EXPERIMENTAL STUDY ON FIRE RESISTANCE OF REINFORCED CONCRETE SUPERIMPOSED SLABS WITH FOUR SIDES SIMPLY SUPPORTED BY STEEL BAR TRUSS
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摘要: 钢筋桁架混凝土叠合楼板由预制混凝土底板、钢筋桁架及现浇混凝土后浇层组成。预制板块间设置混凝土现浇带，受力钢筋在现浇带处搭接连接，形成整体楼板。通过4块四边简支钢筋桁架混凝土叠合板抗火试验，研究了叠合板在火和荷载耦合作用下的火灾行为，试验中考虑了不同后浇叠合层厚度和不同预制板拼装方式。结果表明：钢筋桁架混凝土叠合板在高温-荷载耦合作用下，预制底板与叠合层未产生明显脱离现象，火灾时叠合板仍具有较好的整体工作性能；板上表面沿现浇带与预制板结合面及钢筋桁架将产生纵向裂缝，最终结合面形成贯通裂缝，楼板被烧穿达到耐火极限，试验板的耐火极限均达到3 h；火灾时现浇板带板底混凝土爆裂严重，现浇带处采用搭接方式连接的钢筋外露，失去作用，双向板受力机理发生变化，形成由预制板和现浇带组成的沿预制板跨方向的单向板带，承载力大幅降低，火灾时板的剩余承载力宜按单向板计算；后浇层厚度小，预制板宽大、拼缝少，耐火极限短；钢筋桁架对保证火灾时叠合层与预制层共同工作起到关键作用。Abstract: The reinforced concrete superimposed slabs with steel bar truss are composed of prefabricated concrete bottom slab, steel bar truss and post-cast-in-situ composite layer. Concrete cast-in-place belts are set between prefabricated slabs, and the longitudinal reinforcements are lapped and connected at the cast-in-place belt to form an integral floor slab. To study the fire behavior of laminated slabs under high temperature-load coupling effect, fire-resistance tests are performed on four sides simple supported superimposed slabs with different thickness of post-casting layer and assembling modes. The results show that under the high temperature-load coupling effect, there is no obvious separation between the prefabricated bottom plate and the laminated layer, and the laminated plate still has good overall working performance during the fire. Longitudinal cracks appear on the surface of the slab along the joint surface between the cast-in-situ belt and the prefabricated slab and along the steel truss. The final joint surface forms through cracks, and the floor slab is burned through and reaches the fire resistance limit. The average fire resistance limit of the tested board is up to 3 hours. During the fire exposure, the concrete at the bottom of the cast-in-situ slab spalls seriously, and the steel bars connected to the lap joint at the cast-in-situ zone are directly exposed to fire and lost their effect, which greatly reduces the bearing capacity of the one-way slab in the same direction, and the residual bearing capacity of the slab should be calculated according to the one-way slab under the fire exposure. Due to the small thickness of the post-casting layer and the large width of the prefabricated slab with few seams, the fire resistance limit is shorter. The steel truss plays a key role in ensuring that the laminated layer and the prefabricated layer work together under the fire exposure.
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Key words:
- concrete superimposed slabs /
- four-side support /
- steel bar truss /
- fire resistance /
- experimental study
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图 5 试件温度测点热电偶布置 /mm
Figure 5. Layout of thermocouples at temperature measuring points of specimens
图 6 混凝土温度测点沿截面布置(括号内数据为DHB-3、DHB-4)
Figure 6. Layout of concrete temperature measuring points along the section (Data in brackets are DHB-3, DHB-4)
图 13 试件受力钢筋测点温度-时间关系曲线
Figure 13. Rebar temperature-time curves at each measuring point
表 1 试件主要参数及要求
Table 1. Main parameters and requirements of specimens
试件号 预制底板尺寸/mm (数量) 试件尺寸/mm 后浇层厚度/mm 拼缝宽度/mm 保护层厚度/mm DHB-1 900×3600(3) 3600×3600×130 70 450 15 DHB-2 900×3600(3) 3600×3600×150 90 450 15 DHB-3 1600×3600(2) 3650×3600×130 70 450 15 DHB-4 1600×3600(2) 3650×3600×150 90 450 15 
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