Study On Fire Behavior Of Multi-span Concrete Composite Box Beam Floor

The use of fire promote the progress of human society, it is a manifestation of human civilization, but if the fire that can not be control by human has become a disaster. The building fire made the most serious losses, the losses caused by building fire accounted for80%[1] of all fire losses, so it is necessary to study the fire resistance of buildings. Reinforced concrete roof in the fire can cut off and actively prevent the spread of fire the upper floors, but because of the fire larger, it is usually severe the most damage in the fire. Concrete Composite cages beam floor is a new form of floor structure, it has been applied to many major projects, and it has already made great economic and social benefits, but the flat floor slab of concrete composite cages under fire behavior research is still in its infancy. Though the behavioral of Concrete Composite Box Beam Floor has been changed under fire, get the temperature variation and failure modes of the net beam floor, in the design and construction process can take the necessary protective measures to mitigate fire damage to the structure, to reduce casualties and economic losses. Therefore, concrete composite box beam floor in fire behavior change research has practical significance. The actual project network beam floor for multi-span structure, this test is mainly for multi-span Mixed Concrete Composite cages beam floor fire behavior. Use the fire test furnace,2×3cross-concrete composite box beam floor real fire tests in accordance with ISO834international standard temperature curve, By analyzing the failure characteristics of composite box beam floor, the fire effect, the board deformation and temperature variation of the following conclusions:In the role of high temperature of the furnace, the laminated floor box appears thermal expansion, the superimposed box cavity temperature rises to a sharp increase in air pressure, however, due to the superimposed box around the beam base plate there is a strong constraint, make the floor by pressure, the cavity pressure make the base plate subjected to the biasing force of the outer plane, the floor in the heating process can easily burst, and it makes a circular damage zone around the burst bottom, external loads under pressure laminated bottom plate, more likely to have burst under the combined effect of load and fire, the floor burst exposed wire under high temperature buckling. Because the evaporation of water take away a lot of heat, concrete and steel board temperature reaches100℃C for some time flat segment, higher up from the board at the end of this phenomenon is more obvious, so the moisture content of the concrete ribbed temperature field distribution of impact, thus affecting the fire resistance performance of the board, net flat floor slab of concrete and steel change, there will be a certain degree of hysteresis due to the thermal inertia of the concrete, and the highest value of the temperature of concrete and reinforced after the cease-fire, rather than ceasefire moment, fire, ribbed temperature field distribution obvious gradient, and larger than the average on three sides by fire beams, early in the fire, burst superimposed bottom plate, the lower floor stiffness, the deflection increases, but with the rise of temperature in the furnace, ribbed cross-section have a greater temperature gradient, the phenomenon of anti-arch in the floor, side frame beams under load, its stiffness and small changes from the mid-span vertical forward to the displacement and vertical displacement after the cease-fire has a certain proportion of reply, composite plate of the bottom of the burst, the structure of the force system change into a waffle slab floor without beam system, the structure of redistribution of internal forces generated edge beams of the floor by the torque effect, resulting in a diagonal cracks; temperature stress due to the presence of a temperature gradient within the board, the upper floor produce more cracks, close to the center of the local network beam floor area inside closed or nearly closed cracks, As the temperature increases, the composite box and ribbed damage, more and more serious, the floor crack gradually reduced, the coupling of the fire load in the middle column around the center nearly closed ring cracks in the four corners of the floor, arc-shaped cracks, vertical cracks in the column ribbed edge, stop burning after some time ribbed more uniform temperature distribution, this phenomenon is more obviously.