Super-high-strength steel with yield points of 800-1000N/mm2 is about to be used for building frames. A design method needs to be established that takes into account the poor welding performance as well as the larger elasticity of these materials. To this end, cruciform circular-column-to-beam connection specimens were tested and analyzed. Frame connection can be made by partial butt welding or super-high-strength bolts using an ordinal outer or ring diaphragm, and a horizontal beam haunch. Tests and analytical results confirmed that the elastic region extends further than that of a frame made of ordinary steel by about 1 % of story deflection angle. Initial stiffness, yield strength and maximum strength due to local beam buckling can be assessed by ordinary calculation methods. However, the slip and fracture strength of bolt joints using super-high-strength steel and bolts needs her investigation.
