Seismic Damage Analysis Of RC Base Isolation Frame With Construction Joint And Experimental Study

The construction joint is an unavoidable problem in the reinforced concrete structure.Although there is no general“seam”on the macro scale,the discontinuity of material performance,the two stage concrete placement becomes the weak part of concrete structure at the joint.At present,many researches only aim at the research level of test blocks or components under the static condition.The research direction of its influence degree and influence scope on structure is very limited,especially for the research of isolation structure.Due to the lack of the analysis of the influence degree of the construction joints on the whole structure and the theoretical support of the system,in many cases,the influence of the construction joints is not considered when designing,generally considered as cast-in-place.This is not in line with the actual situation,especially in the case of earthquake dynamics.(1)The pseudo static test on the seismic performance of reinforced concrete columns with construction joints is studied in this paper.The test shows that the cohesive property of the concrete at the interface of the construction gap is poor,and the crack is caused by the load,and the width of the crack is larger in the later period.Through the analysis of the force mechanism of the construction joints,the numerical model of the construction joints is established.The axial compression ratio has a great influence on the construction joint,and the horizontal maximum bearing capacity of the construction joint column and the cast in place column decreases with the reduction of the axial compression ratio.The horizontal bearing capacity of the construction joint column under the same axial compression ratio is less than that of the whole cast column,and the ductility is greater than that of the whole cast column.(2)Secondly,a comparative model is established to study the setting up of the construction joints when the upper structure is provided with construction joints.In the column bottom and top frame for the establishment of construction joints,in addition to the mid span bottom damage,damage along the two ends of the beam top surface extending along the column direction,cause a certain degree of column damage.Under the rare earthquake,the safety coefficient of the anti overturning safety after the construction joint is reduced,which has a negative effect on the overturning of the structure.(3)Lastly,in order to set up the horizontal construction seam in the construction process for the foundation isolation structure of a university experiment building in the construction process,a multi scale model of the base isolation RC frame structure withconstruction seams under the seismic isolation layer is established.After the construction joint is set up under the seismic isolation structure,the bonding interface between the construction joints of the earthquake action is slipping,the friction energy of the new and old concrete interface and the local yield of the reinforcement are partially yielded in advance.Therefore,to a certain extent,the effect of the earthquake on the superstructure is slowed down to a certain extent,and it is beneficial to the earthquake resistance of the structure.However,the structural damage of the structure first begins with the position of the construction joint.The energy consumption of the joint surface of the construction seam is large and the rigidity of the lower buttress is low,which means that it enters the damage state in advance and concentrates on the local position of the construction joint,which causes the local concrete to be cut out and the steel bars yield in advance.The analysis of this paper shows that the force transmission between the construction joints is realized by the friction between the concrete and the pin bolt effect of the reinforcement.The interface between the construction joints and the reinforcement will consume part of the energy under cyclic loading such as earthquake.To a certain extent,it will play a positive role in reducing the response of the structure.But at the same time,the local energy consumption will lead to the position of the construction joint may enter the stage of plastic damage in advance.If the seismic input intensity is large and the holding time is longer,it may cause plastic hinge of beam column joints,resulting in failure of local components or continuous collapse of structures.