This paper presents three full-scale tests of beam-to-RHS column connections without weld access holes. The aim of the tests is to investigate the plastic deformation capacity and ultimate strength of this type of beam-to-column connection. The ultimate moment capacities of the welded beam to column joints were found to be predicated by simple formulas based on elementary plastic analysis. In all the specimens, the joints had sufficient overstrength to allow formation of plastic hinges at beam ends, although One Specimen failed by brittle fracture starting from the toe of welded joints between the beam flange and horizontal haunch.
The 1994 Northridge and 1995 Hyogoken Nanbu (Kobe) Earthquakes both took structural engineering professionals by surprise in that many of the welded connections in modem steel building frames sustained brittle fractures. A common practice for engineers before these earthquakes was to assume that the joints between the beam flanges and columns using complete joint penetration, (CJP) groove welds satisfy overstrength criteria to allow formation of plastic hinges in beams (CEN 1994, ICBO 1994). These fractures most frequently occurred in regions around the beam bottom flanges groove welds, in Northridge, brittle fractures initiated at a very low level of plastic demand, and in some cases, while structures remained nearly elastic, in Kobe, however, the majority of RHS column-to-beam connections that fractured during the Earthquake accompanied extensive yielding or local buckling at beam ends. This may suggest that small or moderate-scale reinforcements of beam-to-column joints would suffice for the joints to avoid tensile thilure and show sufficient rotation capacity. It was found that one important ca.~ for brittle fracture is stress and strain concentrations due to the existence of the weld access holes at beam-to-RHS column joints after the earthquake. Therefore the specimens proposed in this study had no weld access hole.
