on the statistical distribution of cracks is calculated.Then,a formula for prestressed reinforcement stress increment based on mid-span deflection is obtained.The formula is verified through experimental prestressed reinforced beams stress increment data.Finally,a mid-span prestressed reinforcement stress formula based on damage stiffness analysis method for prestressed concrete simply supported beam is obtained,which provides important mentality and theoretical support for the safety assessment of prestressed concrete bridge with cracking damage.