预应力UHPC/RC阶梯桩-土相互作用的拟静力试验研究及数值分析

整体式无缝桥中的混凝土基桩侧向刚度过大，难以满足桥梁的纵向变形，提出一种UHPC/RC材料串联形成的阶梯桩来满足整体桥纵向变形需求。设计制作了2根UHPC/RC阶梯桩模型（无、有预应力），并对其进行水平低周往复荷载试验，通过桩身破坏特点、滞回曲线、骨架曲线、等效黏滞阻尼比、刚度退化等研究其耗能能力及抗震性能。结果表明：无预应力阶梯桩的破坏位置在3倍桩径的埋深位置，桩身开裂时桩顶的位移荷载为8~10 mm；有预应力阶梯桩的破坏位置在6倍桩径的埋深位置，桩身开裂时桩顶的位移荷载为10~15 mm。说明预应力的施加能有效提高阶梯桩抗裂能力及抗震性能，并满足整体桥水平变形需求。采用OpenSees软件对阶梯桩支承的整体桥进行参数分析发现，预应力度、桩上下段长度比与刚度比增大均可提高阶梯桩的水平承载力与变形能力。

Pseudo-static test and numerical analysis of prestressed UHPC/RC segmental pile-soil interaction

The reinforced concrete piles (RC) in integral abutment bridges (IAB) are challenging to meet the longitudinal deformation of bridges with significant lateral stiffness. This paper proposes a new form of pile comprised of UHPC and RC piles in series to meet the longitudinal deformation demand of IAB. Tests were conducted for two UHPC/RC segmental piles (with or without prestressing). The failure characteristics, hysteretic behavior curves, skeleton curves, equivalent viscous damping ratio, and rigidity degeneration were developed using horizontal displacement loads. The failure position of the non-prestressed segmental piles is at the buried depth of three times the diameter of the pile, the displacement of the pile top when the pile cracks is 8-10 mm; the failure position of the prestressed segmental piles is at the buried depth of four times the diameter of the pile, The displacement of the pile top when the pile cracks is 10-15 mm. The results show that prestressing can effectively improve the resistance cracking capacity of step piles and seismic properties, while meeting the deformation requirements of IAB. The finite element model (OpenSees) was used for modeling and analysis. The analysis results show that the horizontal bearing capacity and deformation capacity of stepped pile can be improved by the increase of prestress degree, the ratio of length and stiffness of pile.