方钢管超高性能混凝土界面黏结滑移性能

：为研究方钢管超高性能混凝土（UHPC）的界面黏结滑移性能，以钢管宽厚比、高宽比和UHPC强度为主要参数，设计了18个方钢管UHPC试件并对其进行静力推出试验.通过试验分析了试件的破坏过程与形态、荷载-滑移曲线、黏结强度和钢管纵向应变分布，结果表明：推出后的试件整体较为完整，钢管无鼓曲现象，加载端边缘处混凝土有一定损伤；加载端与自由端的荷载-滑移曲线形状基本一致，且曲线分为有明显峰值点的弱化型和无明显峰值点的强化型两类；黏结强度随宽厚比和高宽比的增加而减小，当宽厚比较大时，增大UHPC强度可以明显提高黏结强度；加载端的钢管纵向应变小于自由端，应变沿高度方向大致呈指数分布.从黏结强度的组成出发，忽略化学胶着力影响，通过确定界面摩擦和机械咬合应力的表达式，建立了方钢管UHPC在两种养护条件下的黏结强度计算模型，理论计算与试验数据符合较好.

Study on Interface Bond-slip Behavior of Ultra-high Performance Concrete-filled Square Steel Tube

In order to study the interface mechanical behavior of ultra-high performance concrete (UHPC) filled square steel tube, 18 UHPC-filled steel tube specimens were designed for static push-out test, and the width-to-thickness ratio, height-to-width ratio, and the compressive strength of UHPC were considered as main parameters. The failure process and patterns, load-slip curves and bond strength of specimens, and the longitudinal strain of steel tubes were analyzed. The results show that the specimens are intact after the test and there is no visible local buckling on steel tubes, while some damage is formed around the edge concrete at the loading end. The load-slip curves are essentially the same at the loaded and free ends, and the curves are divided into two categories: weakened with a clear peak point and strengthened without a clear peak point. The bond strength decreases with the increase of the width-to-thickness ratio and height-to-width ratio. When the width-to-thickness ratios are large, increasing the strength of UHPC can significantly improve the bond strength. The longitudinal strain at the loading end of the steel tube is slightly larger than the value at the free end, which exhibits a negative exponent distribution along the height. Based on the composition of bond strength, the expressions of interface friction stress and mechanical interaction stress are determined by ignoring chemical adhesive force. The calculation model of bond strength for UHPC-filled square steel tube specimens under two curing conditions are respectively proposed, and the theoretical results agree well with the experimental data.