风和强震作用下高耸高层钢结构焊缝疲劳劣化机理与寿命预测方法

The welded joints on tall steel structures under winds and earthquakes are susceptible to cumulative fatigue damage, which may induce welded joints damage or entire structure collapse. However, up to now, no reliable fatigue life prediction methods for welded joints were developed throughout the world. In this project, the topic of the fatigue deterioration mechanism and the fatigue life prediction methodology of welded joints on tall steel structures under winds and earthquakes will be promoted. The emphasis is placed on the two frequently appeared fatigue damages including the multi-axial high-cycle stress fatigue and the multi-axial low-cycle plastic-strain fatigue. Firstly, the multi-scale simulation methods of elastic stress and plastic strain in welded joints on tall steel structures under winds and earthquakes will be proposed. Then, the generation mechanism, the distribution pattern and the relaxation model of welding residual stress in welded joints will be discussed. Subsequently, the mathematical and mechanical models of equivalent fatigue damage indexes that are adopted to describe the multi-axial high-cycle stress fatigue and the multi-axial low-cycle plastic-strain fatigue under winds and earthquakes will be established. After that, the failure mechanism of the multi-axial high-cycle stress fatigue and the multi-axial low-cycle plastic-strain fatigue in welded joints on tall steel structures under winds and earthquakes will be extracted. Finally, integrating the S-N curves obtained by experiments, the fatigue life prediction methodology of welded joints on tall steel structures under winds and earthquakes will be presented. The results deduced in the project can provide the theoretical basis for the wind-resistance design and the earthquake-resistance design of welded joints on tall steel structures.

在风和强震作用下，高耸高层钢结构焊接结点焊缝极易产生疲劳损伤累积，造成焊接结点的破坏甚至整个结构的倒塌，但国内外对此仍缺乏可靠正确的预测方法。本项目围绕风和强震作用下高耸高层钢结构焊缝疲劳劣化机理与寿命预测这一主题，针对不同应力水平下极易出现的焊缝高周弹性应力疲劳和低周塑性应变疲劳问题，提出风和强震作用下高耸高层钢结构焊接结点焊缝弹性应力和塑性应变的多尺度模拟方法，揭示焊接结点焊接残余应力场的产生机理、分布模式和松弛规律，建立风和强震作用下焊接结点焊缝多轴高周弹性应力疲劳和多轴低周塑性应变疲劳等效损伤参量的数力学表征，揭示风和强震作用下高耸高层钢结构焊接结点焊缝多轴高周弹性应力疲劳和多轴低周塑性应变疲劳的破坏机理，最终结合试验S-N曲线形成风和强震作用下高耸高层钢结构焊接结点疲劳寿命预测方法。研究结果可为高耸高层钢结构焊接结点的抗风和抗震设计提供依据。

在风和强震作用下，高耸高层钢结构焊接结点焊缝极易产生疲劳损伤累积，造成焊接结点的破坏甚至整个结构的倒塌，但国内外对此仍缺乏可靠正确的预测方法。本项目提出了风和强震作用下高耸高层钢结构焊接结点焊缝弹性应力和塑性应变的多尺度模拟方法，揭示了焊接结点焊接残余应力场的产生机理、分布模式和松弛规律，建立风和强震作用下焊接结点焊缝多轴高周弹性应力疲劳和多轴低周塑性应变疲劳等效损伤参量的数力学表征，揭示风和强震作用下高耸高层钢结构焊接结点焊缝多轴高周弹性应力疲劳和多轴低周塑性应变疲劳的破坏机理，最终结合试验S-N曲线形成风和强震作用下高耸高层钢结构焊接结点疲劳寿命预测方法。结果表明：焊接残余应力与动力荷载引起应力迭加时，动力荷载引起工作应力与焊接残余应力叠加后应力状态不超过屈服强度时，焊接残余应力基本稳定，不会发生重分布或松弛现象；焊接残余应力叠加动力荷载引起工作应力超过屈服强度时，那么超过屈服应力的残余应力部分将会释放并发生重分布，即发生焊接残余应力的松弛；动力荷载引起工作应力超过材料的实际屈服强度进入塑性阶段，焊接残余应力基本上会松弛至很低的水平，或完全消除；在低应力幅下，应力比或平均应力对疲劳寿命影响明显，不可忽略；考虑平均应力效应，根据M-S-N法计算的疲劳寿命明显低于规范方法，更接近实际构件疲劳寿命；强震下梁柱焊接结点的部分梁柱端要进入塑性，为保证三种有限元尺度中的梁柱梁单元在弹性阶段工作，焊接结点建立的实体有限单元应包括部分梁柱端；风力作用下高耸钢结构焊接结点焊缝处会产生“焊接-风致”应力，“焊接-风致”应力要大于纯风致等效应力，小于焊接残余应力和风致等效应力简单迭加的应力，且一般不会超过材料的屈服强度；高耸钢结构的焊接结点焊缝处的“焊接-风致”应力相当于提高了该位置的平均风应力响应，但它以不超过材料的屈服强度为界限。研究结果可为高耸高层钢结构焊接结点的抗风和抗震设计提供依据。