Study on seismic behavior of steel frame joint with external arc diaphragm

The application of External Diaphragm (ED) in steel frame system is able to reinforce the stiffness of joint and provide efficient protection for the critical part of joint. However, due to the limitation of the existing design codes, the inside space of building is affected frequently by the excessive size of the ED. To reduce the size effect of ED, a hysteretic experiment on four steel joint specimens is first carried out in this paper, the effects of the width ratio (the ratio of ED width to beam flange width) and connection type (Bolted web-Welded flange (BW) connection and Full Bolted (FB) connection) are investigated. Then, a numerical analysis is conducted to further explore the influence of the width ratio and the thickness ratio (the ratio of ED thickness to beam flange thickness). The results indicate that the specimen with BW connection exhibits larger stiffness and bearing capacity, but the specimen with FB connection has obvious ascendancy on the ultimate deformation capacity and ductility. Moreover, Changing the width ratio and thickness ratio are unable to cause significant variation on the seismic performance of steel joint if the thickness ratio is larger than 1.25. Therefore, the thickness of the ED is more critical than width to the seismic performance of steel joint. Meanwhile, in the circumstance of the thickness ratio is equal to 1, the width ratio of 0.1 is recommended for the minimum limited value in structure design.