Investigation Of The Influences Of Grouting Defects And Anchorage Failure On The Mechanical Performance Of Post-tensioned Concrete Beams

The development of prestressed concrete structures allows the construction of longer span bridges with reduced material and higher durability.Grouting is one of the most important phases in the construction of post-tensioned concrete beams.However,grouting defects have been reported in numbers of existing bridges in late decades.The existence of grouting defects changes the overall behaviour of prestressed members,eases corrosion,and even causes the fracture of the prestressing tendons.In the event of end anchorage system failure,the prestressing tendons were assumed to fail completely and no longer contributed to the bearing capacity of the structure.Additional reinforcement measures were then needed to ensure that the bearing capacity of the structure met the requirements,resulting in higher cost of structural rehabilitation or demolition.Based on this,the degree of grouting defects is taken as parameter,and the influence of anchorage system failure on the flexural performance of prestressed concrete beams is investigated through experimental,numerical,and theoretical analysis.The main research contents and conclusions are as follows:(1)Seven simply-supported post-tensioned prestressed concrete beams specimens were constructed,and the influences of end anchorage failure and grouting defects on the flexural performance of the beams were analysed.The secondary anchorage induced after the failure of the end anchorage system was studied and the change of failure mode of the test specimen with the grouting condition was determined.Moreover,the effects of grouting defect location on the prestress camber,stiffness,ductility,and crack resistance were quantified.The results showed the location of the defects has no detrimental effect on the elastic behaviour,but highly affects the crack resistance of the prestressed concrete beams.(2)Through numerical analysis method,detailed models considering the bond at the interface of the prestressing tendons and grout,and the material nonlinearity were established.The influences of the length and location of grouting defects on the bearing capacity,stiffness,crack resistance and ductility of prestressed concrete beams were further discussed.Additionally,the secondary transfer length induced in the structure after the failure of the anchorage system was investigated and the influence of grouting defects on residual prestress was addressed.The results showed that,there is a linear correlation between the length of grouting defects and the ultimate bearing capacity,and the failure mode of the beams is dependent of the length of grouting defects,while the ductility of the specimens increases with the increase of the length of the grouting defect.Prestressed concrete beams with grouting defect in the end region show shorter secondary prestressed transfer length.(3)A nonlinear analysis method for partially grouted or fully grouted beams with grouting defects subjected to the action of two-point flexural load is proposed.The analysis method is based on the experimental and numerical analysis results,the overall strain compatibility theory,the curvature approach,and section analysis at critical sections.Finally,a method of analysis of partially grouted beams or fully grouted beams with grouting defects subjected to uniform load action is proposed based on the principle of equivalent load.134 Pictures,26 Tables,152 References。...