Study On Shaking Table Test And Seismic Performance Of High Strength Steel Composite K-eccentrically Braced Frames

High-strength steel composite eccentrically braced frames（HSS-EBFs）have the advantages of both high-strength steel and eccentrically braced frames.The HSS-EBF structure dissipates energy through the plastic deformation of links during an earthquake,during which the beams and columns are still at the elastic stage or have entered the initial plastic stage,owing to the use of high-strength steel.Thus,high plastic deformation requirements for high-strength steel members are not required.HSS-EBFs make good use of the advantages of high-strength steel,which include high-strength,relatively smaller size（compared to ordinary steel）of its members under the same design load,light self-weight,low cost,and large net space.An in-depth study of the seismic performance and failure mode of HSS-EBFs is helpful in promoting the application of high-strength steel in the seismic fortification areas of china.To research seismic performance of HSS-EBFs,the following research work was carried out:（1）A shaking table test was conducted on a three-story high-strength steel composite K-eccentric braced frame specimen with a scale ratio of 1:2.The links used were of the shear yield type.The acceleration response,displacement response,and energy beam response of the specimen under different levels of earthquakes were measured.The story shear distribution and story drift were analyzed.The experimental study showed that the structure is in the elastic state under the action of a frequent8-degree earthquake,and the stiffness decreases slightly under the action of a rare8-degree earthquake.The maximum story drift angle under frequent and rare earthquakes is far less than the limit requirement of the seismic code.（2）Based on the shake table test of K-HSS-EBFs,dynamic elastic-plastic analyses were conducted to research the influence of the length of links,height-to-thickness ratio of link webs,depth-span ratio of structures,and brace arrangement to inelastic performance of K-HSS-EBFs.The results indicated that a different link length,link web ratio of height to thickness,and ratio of depth to span differently influenced the natural vibration period,story drift,distribution of floor shear force,load-carrying capacity of columns,brace shear force,and link rotation angle shear force.Some design recommendations were provided based on the analyses to provide a reference for engineering design.（3）Based on the performance-based seismic design method,four groups of K-EBFs were designed.Each group includes one conventional K-EBF and two K-HSS-EBFs.The story drift,rotation angle of the link,and story shear force of each group examples under rare 8-degree earthquakes were studied.The probability quantile curve and the fragile curve were obtained by adopting the method of incremental dynamic analysis.The seismic performance of conventional K-EBF and K-HSS-EBFs were evaluated using the story drift as the structural performance parameter.The probability of the story drift exceeding the specification limit was low under the action of frequent and rare earthquakes,which meet the limit requirement of seismic specification.With the structural frame beam column or brace yield as the limit state of K-HSS-EBFs,the maximum story drift,maximum link rotation angle and maximum horizontal seismic action that the structure could withstand were compared and analyzed.The studies showed that the deformation of the K-HSS-EBFs was larger than that of the conventional K-EBF under the same level of earthquake,and the higher the structure,the greater the deformation.In the limit state,the seismic action that the structure could withstand and the link rotation angle of the K-HSS-EBF made of Q690and Q345 were larger than that of conventional K-EBF.The elastic-plastic story drift of K-HSS-EBF made of with Q460 and Q345 was less than specification limit,while the elastic-plastic story drift of K-HSS-EBF made of Q460 and Q345 was larger than specification limit.Based on the analysis results,some design proposals were put forward.（4）The structural influence coefficient R,structural over-strength reduction coefficient R_?,and displacement amplification coefficient C_d were analyzed using the capacity spectrum method based on incremental dynamic analysis.It is worth noting that R increases with increasing steel grade,and tends to decrease as the number of stories increases;R_?and C_d exhibit no relationship trend with the steel grade,and tend to decrease as the number of stories increases.The relationship between R,R_Ω,C_d,and the structural steel strength and number of stories was studied.According to the research results,reasonable values of R,R_Ω,C_d were proposed,which could act as a reference for the strength-and performance-based seismic design of this type of structure.