Optimization Analysis Of Semi-rigid Joint Of Fabricated Concrete Frame Structure

Prefabricated concrete frame structure is one of the common prefabricated structural forms,and the seismic performance of the frame structure is partly determined by the performance of joint.This paper is based on a new type of stiffnesscontrollable fabricated joint.Numerical simulation and stiffness optimization analysis are carried out in order to obtain the best performance optimization method of this joint.In addition,the post-earth vulnerability analysis based on the IDA method is used on the cast-in-situ and semi-rigid structures.Two shock sequences situations are considered: one is only main shock sequence and the other is mainshock-aftershock sequences.In this way,the performance and application advantages of the new semirigid nodes can be verified,with a view to the subsequent actual Production and application provide a theoretical basis.The new joints studied in this paper are subjected to bending moments on the upper and lower steel plates and shear forces on the middle pin bolt connections.The stiffness of the joints can be controlled by changing the thickness of the connected steel plates to optimize the seismic performance of the structure.Open Sees finite element analysis software is chosen to simulate the joint performance of such joints and finally the numerical simulation rationality and the related calculation of the seismic performance of the structure for optimization analysis are carried out.The main research contents are as follows:(1)Analysis on the structure as well as the force principle of this new type of controllable stiffness joints,advantages and the corresponding pseudo-static test schemes and results are studied.(2)Numerical simulation at the node level was carried out and the thickness interval of connected steel plates was determined.Two kinds of models were set up by using Open Sees: the refined modeling method was used to optimize the thickness interval of the joint while the simplified modeling method was used to do the seismic analysis of the whole structure.At the same time,the feasibility of both modeling methods were verified by fitting and analyzing with test data.Finally,the optimal thickness of steel plate could be determined through changing it by gradient.(3)Numerical simulation at the structural level was carried out to verify that the new type of joint meets the requirements of seismic codes and has seismic advantages.A five-story and a ten-story cast-in-situ and semi-rigid reinforced concrete frame structures were built by Open Sees.The maximum inter-story displacement angle was chosen as the post-seismic index,then the post-seismic results of structures under the action of small,moderate,and large earthquakes were compared to analyze the different trend and post-seismic results thus the superior performance of semi-rigid joints was verified and the optimal steel plate thickness could be determined under each specific cases.(4)Vulnerability analysis of reinforced concrete structures under consideration of main earthquake was carried out.The influence of the use of semi-rigid nodes on the probability of the structure was studied in each different certain l IMit state under the action of earthquakes.Five-and ten-story reinforced concrete frame structures were established by Open Sees,and then the seismic vulnerability analysis was performed.Finally,the simulation results were compared with the test result.It can be found that the probability of failure of the semi-rigid structure is lower than that of the cast-inplace structure,and with the increase of the ground motion effect,the vulnerability curves of the two are obviously different,that is,the greater the ground motion effect,the better the seismic performance of the semi-rigid structure.The maximum difference in failure probability of cast-in-place and semi-rigid structures in IO,LS,and CP states is 3.27%,4.31% and 5.38% in five-story structures while which is 18.03%、25.47%和32.73% in ten-story structures.(5)The post-seismic performance analysis of the structure under the mainshock and aftershock was considered.Serious damage to the structure caused by aftershocks has been shown by existing studies,while the semi-rigid nodes studied in this paper are post-earthquake replaceable structures,that is,the damaged joints can be replaced after the main shock to restore the seismic performance of the structure.To verify the repairability characteristics of this semi-rigid structure compared with cast-in-situ structures under the consideration of the main and aftershocks,the comparison of the post-seismic performance of the cast-in-situ and semi-rigid structures under the main and aftershocks was discussed.The results show that the semi-rigid structures under the main and aftershocks shows a greater seismic performance.The maximum difference in failure probability of the main and aftershocks cast-in-place and aftershock semirigid structures in the IO,LS,and CP states are 9.71%,20.82%,and 32.73% in the fivestory structure while which is 23.93%,34.51% and 44.57% in the ten-story structure.