ABSTRACT
Full scale specimens of welded X-joints, of traditional and bird-beak configurations, were tested under inelastic cyclic loading to assess their seismic behaviour. The results showed that local failure of the joints occurred before any significant plastic deformation of the chord was observed. The traditional joints experienced a punching failure of the braces into the chord and the bird-beak joints experienced lozenging of the chord and fracture along the chord corner with less punching failure. Energy dissipation, ductility ratio and strength resistance ratio were used to assess the seismic toughness of the joints. It was concluded that bird-beak joints gave a better performance than traditional joints, but care must be taken in drawing general conclusions as this study only involved limited full-scale tests of each type of joint. A metallurgical study suggested that the cause of the fractures was ductile crack initiation due to low cycle fatigue, although crack propagation has, in some cases, resulted in final brittle fracture.
