Study On The Reinforcement Of Isolation Pier With Independent Column Type Based On The Optimal Reinforced Rate

In the isolation building,the isolation pier,concrete column,is used to support the laminated rubber bearings.At present,the seismic isolation pier is regarded as a cantilever column in the actual project,and the eccentric compression member theory is used to design the reinforcement.In fact,the isolation piers are usually larger in size and lower in height due to the requirements for the installation of the seismic isolation bearings and the dynamic stability requirements during large earthquakes,and are more similar to piers than columns.At the same time,the isolated piers are subjected to shearing force,axial force and bending moment,and the bending moment is coupled with axial force and shearing force.However,the calculation theory of eccentric compression members only considers the influence of axial force,and does not consider the influence of shearing force.Therefore,there is a difference between the reinforcement of isolated piers calculated by engineering and the actual stresses of the piers,and no detailed research and experiments have been carried out to verify them.In view of the above problems,the main research contents of this paper are as follows:(1)The finite element simulation analysis of the isolated piers with different geometrical dimensions are carried out under the external load,to make sure that the longitudinal reinforcement does not yield damage and fully utilized,Change the reinforcement area of the longitudinal reinforcement so that the stress of the reinforcement is roughly the tensile design strength,and the ratio of the area of the unilateral longitudinal reinforcement on one side to the cross-sectional area of the isolation pier is defined as the optimal reinforcement ratio of the isolation pier.Through the finite element simulation analysis of various isolation piers with different cross-section dimensions and different external loads,the variation law of optimal reinforcement ratio of isolation piers is summarized;(2)In order to facilitate the application of engineering personnel,it is necessary to give a reasonable formula of the optimal reinforcement ratio of the isolation pier,but since the finite element analysis results are related to many factors,direct fitting is difficult.Therefore,the topological optimization of the isolation piers under different loads and different loads is carried out,and the force skeleton of the isolation pier is obtained,then the simplified force analysis model of the isolation pier is established.By using the simplified force analysis model,the Correlation between the optimal reinforcement ratio of the pier and the external load and the geometry of the buttress is obtained;(3)1Based on the established correlation,the formula of the optimal reinforcement ratio of the isolation pier is formulated.Under different stress states,the isolation piers will have two types of failure modes: longitudinal yield failure and concrete compression failure.According to the two different stress characteristics,this paper defines the isolation pier to be tensioned and compressed respectively,and the corresponding reinforcement calculation formula is fitted.The above studies lead to the following conclusions:(1)When the shear deformation of the isolation bearing is less than 200%,regardless of the axial force and the geometric parameters of the buttress,the reinforcement ratio of the isolation pier support can meet the requirements according to the structural reinforcement ratio of the frame column.When the shear deformation of the isolation bearing is greater than 200%,it is necessary to carry out the reinforcement according to the actual force of the isolation pier,and the optimal reinforcement ratio increases with the axial force,first decreases to the minimum and then increases;(2)There is a large tensile stress on the steel bars on the forced side of the isolated pier,the isolated pier is prone to tensile failure which is defined as isolation pier tensioned in this paper and the optimal reinforcement ratio is controlled by the tensile stress of the tensile reinforcement.With the increase of axial force,the bending resistance of the section of the pier is increased,and the isolation pier is transformed from the tensile failure to the compression on the other side.The maximum stress of the reinforcement occurs on the pressure side,and the reinforcement area of the isolation pier is controlled by the stress of the stressed side steel bar;(3)According to the finite element simulation results,combined with the simplified force analysis model of topology optimization,the reinforcement formula of the isolation pier is obtained,and the fitting formula is compared with the finite element simulation result.The ratio between fitting formula calculation and finite element simulation results is in the range of 0.85-1.25 which illustrate that the formula for the reinforcement of the piers given in this paper is reasonable.