Experimental And Simulation Study Of Posttensioned Prest-ressed Concrete Beams Under Grouting Defects Based On Bond Slip Constitutive

In the corrugated pipe where the post-tensioned prestressed tendons are located,the problem of grouting defects is common.The neglect of the grouting defects brings huge safety risks to post-tensioned bonded prestressed concrete structures or components.Research and assessment of deficiencies are relatively inadequate.The existence of grouting defects makes the strands and the concrete deformation uncoordinated,which results in a reduction in the bearing capacity of the prestressed concrete members.Therefore,this paper studies the problem of grouting defects by using a combination of experiments and finite element analysis,provide a reference for the evaluation and reinforcement of prestressed bridges with grouting defects.Based on the bond between steel strands and grouting,the influence of grouting defects on the performance of prestressed members is studied in this paper.Through the pull-out test of the steel strand in the corrugated pipe,the influence of different factors and grouting defects on the bonding performance of the steel strand in the corrugated pipe was analyzed.Bond-slip constitutive model of steel stranded wire in corrugated pipe obtained by fitting experimental data,using ABAQUS finite element analysis to analyze the effect of grouting defects on the properties of prestressed concrete members.The main research contents of this article are as follows:(1)The bond-slip constitutive relationship of steel strands in a corrugated tube was established through two sets of pull-out tests.The first group of test pieces are drawn short test pieces that take into account three factors affecting the bonding performance,such as the diameter of the bellows,the bonding length,and the thickness of the protective layer.The larger the thickness of the protective layer of the steel strand and the diameter of the bellows,the characteristic bond strengths τ0 and τu of the test piece basically accord with the relationship of linear growth;The influence of the bond length and characteristic bond strength of the steel strand appears to increase first and then decrease.The second group of specimens is for long specimens with defects in grout length and grout fullness.With the increase of the defects of grout length and grout fullness,the characteristic bond strengths τ0 and τu approximately decrease linearly.The bond-slip constitutive model of the steel strand in the duct was fitted according to the test results.(2)ABAQUS finite element simulation of drawing testThe non-linear spring Spring 2 unit was used to simulate the bonding force between the steel strand and the slurry.The bond-slip constitutive relationship of the steel strand obtained in the pull-out test was converted into a change in the stiffness of the spring,simulation of the pull-out test.The analysis of the axial stress growth and distribution of steel strands was obtained.The stress at any position of the steel strand is linearly increasing with the load.The axial stress distribution of the steel strand shows a linear decrease from the drawing end.Where there is a pressure drop cavity,the stress of the steel strand is the same everywhere.(3)Finite element simulation of prestressed concrete beams with grouting defectsThrough the ABAQUS finite element simulation,the length and location of grouting defects,and fullness of grouting on the bending performance of the beam.The existence of pressure drop defects in pure bends has a greater impact on the ultimate bearing capacity of the beam;when the degree of fullness of the grouting defect is greater,the ultimate bearing capacity of the beam is lower;When the grouting is full,the stress increase of the steel strand at the beam end is small.Based on the formula for calculating the bearing capacity of unbonded prestressed concrete beams,the bond reductioncoefficient Ωu*for concrete with different degrees of grouting defects in pure bending and bending-shearing sections is set.The formula for calculating the bending capacity of prestressed beams in the presence of grouting defects is derived.