Seismic Behavior And Design Method Of The New Connections For Steel Frames

After Nortiridge and Kobe earthquake, it was found that the traditional beam-column jionts in steel frame happened brittle failure largely. Scholars at home and abroad had done many researchs about improving the beam-to-column connections after the earthquake. At present, the method of improving the jionts have reduced section beam connections and reinfored connections. This solution, despite being able to successfully concentrate plasticity and avioding brittle failure in jionts, presented difficulties in terms of the reparability of damaged parts of the structure. In order to achieve more efficient earthquake resisitant structures, an innovative fuse device for dissipative beam-to-column connections in seismic resistant steel frames was developed. The device consists on steel plates welded to the web and lower flange of the steel beam and steel cover. Damage was concentrated only within the devices, which proved to be easy to replace, with the remaining parts of the structure lying under the elastic range. Through the finite element analysis and theoretical analysis, the performance of the new jionts and structural forms are discussed, and putting forward the designed method of the new connections in this paper. What is more, theoretical formula were calibrated based on the the numerical models results, and to the discussion of the factors that influence its seismic performance. The detailed research contents are as fllows:(1) In view of the dissipative plates yielding ahead of the beam-to-column joints and the beam and column lying under the elastic range, the size of the dissipative plate was derived in the paper. To ensure the global stability of the fuse device, the inertia moment requires for the device was obtained based on the strength required for the steel cover. The contact force between the dissipative plate and the rectangular-shape cover are formulated to keep them from local buckling. In order to adapate to the structure form of the C-shape-cover connections, the gap between the dissipative plate and the C-shape cover is formulated.(2) A physical model will be created in nonlinear finite element software ABAQUS and its numerical analysis under the action of static loads. The research show that the theoretical derivation of the contact force between the dissipative plate and the rectangular-shape cover accord with the results of the finite element well. The new connections of three kinds of structure forms can achieve successfully that damage was concentrated only within the devices, which proved to be easy to replace, with the remaining parts of the structure lying under the elastic range. The bearing capacity of rectangular-shape cover jionts is optimal. The bearing capatity of the new connections with the increase of reinforced plate s thickness and the decrease of the free length and the increase of the rectangular-shape thickness increase. The smaller the gap is, the stronger the bearing capacity of the new jionts will be. If the gap is too small, the beam will occure plastic deformation.(3) A physical model will be created in nonlinear finite element software ABAQUS and its numerical analysis under the action of cyclic loads. The results show that the bearing capacity of rectangular-shape cover jionts is optimal. With the decrease of the ratio between dissipative plates s width and thickness and free length and the gap, the energy dissipation of new connectios have a tendency to incraese. At the same time, stiffness degradation has a tendency to slow down. The bigger the reinforced plate s thickness, the more the new connections dissipate energy. However, the thickness of reinforced plates has little impact on the stiffness degradation.