The Flexural Properties Of Unbonded Prestressed Concrete Beams With Corroded Steel In Compression Zone

The corrosion of reinforcement in concrete member, not only causes the loss of strength of steel bars and the reduction of cross section area, but also produces the rust which the volume of these corroded products expand to create radical pressure to the surrounded concrete of reinforcement, namely bulging force. Because of bulging force, the surrounded concrete produces the circumferential tension stress which renders the concrete of compressive region under the condition of biaxial tension-compression; cracks could appear so that reduces the loading ability. The present paper conducts a simulation analysis on what effect of the rust steel bars of compressive region has on the flexural performance of unbonded prestressed beam by using large-scale finite element software. The primary work as followed:This study summarize the research of concrete durability.Exploring the method of finite element analysis of steel corrosion in unbonded prestressed concrete beam, determining the constitutive relation of the material and the structural unit model, analysing the failure criterion of concrete cracking,the softening and cracking, cracks and crushing processing.Analysing what the corrosion of compression rebar affect the unbonded prestressed beams’bending performance by different corrosion rate of unbonded prestressed concrete cantilever beams through numerical simulation in different prestress,load,the diameter of compression rebar and concrete strength. Then analyse the result of simulation and experiment from the unbonded prestressed cantilever beams and prestressed steel corrosion and strain’s changes of concrete in compressive zone.In the condition of the reasonable premise of the basic assumption, deduce the rust expansion degradation calculation formula of the normal section flexural bearing capacity of unbonded prestressed concrete beam before its compressive zone start to craze for the rebar corrosion. By the study for finite element simulation to normal section flexural bearing capacity at different corrosion rate before unbonded prestressed concrete beam’s compressive zone start to craze for the rebar corrosion, compare the simulation result with the formula result, and analyse the influence of the factor of thecomprehensive reinforcement index to the bearing capacity.This study obtained the following results:After the compressive zone of unbonded prestressed concrete beam being rusted, its bending performance will reduce with the increase of the amount of the rust.With other conditions being equal, when prestress, external load and bar diameter increase or concrete strength grade decrease, the amount of the rust during longitudinal cracking of compressive zone of concrete will be smaller and the relative deflection increment will be reduced either. The present paper deduces the formula for calculating the degenerated normal section strength under the condition of bulging force while the corroded steel bars of unbonded prestressed concrete in compressive region isn’t break. From the simulation analysis on the global reinforcement index such as the size of the effective prestressing、the amount of prestress reinforcement and the number of tensile steel bars. Good agreement is shown between the simulation and the formula deduced by the present paper, and it is of instructive significance for preliminary assessment of durability in the future.