Tension Experiment Analysis And Finite Element Study Of Retard-bonded Prestressing Steel Strands

The technology of retard-bonded prestressing（RBP）has the advantages of simple and easy construction of the unbonded prestressing technology and the mechanical characteristics of the effective bonding of the bonded prestressing technology,and at the same time overcomes the technical disadvantages of both,so it has received the attention of engineering and academic circles.The current《Technical specification for concrete structures prestressed with retard-bonded tendons》calculates the prestress loss valueσ_l2 caused by the friction between the ribbed retard-bonded prestressing steel strand（RPSR）and the sheath wall without considering the effect of viscous force;The effect of viscous force is not considered when calculating the theoretical extension value of RPSR tension;the calculation formula of prestress loss caused by batch tension of RPSR is not proposed.Research on the mechanical properties of RPSR and the finite element model of retard-bonded prestressed concrete beams is not sufficient.The main contents of this article are as follows:（1）Study on the viscous force between RPSR and sheathThrough the actual measurement of the strain of RPSR under the tension of three27-meter-span RBP beams in the actual project,the calculation and correction are transformed into the RPSR normal stress;Analyze the changes of RPSR stress and its prestress loss under the action of tension force at various levels.The first batch of prestress loss during RPSR tensioning is calculated,and the prestress loss valueσ_l2caused by the friction between the RPSR and the sheath wall is obtained by the segmented calculation method.After deducting the frictional prestress loss,the RPSR stress is compared with the normal stress of the RPSR under the measured holding state,and the viscous force between the RPSR and the sheath at the experiment temperature is obtained.The actual tensile length of RPSR and the tensile time of RPSR are measured through experiments to verify the calculated viscous force.The segmented calculation method is used to theoretically calculate the tensile and tensile length of the curved RPSR,and the calculation formula for the theoretical tensile and tensile length of the RPSR after considering the viscous force is deduced.（2）Research on the loss of prestress caused by batch tension of RPSRTwo methods are proposed for calculating the loss of prestress in batches.The equivalent balance analysis method regards the concrete section as a whole,and the force of RPSR on the concrete section is evenly distributed to the entire concrete section;The section stress analysis method regards the concrete at the center of gravity of the RPSR as an independent entity,and calculates the stress generated by the post-tensioning RPSR on the concrete at the center of the first-tension tension.Comparing and analyzing the two methods,it is concluded that the equivalent balance analysis method is simple in calculation,but not accurate enough;The section stress analysis method can fully consider the mutual influence of RPSR at different positions and different positions in the concrete section,which is more realistic,but the calculation amount is large.（3）Finite element simulation study of RPSR batch tensionThe finite element model of the tension stage of RPSR is established by adopting the methods of local coordinate coupling,MPC constraint and node cooling,and through theoretical calculation of the stress on the RBP concrete beam and arching in the middle of the span,the feasibility of the finite element model of the RBP concrete beam in the tension stage is verified.On this basis,it is proposed that the boundary conditions of RPSR are used to constrain the displacement in the length direction,the method to simulate and study the mechanical performance of the retard-bonded prestressed concrete beam after the setting retarder is cured.The article has 69 pictures,57 tables and 97 references.