高温下(后)10.9级高强螺栓蠕变性能研究

Creep behavior of 10.9s high-strength bolts under and after fire

高强螺栓作为钢结构连接中重要的受力部件,应力水平高,高温下易产生蠕变,会导致连接节点发生大变形而破坏,影响整体结构抗火性能。为此,对10.9级高强螺栓在高温下和高温后的蠕变行为进行试验研究,通过DIC测量方法获得不同温度和应力水平下螺栓的蠕变曲线;对破坏的10.9级高强螺栓进行电镜扫描,研究其断口微观形貌和破坏机理;基于试验数据提出了高强螺栓的高温蠕变模型,并针对T形节点抗火性能进行参数分析。研究表明:高温下高强螺栓的蠕变显著,蠕变应变与温度和应力比正相关,但高温后蠕变现象不明显;高温后高强螺栓断口呈杯口状,具有脆性沿晶断裂特征,而高温下螺栓颈缩明显,呈塑性穿晶断裂特征;Field&Field蠕变模型适用于表征高强螺栓高温蠕变性能,温度、荷载和持时是影响高强螺栓高温蠕变的主要因素,螺栓蠕变对钢节点抗火性能影响较大,不考虑蠕变影响偏不安全。

As an important structural component in the connection of steel structures,high-strength bolts have a high stress level and may experience creep deformation under high temperatures.This will lead to excessive deformation and failure of the connections,and affect the global fire behavior of the structure.To this end,experiments were conducted to investigate the creep behavior of 10.9s high-strength bolts under high temperature and after fire.The creep straintime curves at different temperatures and stress levels were obtained using DIC measurement systems.The fracture surface of the damaged 10.9s high-strength bolts was scanned by electron microscope to investigate the micromorphology and failure mechanism of the bolts.A high-temperature explicit creep model was calibrated by the test data,and parametric studies were conducted on a T-type connection.The results show that the creep deformation of high-strength bolts is significant at high temperatures,and the creep strain is positively correlated with the temperature and stress ratio.The post-fire creep effect is minor,and the fracture of the bolts after fire is in a brittle intergranular manner represented by a cup-shaped fracture surface.The necking of bolts under high temperatures is obvious and in a ductile transgranular manner.The Field&Field creep model is suitable for characterizing the hightemperature creep behavior of high-strength bolts.The temperature,stress level,and duration time are the main factors affecting the high-temperature creep of high-strength bolts.The creep of bolts has a great impact on the fire resistance of steel connections,and ignoring the influence of creep can lead to unsafe results.