Bond-Slip Test Between High-Strength Steel Tube And Ultra-High Performance Concrete

The bond-slip behavior between steel reinforced concrete and core concrete is a key factor affecting the quality of steel reinforced concrete and the main reason for their synergistic performance.Ultra-high performance concrete(UHPC),as a new type of cement-based composite material,has many advantages.Injecting UHPC into highstrength steel tubes can form a high-strength steel tube-UHPC composite structure,which can fully utilize the excellent properties of UHPC and high-strength steel materials and has good application prospects.However,research on the bond-slip behavior of this composite structure is limited and still in its infancy,so it is essential to study its bonding performance.This paper explores the feasibility of using a piezoelectric material-based method to monitor the bonding process of high-strength steel tube-UHPC columns based on the research on the bonding performance of highstrength steel tube-UHPC columns.The main research findings are as follows:(1)Axial monotonic loading tests were conducted on 22 high-strength steel tube ultra-high performance concrete columns to study the influence of aspect ratio,thickness ratio,steel fiber content,and curing regime on the bond-slip behavior of the specimens.The results showed that with the increase of aspect ratio,the bond failure load of the specimens gradually increased and the initial stiffness of the specimens improved to a certain extent;with the decrease of thickness ratio,the bond failure load of the specimens significantly increased and the initial stiffness of the specimens increased;with the increase of steel fiber content,the bond failure load of the specimens first increased and then decreased,and the initial stiffness of the specimens did not change significantly.The bond failure load under natural curing conditions was slightly higher than that under standard curing conditions,and there was no significant difference in the initial stiffness of the specimens under the two curing regimes.The load-slip curves of the specimens showed two forms: one had a clear peak point,and the curve rapidly decreased(with some exhibiting a tail-up phenomenon)after the peak point;the other had no obvious peak point,and the curve continued to slowly increase after the inflection point.The bonding strength of each specimen was calculated based on experimental data,and the influence trend of various parameters on bonding strength was analyzed.Longitudinal strain gauges were pasted on the outer side of the steel pipes to obtain the distribution law of longitudinal strain on the outer side of the steel pipes with the changes of height and load.The factors affecting longitudinal strain were analyzed,and the mathematical description of the strain distribution curve was determined to determine the length of the shear transfer zone.The bonding stressrelative slip curve was obtained,and a τ-s constitutive model was proposed based on this.(2)Smart aggregates were embedded inside ultra-high performance concrete,and piezoelectric ceramic patches were pasted on the outer side of the steel pipes to monitor the bonding failure process of the specimens,using the wavelet toolbox provided by MATLAB to calculate the total energy of the signal,verifying the feasibility of monitoring the bond-slip process of high-strength steel tube ultra-high-performance concrete columns based on piezoelectric materials.The experimental results show that this method is feasible and has certain advantages.(3)Using the parameters of long-to-diameter ratio,diameter-to-thickness ratio,steel content,and hoop coefficient,combined with experimental data and regression analysis,proposing a formula for calculating the bond strength of high-strength steel tube ultra-high-performance concrete columns.The calculation results were compared with the experimental results,and the agreement between the calculation results and the experimental results was good.