Fire Test And Analysis Of Concrete Composite Box(Light Box Type)Net Joint Floor

The concrete composite box net joint floor is one kind of new-style floor, it is composed of the small prefabricated component with the cast-in-place concrete rib beam(net form), it has advantages of smooth feet, large cavity and taking load together. According to the floor above are cast-in-place layer, floor is divided into light and dark boxes type.Due to the advantages of large span, light weight, convenient construction and comprehensive cost, It has been widely applied in the practical engineering and the good economic benefit is obtained. However at present there is little experimental study on this structure type at home and abroad, let alone the performance of the fire resistance.In order to do it, the behaviors of the floor with four simply supported conditions in fire is studied. In addition, the vibration performance of the floor before and after the fire are analyzed, the main contents of the paper are as following:According to international standards TSO834heating curves, the test on the floor (light box type)was carried-out in the real fire conditions under a static load equal to2kN per square meter with modified furnace. The temperature distribution throughout the rib beam and composite box, the steel temperature, internal and external plane deformation, the rotation on the edge as well as the natural vibration properties before and after the fire were accurately collected. Connection with the test macro-phenoment, the test data was well analysized, and the damage mechanism, laws of temperature field and displacement change-ment with time and temperature were achieved.Through the test on the concrete composite box net joint floor, we can get the following conclusion: (1) Due to the joint action of the pressure in the plane caused by the temperature and external pressure by the expansion of the gas inside the cavity, the composite box floor generation blowout and instability, then the concrete fall off.(2) Due to the generation blowout of the composite box floor, the structure form of the floor changed to a similar to the ribbed beams floor structure from the hollow floor structure. And it led to the internal force redistribution.(3) Along with the composite box floor blowout, the stiffness of the floor reduced obviously. When most of the floor after burst, the stiffness reduced rate slows. At this time, the stiffness of the floor is mainly caused by the variation of material properties after the fire.(4) When the fire last to90minutes, because of the pressure in the plane caused by the high temperature and external pressure of the plane caused by the pressure difference in and out the test furnace, the composite box roof also generation blowout. Finally, the floor was burned through and lost functions.(5) After the composite box floor generation blowout, the beam was in three face state by fire. Because the side wall has a certain protection to the beam, the heat transfer within the rib beam was slowed down, and then the fire resistance and the refractory limit of the rib beam improved.(6) Although the floor is burning through and lose function role, the whole structure still remain intact integrity because of the rib protected beam and a good fire resistance.