Study On Mechanical Behavior And Collapse For A Beamless Foor Subjected To Vertical Load

In recent years,the occurrence of the structural progressive collapse has not been uncommon.foreign and domestic researchers have extensively studied the progressive collapse behavior of reinforced concrete structures.The existing research mainly focuses on the progressive collapse ofbeam-column structures,such as steel structure or concrete frame,but there are few studies on the progressive collapse of reinforced concrete beamless floor structure.As a common structural form,the beamless floor structure has the advantages of costs reduction and fast execution,but the potential risk factors for its continuous collapse are more complex and more dangerous than the traditional structure.Therefore,it’s very important to study the mechanical behavior and progressive collapse of the beamless floor structure.This paper by the using of finite element analysis software ANSYS simulation and combining with a real engineering accident studied the mechanical behavior and progressive collapse of the beamless floor structure subjected to vertical load.The main contents and conclusions of this paper are as follows:(1)In this chapter,the test specimens in the literature weresimulated,and the experimental results in the literature were taken as reference to verify the accuracy and rationality of the finite element software ANSYS simulation.This chapter put forward the modeling method,parameter selection and calculation method suitable for the finite element analysis in this paper,which lays the foundation for the finite element analysis of the full text.(2)In this chapter,static analysis was performed on the one-span beamless floor structure in the collapsed area and the material parameters were selected according to the design value.This chapter mainly studied the mechanical behavior of slab in the unbroken,cracked,and broken states.At the same time,the effect of concrete curing time on structural bearing capacity was analyzed by changing the material properties.This chapter provided theoretical support for the subsequent overall analysis.The analysis showed that the slab exhibit obvious strip characteristics when they are not cracked or cracked;The structure is mainly controlled by cracks during normal operation stage,and it is mainly controlled by displacement during the broken stage;The earliest cracks at the top of the slab appeared at the center of the slab,they appeared in the form of two orthogonal crosshairs and developed continuously from the center of the slab.The earliest cracks at the bottom of the slab appeared in the middle of the edge of the slab and gradually developed into long cracks along the edge of the slab.(3)In this chapter,the finite element analysis software ANSYS was used to establish the finite element model of collapsed area structure.With the boundary condition and the concrete strength as the parameters,four different working conditions were set up.Analyzed the mechanical behavior of the structure under different cover soil thickness and different positions of the car in each working condition.Through the comparison and analysis of the four conditions,the influence of the boundary conditions,concrete strength,position of the car,and the thickness of the cover soil on the collapse of the structure was studied.The analysis showed that the influence of the boundary conditions on the collapse of the structure is higher than concrete strength;The location of the car and the thickness of covering soil are external factors that affect the collapse of structures,and their influence on structural collapse is mainly limited by boundary conditions.When the structure appears free end,the position of the car and the thickness of the overlying soil will become the main factor that affects the collapse of the structure.(4)The object of analysis in this chapter is a 2×2 span beamless floor structure in the collapsed area,and the finite element model was built using ANSYS software.This chapter mainly studied the dynamic and static characteristics,failure process,and load characteristics of the slab subjected to vertical load after the middle column is dismantled.The analysis showed that when the dynamic analysis is adopted,the deformation and internal force of the structure are remained to the stable state after 0.4s.It is proved that the anti collapse ability of the structure is better.When the static analysis is used,the slab is loaded continuously to the limit state,and the ultimate load value of the structure is 31kN/m~2.At the same time,this chapter also analyzed the law of the deformation and crack development of the plate during the static loading process,and the criterion of structural progressive collapse is established based on the end angle of the plate at the limit state.(5)This chapter based on the results of the finite element analysis of the actual project,combined with the design method of structural resistance to continuous collapse,propose the measures to prevent the progressive collapse of the structure from two aspects of architecture and structure.