现浇混凝土空心楼盖抗火性能的研究

The cast-in-situ concrete hollow floor, as a new structural system vigorously promoted by the country, combines the merits of the cast-in-situ concrete floor and the pre-cast hollow floor. This study intends to conduct further fundamental studies on the cast-in-situ concrete hollow floor from the aspect of its fire resisting performance. Based on the achievements of studies on the fire resisting performance of the conventional cast-in-situ concrete floor, the applicant started from testing the fire resisting performance of the cast-in-situ concrete hollow floor with different internal mould and supporting means to study its mechanical behavior in a fire, to observe its cracking expansion rule and failure mechanism, and to analyze if the cracking way conform to the plastic hinge line theory; according to the mechanics principle of finite deformation, the relationship between the Kirchhoff stress increment and the Green strain increment under high temperature was established, to study the behavior rules of the cast-in- situ concrete hollow floor in various boundary conditions as well as with different internal molds and cavity heights in case of fire through conducting the finite element analysis for the non-linear deformation of the cast-in-situ concrete hollow floor;finally, Proposed design method of fire resistant for the cast-in-situ concrete hollow floor and control technology to improve its fire resistance. The research achievements of this study can provide fundamental key data and scientific basis for the promotion and application of the cast-in-situ concrete hollow floor.

现浇混凝土空心楼盖兼有现浇混凝土楼盖和预制空心楼盖的优点，尤其适合在大跨度结构中应用，是国家推广的新型结构体系，本课题拟从现浇混凝土空心楼盖抗火性能侧面进一步展开基础研究。 申请者在传统现浇混凝土楼盖抗火性能研究成果的基础上，首先开展不同空腔形状和支承方式的现浇混凝土空心楼盖抗火性能的试验，研究其在火灾中力学性能的劣化规律，考察裂缝的开展规律和楼盖的破坏机理，分析裂缝开裂方式是否符合塑性铰线理论；其次根据有限变形力学原理，建立高温下应力增量与应变增量间的关系，提出对现浇混凝土空心楼盖进行非线性大变形有限元分析的单元模型，研究火灾作用下空腔形状和边界条件对现浇混凝土空心楼盖力学行为的影响规律；最后基于试验研究和理论分析结果，提出现浇混凝土空心楼盖抗火设计的方法和提高其抗火性能的控制技术。 该课题的研究成果可以为现浇混凝土空心楼盖的推广应用提供基础性的关键数据和科学依据。

现浇混凝土空心楼盖兼有现浇混凝土楼盖和预制空心楼盖的优点，尤其适合在大跨度结构中应用，是国家推广的新型结构体系，研究项目从现浇混凝土空心楼盖抗火性能侧面进一步展开基础研究。.项目研究内容是：首先对不同支承方式的现浇混凝土空心楼盖抗火性能进行试验试验，研究其在火灾中力学性能的劣化规律，考察裂缝的开展规律和楼盖的破坏机理，分析裂缝开裂方式是否符合塑性铰线理论；其次根据有限变形力学原理，建立高温下应力增量与应变增量间的关系，提出对现浇混凝土空心楼盖进行非线性大变形有限元分析的单元模型，研究火灾作用下空腔形状和边界条件对现浇混凝土空心楼盖力学行为的影响规律；最后基于试验研究和理论分析结果，提出现浇混凝土空心楼盖抗火设计的方法和提高其抗火性能的控制技术。.重要结果如下：.（1）现浇空心楼盖在火灾作用下，试验板的板底受热开始膨胀，由于肋梁的存在，使得底板在膨胀时产生约束作用，从而在试验板的板底处产生压应力。随着炉温的升高，热量通过板底逐渐向模盒的空腔内传递，使得模盒内的气体温度升高，压强增大，底板在各种因素作用下开始碎裂、脱落。.（2）现浇空心楼盖经历了高温3小时多，在长时间高温作用下试验板并没有被烧穿，试验后刚度恢复比超过70%，说明空腔的刚度很小，空心楼盖具有很好的抗火性能。.（3）现浇空心楼盖在火灾作用时，肋梁内均分布有非线性的温度场，从试验板底到试验板顶温度梯度逐渐递减。.（4）柱支承楼盖节点破坏严重，柱内侧混凝土被压碎，边梁受扭产生较多裂缝，柱上部楼盖表面产生许多裂缝。.（5）试验板在温度和荷载作用下会产生平面外的竖向位移，并且随着火灾燃烧的时间增长而变大。四边简支的试验板最大位移出现在板中心点处，最大位移出现的时间在停火后产生，这就说明楼板在发生火灾后最先破坏的是停火后的中心点处。.该课题的研究成果可以为现浇混凝土空心楼盖的推广应用提供基础性的关键数据和科学依据。