多种屈曲模态下冷弯薄壁开口截面不锈钢构件统一设计理论的研究

There is no clear boundary between the strength failure and buckling failure and between different buckling modes because of the strong nonlinear constitutive of stainless steel. The failure of members presents a coupling of multiple buckling modes. Therefore, the traditional design theories of members based on the single failure mode encounter more obstacles in the design of stainless steel structures. This project focuses on the cold-formed thin-walled stainless steel members with open section, and breaks through the traditional design concept to search for a new theory of the stainless steel structure design. The impact of cold working on the material properties is investigated by the test methods, and the refined model of mechanical properties of stainless steel is built, which the cold working effect is considered. The residual stress and initial imperfection of members are tested and analyzed, and the distribution models of the initial state of the members are proposed. The tests are carried out to study the behavior response of members under the multiple buckling modes, and the criterions of member failure are proposed based on the displacement or energy principle. According to the combination of material model and initial state of the members, the comprehensive index (generalized slenderness) is put forward to characterize the multiple buckling modes. The DSM model of the members considering the multiple buckling modes is established based on direct strength method. The bearing capacity and generalized slenderness of the members are associated to obtain the united-design theory of the cold-formed thin-walled stainless steel members with open section. The achievements of this project are of great social and theoretical value, and will provide the key theory base for the next generation of design code for stainless steel structures.

不锈钢的强非线性本构导致构件强度破坏与屈曲破坏及各屈曲模态之间无明显界线，构件破坏呈现出多种屈曲模态耦合。因此，基于单一破坏模式的传统构件设计理论在不锈钢结构设计中遇到了“瓶颈”。本项目以冷弯薄壁开口截面不锈钢构件为研究对象，突破传统设计理念，寻求不锈钢结构设计新理论。通过试验方法，考察冷加工对材料性能的影响，构建考虑冷加工影响的不锈钢材料力学性能精细化模型；测试与分析构件残余应力和初始缺陷，给出构件初状态的分布模型；试验研究多种屈曲模态下构件行为反应，基于位移/能量原则提出构件破坏判别准则；融合材料模型和构件初状态，凝聚出表征构件多种屈曲模态的综合指标（广义柔度系数）；采用直接强度法，建立考虑多种屈曲模态的构件DSM模型；关联构件承载力和广义柔度系数，形成冷弯薄壁开口截面不锈钢构件统一设计理论。研究成果将为下一版《不锈钢结构设计规程》提供关键理论基础，具有重要的理论价值和社会意义。

不锈钢用于建筑结构中可从材料层面上根本解决钢材易腐蚀难题，且不锈钢结构具有造型美观、易于维护、全寿命周期成本低等优点，日益成为严苛环境下建筑结构的优选方案。不锈钢早期在建筑结构中主要应用于冷弯薄壁构件（如卷边C形截面）。然而，不锈钢材料本构的强非线性导致此类构件强度及不同屈曲破坏模态之间无明显界线，构件破坏常呈现出多种屈曲破坏模态的耦合。基于单一破坏模式的传统构件设计理论在不锈钢结构设计中遇到了较大“瓶颈”。为此，本项目以卷边C形截面不锈钢构件为研究对象，突破传统设计理念，寻求不锈钢结构设计的新理论。首先，基于奥氏体S30408不锈钢，对平板区和转角区材料开展力学性能拉伸试验研究；试验结果表明：修正的两阶段Ramberg-Osgood模型可很好地模拟不锈钢材料的应力-应变关系，冷加工效应对不锈钢材料强度有明显的提高作用。其次，对卷边C形截面不锈钢梁和柱承载力开展了大量的试验研究（12根局部屈曲梁、16根畸变屈曲梁、20根局部-畸变相关屈曲梁、20根整体-畸变相关屈曲梁、20根局部-整体相关屈曲柱、21根畸变-整体相关屈曲柱及19根局部-畸变相关屈曲柱），揭示各试件的破坏过程、破坏现象及屈曲波发展过程，获取了各试件跨中位移、加载点竖向位移、两端转角、纵横向应变，及试件的屈曲荷载和极限承载力，重点考察了屈曲长细比对试件屈曲承载力的影响。再次，通过程序模拟再现不锈钢试件承载力试验过程，结合构件边界条件和材料性能参数，构建了不锈钢构件承载力计算模型；开展了大量的参数化有限元模拟分析，剖析了构件承载力的多种影响因素。最后，基于直接强度法，提出了多种屈曲模态下卷边C形截面不锈钢构件承载力的统一计算方法。本项目研究成果对不锈钢结构承载力计算理论的凝练、设计建议与构造措施的提出，及设计标准的制定具有十分重要的社会价值和理论价值。