Research on the Brittle Fracture of Steel Profiles in Steel-Concrete-Composite Construction Systems

钢廓线包覆钢筋混凝土施工方法（在日本被称为SRC）被认为是最具延展性的方法之一，因此也是最有效的抗震结构之一。然而，在某些情况下，在这种结构中，梁与柱节点的塑性变形能力会变得很低，因为在梁端存在扇贝用于焊接，特别是在交替重复循环弯曲的情况下。为了明确钢-混凝土组合结构中，特别是钢廓线包覆钢筋混凝土结构中，梁与柱节点存在延性。交替重复循环弯曲低周疲劳断裂试验采用如图1所示的加载系统，在不同类型的节点上进行不同的恒定挠度，即图2所示的柱与梁节点（C-Butt）、梁与柱节点（B-Butt）和梁与柱节点（B-Butt- sc）。与钢筋混凝土（RC）、钢结构（S-B-Butt-Sc）和复合结构（Comp-B-Butt-Sc）等其他节点相比，钢轮廓包覆钢筋混凝土结构中这类不同类型的梁柱节点的低周疲劳断裂极限总结如图3所示。该图非常清楚地表明，由于焊接接头中扇贝的存在而缺乏延展性。封装钢构件的脆性断裂模式如图4所示。

The steel profile encased reinforced concrete construction method (named SRC in Japan) has been believed to be one of the most ductile and consequently one of the most effective construction against earthquake excitation. However, in some cases, at the beam to column joints in such construction the plastic deformation capacity becomes very lower because of the existences of scallops at the beam end for welding especially under alternately repeated cyclic bending In order to make clear the existing ductility of beam to column joints in steel concrete composite construction, especially in steel profile encased reinforced concrete construction, the low cycle fatigue fracture tests under alternately repeated cyclic bending are carried out by the loading system shown in Fig. 1 with various constant deflection amplitudes on various types of joints, i. e. column to beam joints (C-Butt), beam to column joints (B-Butt) and beam to column joints with scallops (B-Butt-Sc) illustrated in Fig. 2. The low cycle fatigue fracture limits of such various types of beam to column joints in steel profile encased reinforced concrete construction are summerized and illustrated in Fig. 3 in comparison with some other joints such as reinforced concrete (RC), steel (S-B-Butt-Sc) and composite (Comp-B-Butt-Sc) construction. This figure shows very clearly the lack of ductility by the existence of scallops in joints for welding. The brittle fracture modes in encased steel elements are illustrated in Fig. 4.