Analysis Of A Collapsed Underground Reinforced Concrete Slab-Column Structure And Anti-collapse Design Recommendations

The slab-column structure began to develop rapidly and replace part of the beamplate structure for it can reduce the height of the structure,save space,and facilitate pipeline construction;besides,the bottom of the plate is simple and beautiful,it has been gradually adopted by the builder,However,in recent years,there has been the successive collapse of slab-column structure basement in the construction process,resulting in huge economic losses and safety-oriented accidents.For the given facts above,some local governments have put up tricter review on the structural form of reinforced concrete beamless floors.According to the modeling analysis of the actual component section,material strength,design load and actual load on the accident of project A and B,the bearing capacity was reviewed from the bending,shearing,column cap punching,etc.,and it was found that the basement roof was uniformly designed.The flexural,shear and punching resistance bearing capacity of the column caps under the covered soil load conditions meet the requirements of the specification,but the column caps will suffer punching failure when a certain percentage of the local overburden is overloaded.By using the ABAQUS finite element software,the elastoplastic damage simulation of the top slab structure of the basement under the uniform design of the overburden condition and the partial overburden overload condition of Project A was carried out,and the uniform load was compared with various unbalanced stacking loads.The simulation results under working conditions show that unbalanced stacking load will aggravate the damage of the structure,and several unfavorable overload conditions are listed.The original reinforcement of the structure and the reinforcement calculated after considering the adverse layout effect are in various working conditions.The original design scheme and the optimization scheme of adding bent steel bars are simulated for Project B under overload conditions.Both conditions belong to punching failure,but the punching resistance bearing capacity of the joints is significantly improved after the bent steel bars are added.As we review the bending bearing capacity and thrust cutting bearing capacity of the joint about accident project B,it is indicated that the thrust cutting bearing capacity of the joint does not meet the need of the design.The elastic-plastic damage simulation comparison of the original design joint and the joint after the optimization scheme is given for the typical plate column joint of collapse case B,the optimized joint structure model has various bearing indexes superior to the original joint,further verifying the accuracy of the optimization scheme.Through the above analysis,several design suggestions are put forward: 1)When designing the roof of the basement slab-column structure,the structural designer needs to carry out the flexural bearing capacity,punching shear bearing capacity and direct shear bearing capacity of the structure according to the design goals;After calculation by the calculation softwares is done,the structural designer should check the calculation,and fully consider the various working conditions that may occur during the construction stage,and put forward construction requirements in the description of the design drawing;2)It is recommended that the column cap be equipped with measures such as bent steel bars or shear stirrups to resist the additional punching force from the unbalanced bending moment caused by the uneven stacking of the roof during the construction process,and prevent the continuous collapse resulted from the damage of the plate-column structure node.