| The steel structure is bestowed with unique advantages of light weight,high speed of construction,excellent seismic behavior and high degree of industrialization,which makes it one of the main forms of the prefabricated buildings.The bolted connections are the key to realize the prefabricated construction and embody semi-rigidity to some extent in practical engineering.By combining the semi-rigid steel frame and the braces,the concentrically braced steel frame with semi-rigid connections can be developed.It is a prefabricated building structure with dual lateral force resisting system,also a structural system with integration of seismic and damping.The semi-rigid connections can improve the structure's deformability and energy dissipation capacity,while the concentric braces can provide lateral stiffness to the frame,which makes the structure has broad application prospects in the future.In this paper,the seismic behavior of the structure was studied by experimental study,numerical simulation and theoretical analysis.The main research works and results are as follows:(1)The low-cycle reversed loading tests on the concentrically braced steel frame with semi-rigid connections were conducted.Three semi-rigid connections,namely the top-and-seat angle connection with web's ear plate,extended end-plate connection,T-stub connection,and two concentrical braces,namely chevron and cross brace,were chosen.Six specimens were designed and tested until failure under the low-cycle reversed loading to study the strength,ductility,stiffness degradation performance,energy dissipation capacity and failure mode in detail,and the seismic behavior of each specimen was compared.The results showed that the concentrically braced steel frame with semi-rigid connections has excellent seismic behavior.The braces cooperated well with semi-rigid steel frame in resisting the lateral loading,the structure has two seismic fortification lines.The structure had better strength and ductility when using extended end-plate connection.The structure showed more reasonable plastic development sequence and possessed better bearing capacity,energy dissipation capacity and ductility.(2)The finite element analysis of the semi-rigid connections and specimens was carried out.The finite element models of the top-and-seat angle connection with web's ear plate,extended end-plate connection and T-stub connection were established and their seismic behavior was studied.The finite element models of the specimens were established by ABAQUS and SAP2000,respectively,and the results of the finite element analysis were compared with the test results,which showed the results of the finite element analysis were essentially consistent with the test results,which proves the finite element analysis is feasible and effective.The analysis results showed that the seismic behavior of the extended end-plate connection was better than that of the others.The hysteretic performance,bbearing capacity,energy dissipation capacity and ductility of the chevron braced steel frame were better than that of the cross braced steel frame.(3)The cooperative working mechanism of the braced frame and semi-rigid steel frames was analyzed.Based on the simplified mechanical model,the lateral stiffness calculation formula of the concentrically braced steel frame with semi-rigid connections was deduced.Twelve analysis models were designed and then the elastoplastic time-history analysis under rare earthquake was conducted to calculate the best lateral stiffness ratio of the structure.Then the pushover analysis was carried out on the model with the best lateral stiffness ratio to study the overall lateral resistance performance of the structure.The cooperative working mechanism between the braced frame and the semi-rigid steel frame was clarified.The results showed that the maximum inter-story displacement angle reached its minimum and the energy dissipation ratio of the braced frame reached its maximum when the lateral stiffness ratio was 3.The braced frame entered the plastic stage earlier than the semi-rigid steel frame.When the braces buckled under compression,the bearing capacity of the braced frame reached its maximum,while the semi-rigid steel frame was still in the elastic stage,which comforted to the seismic design concept of the braces being the first seismic fortification line.(4)Based on the intergrated model,the seismic behavior of the concentrically braced steel frame with semi-rigid connections under different seismic fortification intensity was studied.Analysis models of the structure under different seismic fortification intensities and heights were established.The response spectrum analysis under frequent earthquakes and dynamic elastic-plastic time-history analysis under rare earthquakes were accomplished.Some seismic behavior indexes,such as maximum inter-story displacement angle,the development of plastic hinges and the shear distribution,were studied in detail.The results showed that the maximum inter-story displacement angle could meet the Code's requirements under the frequent earthquake and rare earthquake.The plastic hinge didn't appear on the column base and the structure showed excellent bearing capacity under the rare earthquake of seismic fortification intensity of 8 degrees(0.20g)and below.However,the plastic hinges appeared on the column base successively and the structure was not suitable to bear under the rare earthquake of seismic fortification intensity of 8 degrees(0.30g)and above. |
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