轻质、超高韧度水泥基复合材料保护下钢构件的抗火性能研究

Subjected to environmental impact, service load, seismic load or even explosion, common fire insulation material will be cracking or even drop off from protected substrate. Deteriorated protection is supposed to an impair or even totally loss of fire insulation capacity.The applicant here took part in a project of developing novel engineered cementitious composites.Besides the common characteristics of normal fire insulation material, such as light-weight and low thermal conductivity, this new material is, in fact, a special ultra-high toughness cementitious composites (UHTCC), which shows strain-hardening under large strain level (no less than 3%). At the same time, it can be triggered out multiple cracks with average width of no more 70 μm. In this way, UHTCC insulation material will not drop off under extreme loads and keep the stable thermal property under fire. The key point of this proposal is to study on how to trigger multiple cracks of UHTCC fire insulation when working with steel structure exposed to external loads. First of all, the interfacial fracture mechanism will be experimentally studied, including the mode I and II interfacial fracture behaviors between UHTCC and steel substrate and also the decoupling of mixed fracture. Digital image correlation (DIC) method will be adopted to track the progressive crack propagation. The corresponding algorithm will be derived based on DIC continuous measurement. The design theory of mutiple-crack trigger is to be established on UHTCC insulation. As the experimental part, various loading patterns, including static load, cyclic loads and impact load are planned to apply to the UHTCC protected steel specimens and the post-loaded specimens will be exposed to real fire to verify the influence of UHTCC insulation after loading. The effects of different level of insulation thickness, the size effect of steel structure and the fracture boundary condition are compressively considered in test and also in the following theoretical analysis. According to the test data of fundamental fracture behaviors and structural tests,the extended finite element method (XFEM) and cohesive interfacial fracture will be employed to establishe a performance-based design method for a variety of fire-resistance requirements.

在环境的侵蚀、正常使用荷载、地震荷载甚至是爆炸荷载的冲击下，普通的厚型防火材料会开裂甚至大面积脱落，导致防火功能的弱化甚至是丧失。申请者参与开发的新型材料，除具备轻质和良好的热工性能外，还具有超高韧度水泥基复合材料特有的力学性能：受拉应变达3%后，仍保持应变强化，细密裂缝的平均宽度不超过70μm，难以脱落，并保证热工性能的稳定。对于超高韧度材料，如何激发细密裂缝，保证其防火保护功能的完整性是研究重点。首先研究材料与钢材界面的基本断裂性能，包括I型、II型以及混合型界面断裂。通过数字图像相关技术测量能量释放率，提出相关的计算公式。其次，进行超高韧度防火保护的设计方法的研究，考虑不同耐火设计要求、荷载组合、钢构尺寸以及边界条件下的超高韧度材料的界面及本体力学反应，进而预测防火保护性能的变化。通过力学及火灾试验来验证提出的设计方法，并采用扩展有限元及内粘聚模型进行模拟和公式的扩展。

在环境的侵蚀、正常使用荷载、地震荷载甚至是爆炸荷载的冲击下，普通的厚型防火材料会开裂甚至大面积脱落，导致防火功能的弱化甚至是丧失。申请者参与开发的新型材料，除具备轻质和良好的热工性能外，还具有超高韧度水泥基复合材料特有的力学性能：.1) 成功研发了拉伸应变强化、超轻型钢结构防火涂料，材料的受拉应变达 3%，密度小于800kg/m3，开裂后细密裂缝的平均宽度不超过 70μm，并具有良好的热工性能。.2）研究材料与钢材界面的基本断裂性能，包括 I 型、II 型以及混合型界面断裂。通过数字图像相关技术测量能量释放率，提出相关的计算公式。.3）进行超高韧度防火保护的抗火试验和设计方法的研究，通过力学及火灾试验来验证提出的设计方法，并采用有限单元法进行了参数扩展分析。