| With the development of building industrialization,steel structures,especially those using bolted connections to achieve fully prefabricated construction,have good application prospects.The high seismic performance and a practical design method are the prerequisites for the application and popularization of a new type of structural system.In this dissertation,the seismic behavior and the design method of steel frames with square steel tube columns,bolted end-plate joints and flexiable braces were studied.Firstly,a full-scale quasi-static test and an 1/3 scaled shaking table test were carried out to study the seismic performance of the frames.Secondly,finite element models were developted based on the implicit analysis in the software ABAQUS.Then,a practical design method was proposed and six groups of example frames were designed.Finally,seismic behavior of the example frames were studied and the reliability of the proposed design method was verified.The main research works of this dissertation are as follows.(1)A quasi-static test was conducted on a full-scale three-story specimen.Global behavior including failure mode,hysteresis behavior,loading capacity,stiffness,deformation performance and energy dissipation were discussed.Based on the deformations in joints and strains on the surfaces of members measured during the test,hysteresis behavior,backbone curves,loading capacity,ductility,component of story drift ratio and energy dissipation of the joints were studied,the loading performance of members were analysed,and the failure sequence as well as the plastic development procedure of different positions of the frames were summarized.(2)A shaking table test was conducted on a five-story 1:3 scaled model.The test phenomena,acceleration responses,deformation performance and failure mode of the frame were studied.The natural vibration period,frequency,mode and their variation trends under different damage conditions of the structure were discussed.The loading performance and plastic development of the members in the bottom two stories were analysed.(3)Refined finite element models with high simulation accuracy were established to simulate the cyclic performance of the steel frames with square steel tube columns,bolted end-plate joints and flexiable braces using solid elements,shell elements and truss elements.The complex contact status,the joint deformation and the local buckling of members could be simulated.Meanwhile,line-element models with appropriate accuracy were also established using beam elements and truss elements,which could be used for large-scale parametric study.(4)The seismic design methods in the structural design codes of China,Japan,America and Europe were reviewed.The simplified calculation methods of initial rotational stiffness and moment capacity of I-section beam to square steel tube column joints were supplemented and studied.The definition of the stiffness ratio of brace to frame was proposed.Then,a practical seismic design method was proposed for the steel frames with square steel tube columns,bolted end-plate joints and flexiable braces.Six groups of example frames with different parameters,including the number of stories,steel strength,and the stiffness ratio of brace to frame,were designed using the proposed method.The influence of the stiffness ratio of brace to frame on the main design parameters was discussed.(5)Static pushover analysis and dynamic time history analysis were carried out to study the seismic performance of example frames,including loading capacity,deformation,ductility coefficient and over-strength coefficient.Study on the influence of the stiffness ratio of brace to frame on the structural seismic performance was carried out,and the recommended value of the stiffness ratio of brace to frame was put forward.The effect of high strain rate caused by sudden tensioning of braces under seismic load on the overstrength of braces was studied,and the load adjustment coefficient of brace joint design was suggested. |
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