Simulation Analysis Of Construction Process Of Seismic-isolation Retrofit With Hoop-type Underpinning Joints

Due to seismic-isolation retrofit with hoop-type underpinning joints,the constraints of the structure changes during the construction process.At the same time,due to the special structural requirements of the scheme,the construction needs to be carried out in batches and sections.Therefore,the differences of the construction steps and the jacking machine control mechanisms will affect the structure.If set up or controlled improperly,it may cause damage to the original structure,even cause the collapse of the superstructure and affect the safety of seismic-isolation retrofit.Thus,it is necessary to control the construction process of seismic-isolation retrofit with hoop-type underpinning joints to ensure construction safety.In this paper,finite element method is adopted to simulate the construction process of the seismic-isolation retrofit the existed frame building with the hoop-type underpinning joints.The following studies are mainly carried out:1.Stage construction is used to simulate the construction process of seismicisolation retrofit.Both the construction steps and the jacking machine con trol mechanisms are discussed to affect the internal force and the deformation of the structure.The results show that the axial force of column and the internal force of beam will change greatly compared with the original structure when jacked up and load ed into the construction steps of installing isolation bearings.The lifting target loading value of each column should be determined by simulation analysis of construction process.When jacking up and removing columns,we should pay attention to monitoring the displacement at the end of columns to prevent the isolation bearing from being pulled.The lifting and unloading of each column should be carried out as synchronously as possible,and the allowable displacement difference should be less than L/800.2.Based on the characteristics that the hoop-type underpinning joint can be constructed in sections,the variation law of internal force and deformation of the structure under different construction sections is analyzed.The results show that the effect of subsection construction is only on the components in the construction section and the directly connected components,but not on the other components.Only the internal force of the cross beam in the reinforced members will be obviously affected by the follow-up construction section.The completed construction section will affect the remaining unreinforced members under the redistribution of internal forces.It is necessary to adjust the lifting stage of the remaining structure to avoid the excessive residual axial force affecting the construction safety.3.Analyse the change rule of internal force and deformation in different construction sequence.The results show that different construction sequence will lead to different forms of internal force redistribution.The earlier the components are constructed,the greater the difference between internal force and final state.The scheme 1 has the least influence on the redistribution of internal forces.4.The vertical progressive collapse analysis and robustness analys is of the structure during the construction of seismic-isolation retrofit are carried out by using alternate method and pushdown analysis method.The results show that the structure still has anti-collapse ability after the failure of the hoop-type underpinning joints.In the process of isolation and reinforcement,when the column is truncated and the isolation bearing is not installed,the structure is most likely to collapse.And the importance of the components that cause the overall failure of the struc ture is in turn corner column,short side column,long side column and middle column.