Finite Element Analysis On Seismic Performance Of Precast ULICC Plates Retrofitted Existing RC Frame Structures

In China,there are a large number of existing reinforced concrete(Reinforced Concrete,RC)frames,which cannot meet the seismic design requirements of the current codes.These buildings are either under service,which are not suitable for reconstruction,or historical protection buildings which cannot be demolished.Non-ductile damage may occur during strong earthquakes.Seismic reinforcement for existing RC buildings are required urgently.In addition,ignoring thermal insulation measures or low standard insulation design of those buildings cannot meet the requirements of green buildings advocated by the country.The low-carbon retrofit of such buildings also needs to be solved urgently.In order to study seismic performance of RC frame structure retrofitted with green insulation cementitious materials,FEM models were established based on the Ultra-lightweight Insulation Cementitious Composites(Ultra-Lightweight Insulated Cementitious Composites,ULICC)mixed in the previous test and the finished seismic experiment of RC frame retrofitted by precast insulation cementitious plates.Load transmission mechanism was researched by seismic performance of retrofitted RC frames considering different influence factors.Equations of lateral carrying capacity were proposed.The main contents of this paper are shown below :(1)ABAQUS was used for numerical simulation.The detail modeling process of RC frames with infills retrofitted by precast ULICC plates was introduced.Hysteretic curves,skeleton curves,characteristic values and failure patterns of FEM results were compared with previous test results.It is indicated that FEM results fit the test results well,which verified the correctness of FEM model.(2)The finite element models were established considering different influence parameters.Skeleton curve,stiffness degradation curve,characteristic values,energy dissipation and failure pattern of RC frames were systematically analyzed.The parameters such as reinforcement ratio,thickness of retrofitted plates,opening location,dimension of retrofitted plates,and material mechanical of ULICC were considered.The analysis results show that the lateral carrying capacity of the retrofitted RC frames increased with the increasing of reinforcement ratio,width and thickness of retrofitted plate,ULICC compressive strength.The bearing capacity decreased with the increasing of the opening area.The reinforcement ratio of the retrofitted plates performed less effect on the lateral carrying capacity.Total energy dissipation capacity increased with reinforcement ratio,width of retrofitted plate,ULICC compressive strength.RC frames with larger openings performed lower energy dissipation.Damage of structures was reflected by Mises charts.One-plate retrofit model performed higher strut effect compared to smaller width one.The high stress area and strut effect decreased with ULICC compressive strength decreased,which indicated that the increase of ULICC compressive strength led to more conducive of strut effect.Considering the results of parameter analysis,the reinforcement ratio and mixture of the retrofitted plates were not obvious to improve the seismic performance of the structure,while the opening rate,the number of retrofitted plates and the thickness of the plates were the sensitive parameters affecting the seismic performance of the retrofitted RC frame with infills.(3)Based on the FEM results,the stress of beam and column reinforcement considering different parameters was discussed.The result indicated that parameters influenced on yield order of reinforcement slightly except thickness and amount of retrofit plate.The shear distribution of the RC frame with infills retrofitted by precast ULICC plates during loading process was analyzed.The percentage of shear force undertaken by retrofitted infill decreased with the increase of story.The internal force redistribution between the retrofitted infill and columns was obvious during the loading process.The percentage of shear force undertaken by retrofitted infills increased with the increasing of reinforcement ratio,thickness of retrofitted plates and ULICC compressive strength.Under the same retrofit rate,the wider size of the retrofitted plates,the larger the percentage observed;the larger area of openings,the lower the effect of the retrofitted infills.The loading process can be divided into three stages.The load mechanism of each stage was analyzed.Based on the existing calculation formula,the carrying capacity of columns,the masonry infills and the retrofitted plates were added up by superposition method.The frame-retrofitted infills interaction coefficient was introduced.In order to ensure the universality of the calculation formula,the opening reduction coefficient was introduced.Calculation formula of the lateral carrying capacity of the RC frame structure retrofitted by precast ULICC plates under different influencing factors was proposed,which provides a reference for calculation of carrying capacity of the retrofitted RC frame structure with infills.