基于微观力学模型不同方式成型圆钢管的屈曲后断裂机制

As a cross section with a rational material distribution, circular hollow sections (CHS) have been widely applied to structural systems such as frames and trusses, and hysteretic properties of CHS members are of significant importance to seismic performance of these structures. Post-buckling cracking of CHS members has been reported in recent strong earthquakes. There is an urgent need to investigate the cracking mechanisms and their effects on seismic performance of the members. In addition, there are several manufacturing methods for CHS, which can be generally classified into cold-formed and hot-formed. The main analytical object in this study is steel CHS members. Effect of manufacturing methods on global buckling, local buckling, ductile fracture and seismic performance of uniaxially loaded CHS members, will be comprehensively investigated by employing experimental and numerical approaches simultaneously. This study aims to clarify failure mechanisms of cold-formed and hot-formed CHS members under cyclic large strain loading; the coupling effects among global buckling, local buckling and ductile fracture; main factors affecting hysteretic properties of the members. Finally, a design proposal for seismic design of the uniaxially loaded members based on performance indices, i.e., load-carrying capacity, ductility and absorbed plastic energy capacity, will be presented. The expected achievements are of significant academic and practical importance to advancement in the design accuracy of Chinese steel structures, and improve the performance-based seismic design method.

圆钢管作为材料分布合理的截面，在框架和桁架等结构体系中有着广泛的应用，该截面构件在大塑性滞回加载下的性能对结构安全性至关重要。在近年来发生的大地震中，圆钢管截面构件的屈曲后断裂时有发生，其断裂机理及抗震性能丞待研究。此外，圆钢管的加工工艺呈现多样化，大致可以分为冷成型及热成型两大类。本课题将以圆钢管截面构件为主要研究对象，以试验和数值相结合的方法，系统研究成型方式对其在单轴加载下整体屈曲、局部屈曲、延性断裂以及滞回性能的影响。本课题将细致、系统揭示圆钢管截面构件在单轴大塑性循环加载下的破坏机理，屈曲和延性断裂之间的相关关系，以考察成型方式对圆钢管屈曲后断裂性能的影响；总结单轴加载下圆钢管抗震性能的主要影响因素；并最终基于承载力、延性、耗能能力等主要性能参数提出单轴加载下圆钢管截面构件抗震设计建议。预期成果对有效提高我国钢结构的设计精度，完善基于性能的抗震设计方法具有重要的学术和工程意义。

在1994年美国Northridge地震和1995年日本神户地震中，有大量焊接框架建筑钢结构在梁柱焊接节点处发生断裂。高周和低周疲劳破坏的寿命一般在10000圈以上，有别于一般的疲劳破坏，强震下的金属结构断裂破坏一般发生在几圈至几百圈大塑性循环加载之后。相关破坏过程涉及塑性，屈曲，裂纹萌生，裂纹扩展等强非线性行为。本项目研究大塑性循环加载下钢结构的延性断裂机理，从材料弹塑性本构开始研究，在此基础上构建循环加载下金属材料的延性裂纹萌生、裂纹扩展准则，从而准确的定量评估钢结构在地震随机幅值循环加载作用下的损伤断裂性能。以材料、构件单调、滞回拟静力试验、数值模拟和理论研究为方法，同时采用扫描电镜等技术观察研究断面的细观断裂特征，考察了金属材料从材料细观到构件层面的延性断裂机理以及相关数值模拟方法。本项目获得了普通结构钢和Q460高强钢等材料在单调拉伸作用下的全应变域真实应力-真实应变数据，同时获得了普通结构钢在不同加载历史下的滞回本构关系。构建了能够准确描述结构钢在全应变域弹塑性行为的材料滞回模型，以及金属载力在正应力作用下的裂纹萌生和扩展模型。相关研究成果为金属的超低周疲劳寿命评估以及高性能金属结构的设计提供了重要的理论和数值工具。