| If the frame column is destroyed, progressive collapse may happen in the building, causing serious casualties and economic losses, so how to prevent the progressive collapse has become one of important issues for structure Engineering. Ductility is one of the main factors to prevent the vertical progressive collapse of the building, so the building should avoid shear failure prior to bending failure.The load coming from the secondary beam and cast-in-place plate in 1/4 span, 1/2 span, 3/4 span by the imposition of weight on the reinforced concrete beams fixed at both ends has been simulated, and the case that reinforced concrete frame beams doubled has been simulated when reinforced concrete frame beam loses mid column in the side at the midspan by automatic detacher. It studies dynamic response and shear failure mechanism when reinforced concrete frame column damaged suddenly, and experimental results indicate that: damage patterns of beams KJL01, KJL02 are bending failure, and damage patterns of beams KJL-2, KJL-3, KJL-4 are shear failure. The values of bending DCR are between 1.7 and 1.9, and shear DCR are not more than 1.2. When the beam occurs shear failure, the arch effect can't bring into full play, and consequently makes the ultimate capacity of beam lowering, so the building must configurate reinforced in the building design to resist progressive collapse in accordance with "strong shear weak bending".Dynamic response of single degree of freedom without damping elastic-plastic system has been analysed, the results show that: the value of bending DCR of elastic-plastic system has something to do with the ductility factorβ, whenβ=2 and the value of DCR is 0.75. Dynamic response of single degree of freedom elastic damping system has been analysised to find that the time to the maximum displacement has nothing with loading time only depending on the natural cycle T of the building, the shortest time when the system goes into Plastic stage and without undermining is T/4.
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