In regions of high seismicity, the large seismic design forces sustained by the superstructure must be transferred to the bridge foundations. In these situations, in particular in situations with weak soils, cased shafts, which are concrete filled steel tube (CSFT) components, are used for piles and drilled shafts. Prior research shows that these components have large flexural, axial and shear strengths. Typically, the forces are transferred from the column to the pile through a pile cap. However, direct connections are becoming more common, in particular because they have efficiency in terms of placement and can facilitate accelerated bridge construction. This research studies two different connections: (1) direct embedment of the column reinforcement into the pile and (2) an enhanced connection using a ring at the top of the tube in the pile to enhance mechancial bond and reduce embedment depth. The study was conducted using a high-resolution finite element analysis modeling approach validated using large-scale test results of reinforced concrete (RC) and CFST components and connections. The model included advanced constitutive modeling of the concrete as well as modeling of the bond between the steel tube and concrete fill and the reinforcing steel and the concrete fill. The transfer of forces from the yielding reinforcing bars in the RC pier to the concrete fill and tube of the pile is critical for this connection. Different approaches were investigated to achieve transfer without loss of strength or ductility. A supplemental rib inside the tube ultimately was used to enhance the load transfer with the minimum embedment length. The model was used to conduct a parametric study with the following study parameters: the rib location (l_R), tube diameter (D), reinforcing bar diameter, and embedment depth (l_d). The results were used to propose initial design recommendations.

在地震多发地区，上部结构承受的大地震设计力必须转移到桥梁基础上。在这些情况下，特别是在土壤薄弱的情况下，套管轴，即混凝土填充钢管 (CSFT) 组件，用于桩和钻孔轴。先前的研究表明，这些组件具有较大的弯曲、轴向和剪切强度。通常，力通过桩帽从柱传递到桩。然而，直接连接正变得越来越普遍，特别是因为它们在布置方面具有效率并且可以促进桥梁建设的加速。这项研究研究了两种不同的联系：(1) 将柱钢筋直接嵌入桩中； (2) 使用桩中管顶部的环加强连接，以增强机械结合并减少嵌入深度。该研究是使用高分辨率有限元分析建模方法进行的，该方法使用钢筋混凝土 (RC) 和 CFST 组件和连接的大规模测试结果进行验证。该模型包括混凝土的高级本构建模以及钢管和混凝土填充物以及钢筋和混凝土填充物之间的结合建模。力从钢筋混凝土桥墩中的屈服钢筋传递到桩的混凝土填充物和管子对于这种连接至关重要。研究了不同的方法以在不损失强度或延展性的情况下实现转移。管内的辅助肋最终用于以最小的嵌入长度增强载荷传递。该模型用于进行具有以下研究参数的参数化研究：肋骨位置（l _R )、管径 ( D )、钢筋直径和埋置深度 ( l _d )。结果用于提出初步设计建议。