The Study Of The Seismic Collapse Of Reinforced Concrete Frame Structure Considering Soil-Structure Interaction

Rigid foundation assumption is adopted usually in current structural collapse damage study,which ignores the impact of filter and amplification effect by soil to the seismic responsecharacteristics and collapse process of superstructure. And seismic response analysis of framestructures direct at elastic-plastic deformation stage, the research of structure collapse damage isless. So the study of reinforced concrete frame structure collapse considering soil-structureinteraction is importance and practical significance.Through describing lots of related literatures, present situation of reinforcedconcrete frame structure collapse research and its developing level at home and abroadhave been elaborated. Summarizing numerical methods of structural seismic responseanalysis and basing on seismic theory, analytical mode of soil-structure interactionsystem is determined. The constitutive models of soils and structure material aredetermined and damage limit is introduced in reinforced concrete material model. TheMat_Concrete_Damage model and erosion technique which incorporate most of concretedynamic characteristics such as strain rate effect, damage accumulation, fracture failure,etc., are suitable to simulate the damage state of reinforced concrete under earthquake.And the precise parameters are obtained based on the test results of other researchersthrough reading related references.The finite element analysis solution is modified for the soil-structure dynamic interactionsystem. Three-dimensional dynamic finite element analysis model of frame structures on rigidfoundation and soil-structure interaction system are established by selecting the type of the finiteelement, the means of input of the earthquake wave and the gravity load of system. Thesimulation analysis of frame structural’s crack distribution and failure state is similar to the testresults of vibration table. It shows that the LS-DYNA software is viable to study the damage ofreinforced concrete frame structures. Based on comparative analysis of the process fromdeformation, crack until collapse on rigid foundation and considering soil-structure interaction,the main conclusions are obtained as follows:(1) The variation tendency of floor peak acceleration of five layer, ten layer and fifteenlayer frame structures on rigid foundation are similar. The top peak acceleration increases with the increase of structure stiffness. The more the number of layer, the greater the amplificationfactor of top peak acceleration to the ground acceleration.(2) The first breakdown point of frame on rigid foundation appears later with increase ofstructure stiffness. The more the number of layer, the earlier the first breakdown point of frameappears. The first breakdown point of five layer frame appears at beam bottom and post edge ofbottom edge framework, while that of ten and fifteen layer frames appear at the upper floor offrame. The reason is the influence of the structure of high vibration mode.(3) Natural frequency of vibration of soil-structure dynamic interaction system is lower thanthat of frame on rigid foundation, and which on hard soil is higher than on soft soil. The floorpeak acceleration is more even than that on rigid foundation. The floor peak acceleration is lesserthan which on rigid foundation at most frames, but reduction coefficients are greater than1atindividual floors of ten and fifteen layer frames. It indicates that structure seismic design basedon rigid foundation assumption is not always safe.(4) The first breakdown point of frame considering soil-structure dynamic interactionappears later than which on rigid foundation. The first breakdown point of frame on hard soilappears earlier than which on soft soil. It means that the effect of soil-structure dynamicinteraction on soft soil is more obvious. The first breakdown point of frame appears at beambottom and post edge of bottom framework considering soil-structure dynamic interaction. It isdifferent from frame on rigid foundation. And the cracks of superstructure are lesser than whichon rigid foundation. The whole settlement occurred in soil-structure dynamic interaction system,and the settlement in soft soil foundation is more serious than which in hard soil.(5) That beam and column on each layer of the model structures are destroyed alternately ismixed collapse mechanism. Damage of the lower floors is more serious, that is mainly due to thelower floors bear a relatively large gravity load. The damage range at the bottom of the structureexpands gradually when the rigidity of structure increases. The reason is that damage of thelower floors occurs earlier when rigidity of structure is low and seismic energy is consumed toreduce the affect of earthquake to the upper structure.