| In previous earthquakes,it was repeatedly found that the reinforced concrete frame structure did not exhibit the expected "strong column and weak beam" damage mechanism,and the structure produced a large residual deformation or even serious collapse,resulting in significant personnel and property losses,increasing the repair cost and difficulty after the earthquake;At the same time,after the Wenchuan earthquake,China timely revised the seismic standards and codes such as “Code for Seismic Design of Buildings”,“Standards for Seismic Assessment of Buildings” and “Technical Regulations for Seismic Strengthening of Buildings”.Therefore,a large number of frame structures designed according to the old norms can not meet the needs of China's economic development level,nor can it meet the requirements of new codes and standards,so need to improve the seismic capacity of existing frame structures.Preearthquake preventive seismic strengthening is a cost-effective measure to improve structural seismic performance and meet the requirements of the new regulations.At present,there are two major problems in the seismic strengthening technology of RC frame structure in China.One is the indoor reinforcement method,and the other is the reinforcement scheme that stays at the component level.In view of the above,this paper proposes an externally attached segmented variable stiffness BRB braced steel frame-frame structure reinforcement scheme.The use of external substructure reinforcement method can effectively avoid a series of disadvantages of indoor reinforcement.At the same time,BRB can form “integrated key components” due to its unique seismic energy dissipation characteristics.In addition,to avoid the occurrence of weak layers at the bottom of the frame structure,adopts a variable stiffness design along the height of the layer.In order to understand the seismic collapse performance of this seismic strengthening scheme,a three-dimensional finite element model before and after reinforcement of a six-story reinforced concrete frame structure was established,and elastoplastic time history analysis,Pushover analysis and incremental dynamic time history analysis were carried out.The seismic performance of the RC frame structure before and after the reinforcement of the segmented variable stiffness BRB braced steel frame is presented.The work done in this paper and the conclusions obtained are as follows:1.The externally segmented variable stiffness BRB-supported steel frame-frame structure is designed based on the stiffness requirement.The finite element model of the RC frame structure before and after reinforcement is established by SAP2000 software,and the modal analysis and mode response spectrum analysis are carried out.The analysis results show that the seismic action and interlaminar shear force of the structure after reinforcement are increased,but the interlaminar shear force and interlayer displacement angle assumed by the original frame structure are significantly reduced,and the displacement angle distribution between the layers is more uniform.The anti-seismic reinforcement external structure has a good protection effect on the original structure,and the seismic strengthening effect is obvious.2.According to China's seismic code,three natural waves and one artificial wave are selected,and the peak value of the seismic wave is uniformly adjusted to 400 gal.According to the ratio of 1:0.85,the two main directions are input along the structure,and the absolute maximum lateral displacement and maximum layer of the floor are obtained.The displacement angle,the plastic hinge distribution and the hysteretic energy of the BRB support.The analysis results show that the externally segmented variable stiffness BRB-supported steel frame plays a role in controlling the deformation of the overall frame structure—from the shear deformation mode to the overall deformation mode,so that the deformation of each floor tends to be uniform,and the structure is played.The overall seismic capacity,while the BRB support consumes considerable seismic energy,improves the energy consumption of the structure and reduces the seismic response.3.Based on the ability spectrum method,the finite element model before and after reinforcement is analyzed by the inverted triangle and the combined mode of lateral mode.The shear stress-vertex displacement curve of the structure and the performance point and plasticity under different seismic intensities are obtained.The case of hinge distribution.The analysis results show that the externally-segment variable stiffness BRB-supported steel frame improves the lateral bearing capacity of the existing frame structure and improves the yield mechanism of the existing frame structure—from the inter-layer yield mechanism to the overall yield mechanism.The ground avoids the concentration of interlayer deformation and improves the anti-collapse ability of the structure.4.10 seismic records were selected from the PEER ground motion record database,and 10 seismic records were sequentially subjected to dynamic time history analysis by gradually increasing the PGA method,and the IDA curve clusters of the two structures were obtained respectively,and the quantile was performed.Curve statistics,16%,50%,84% quantile curves were obtained to determine the limit state point of the 50% quantile curve.Based on the IDA curve data,the collapse rate vulnerability analysis was proposed to obtain the collapse rate of the structure.Curve to determine the structural collapse reserve coefficient CMR.It can be seen from the single IDA curve and the IDA curve cluster that the yield point and the non-collapse limit state point of the frame structure after reinforcement are obviously higher than the original frame structure,and the limit of the collapse bearing capacity is obviously increased.At the same time,the interlayer displacement angle is also fixed when collapsed.improve.From the performance point of the 50% quantile curve,the inter-layer displacement angle of the external segmented variable stiffness BRB-supported steel frame-frame structure corresponding to the corresponding limit state point of the original frame structure is increased by 6.25%,25.68%,and 115.67,respectively.%,25.48%,the corresponding peak acceleration increased by 86.76%,88.74%,118.09%,26.39%,respectively.From the analysis of the vulnerability curve,it is known that the external segmented variable stiffness BRB-supported steel frame structurestructure collapse reserve coefficient is 4.81 times that of the original frame structure,and the increase is obvious.After the reinforcement,the seismic performance of the frame structure is obviously improved,and the failure probability under each limit state is smaller than that of the original frame structure,and the overall collapse resistance of the structure is significantly improved. |
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