Study On Preventing Damage Of Multi-layer RC Frame Column Under Earthquake

It has been required that multi-layer concrete frame structure must reach a result as “strong column-weak beam” under seismic action in Chinese seismic code.However,according to several studies of frame structures destroyed in earthquake in recent years,we can figure out that most of multi-layer concrete frame structures tend to be destroyed in the bottom column.Most of the structural bottom pillars were severely destroyed or even collapsed in upper or lower ends,but the upper structures were relatively unbroken.The strong column-weak beam yielding mechanism can be affected by many factors,such as the influence of the in-filled walls on the stiffness of the bottom layer,or the strengthening of the beam stiffness by the actual reinforcement.In this paper,combined with engineering examples,the seismic behavior of the multi-layer concrete frame structure under the frequent earthquake and the rare earthquake is studied.By analyzing and comparing the story drift,base shear force,floor acceleration and plastic hinge in the three cases of setting foundation beam,bottom frame beam and bottom frame beam with flange plate on the upper part of multi-layer concrete frame foundation,the optimal seismic measure to improve the seismic capacity of the bottom frame column of RC structure is obtained.The main research contents are as follows:Firstly,multiple models are created by basing on the three conditions.Secondly,it conducts frequent earthquake researches on several models that have been established.By comparing and analyzing the maximum story drift of the structure,it is concluded that the seismic performance of the structure and bottom column are improved when the frame beam is set on the upper part of the foundation.At the same time,when the flange plate is 5×120mm,the structure has the minimum story drift and the bottom column has the best seismic performance.Finally,rare earthquake analysis are performed on several models that have been established.The nonlinear time-history method is used to compare and analyze the plastic hinge,base shear forces,floor acceleration and story drift of the structure under three seismic waves.It is found that when the foundation beam is placed on the upper part of the foundation,the plastic hinge first appears at both ends of the bottom frame column.when the frame beam is placed on the upper part of the foundation,the plastic hinge first appears at both ends of the beam.when the flange plate is 5×120mm,the time of the appearance of bottom column plastic hinge was deferred,and the story drift is decreased,the substrate shear force and floor acceleration are increased.In order to ensure the rationality of the conclusions,the results are applied to the three-layer and five-layer concrete frame structures for the multi-layer concrete frame structure.The conclusions are obtained by analyzing the rare earthquakes of the threeand five-story concrete frame structures.Using the same seismic measures,the storydrift,the base shear forces,the floor acceleration and the plastic hinge of the three-layer and five-layer structures under three seismic waves are studied,and the conclusions obtained are consistent with the four-layer concrete frame structure.Through the study of the various situations above,it is concluded that when the frame beam is placed at the bottom of the multi-layer concrete frame and the flange plate is 5×120mm,the bottom column has the best seismic performance.In this paper,the seismic behavior of multi-story concrete frame structures under the action of frequent and rare earthquakes is studied respectively.The measures to effectively improve the seismic performance of structures and the mechanism of“strong beams-weak columns” are obtained,which can be used as reference in practical structural design.