火灾下膨胀型钢结构防火涂层的破损及其对钢构件升温过程的影响

Physical Damage of Intumescent Coatings and Their Effects on the Temperature Development of Steel Elements

为考察火灾下膨胀型钢结构防火涂层破损模式与程度的影响因素和涂层破损对钢构件温升过程的影响,对钢构件表面涂覆防火涂层组成的试件进行隔热性能试验和标准耐火试验。试验过程中测量并记录钢构件温度,试验结束后统计分析涂层的破损情况。研究结果表明,火灾下膨胀型钢结构防火涂层的破损模式为开裂和界面剥离,涂层脱落发生在降温过程。无荷载板型和短柱试件涂层的破损模式为Ⅰ型细小裂纹和Ⅱ型小裂缝,钢基材截面最大温差与截面平均温度的比值分别小于2.2%和6.3%。轴压长柱试件涂层的破损模式为Ⅲ型与Ⅳ型大裂缝(基材为碳钢)和界面剥离(基材为不锈钢),截面最大温差超过截面平均温度的10%。当采用未加载小尺寸试件涂层隔热性能的检测结果指导足尺加载钢构件的抗火设计时,需对涂层的等效导热系数进行修正以考虑涂层开裂和界面剥离对钢构件温升过程的影响。

To investigate the factors affecting physical damage mode and extent of intumescent coatings under fire and how the damage influences temperature development of steel elements, fire tests are conducted on the specimens which are made by applying intumescent coatings to steel elements.Temperatures of steel elements are measured and recorded during fire tests and the physical damages of intumescent coatings are counted and analyzed after fire test.The studies show that main damage modes of intumescent coatings are cracking and debonding during the heating stage of fire exposure, and extensive detachment happens during the cooling stage.Fine distributed cracks(type Ⅰ) and small discrete cracks(type Ⅱ) are typically seen in plate specimens and unloaded section specimens and the ratios of maximum temperature difference to the average temperature of the cross section are lower than 2.2% and 6.3% for plate and unloaded section specimens, respectively.Medium(type Ⅲ) and large discrete cracks(type Ⅳ) and debonding are observed in loaded column specimens with carbon steel surface and stainless steel surface, respectively.The maximum temperature difference of the cross section is more than 10% of the average temperature.The effective thermal conductivity of intumescent coatings based on the unloaded specimens should be modified to incorporate the effects of mechanical loading induced cracking and debonding on the intumescent coating behavior.