Analysis Of The Influence Of Grouting State On Post Tensioned Beam Structure Based On The Bond Property Of Prestressed Steel Strand

Grouting defects widely exist in post-tensioned bonded prestressed systems in our country and even in the world and are seriously harmful,bringing huge potential safety hazards for transportation.Bond performance between corrugated steel strand and cement paste is often neglected in post-tensioned prestressed structures.In fact,good bond can increase the Compatibility(mechanics)of steel strand and cement paste,and the lack of bond will affect the bearing capacity and ductility of the structure.In this paper,from the perspective of bonding,the influence of grouting defects on the prestressed system is analyzed,30 short-drawn specimens and 21 long-drawn specimens are made,and the influencing factors of bonding performance are analyzed through steel strand pull-out test and the corresponding bonding slip curve is fitted.The bond-slip constitutive relation model obtained from the test is substituted into the ADINA finite element analysis model as a parameter to analyze the influence of bond defects on the mechanical properties of the simulated beam.The main research results are as follows:(1)According to the test results of short pull-out specimens,the influences of protective layer thickness,bellows radius and bonding length on the bonding performance of steel strand in bellows in back tension beam are analyzed,and the corresponding test parameters are fitted to establish the bond-slip constitutive relation model of steel strand and slurry in bellows.The test results show that in a certain range,the larger the relative protective layer thickness,the larger the bellows radius ratio,and the shorter the relative bonding length,the better the bonding strength of steel strand.(2)According to the pull-out test results of long specimens,the influence of grouting defects on the bonding properties of steel strands is analyzed,and the test results show that if the defect section is long and the defect percentage is large,the bonding properties of steel strands will deteriorate and the influence of defects on the bonding properties will become significant.Two defect factors,length ratio of defect section and grouting plumpness,are taken as relevant parameters to establish a corresponding bond-slip model.The theoretical model is in good agreement with the experimental results.(3)Using finite element analysis software,taking the degree of grouting defects as a variable,the stress performance weakening effect of post-tensioned beams with different degrees of grouting defects is analyzed.The analysis results show that there is little difference between the defective beam and the intact beam at the initial stress stage.After the beam cracks,the longer the length of the grouting defective section and the larger the percentage of defects in the section,the more obvious the decrease in the ultimate bearing capacity and ductility coefficient of the beam.