European pre-qualified steel joints

Nowadays, prequalification criteria for steel beam-to-column joints in seismic resistant systems are currently missing in Europe. Even though several experimental and analytical studies are available, none was specifically addressed to select and prequalify European seismic-resistant joints on the basis of parametric experimental and numerical investigations. At the current stage, EN 1998-1 allows using dissipative beam-to-column connection, but it prescribes design supported by experimental testing, which results in impractical solutions within the time and budget constraints of real-life projects. On the other hand, no design tools to reliable predict the plastic rotation capacity of non-dissipative (namely full strength) joints are available. Indeed, owing to the variability of steel strength, these connections could not have enough overstrength (e.g. min 1.1×1.25 Mb.rd, being Mb.rd the bending strength of the beam), and in such cases their plastic rotation capacity must be prequalified by relevant test and numerically based procedures. In contrast to current European design methodology, the approach used in other countries with high seismic hazard (e.g. USA and Japan) is based on codified and easy-to-use design tools and procedures and prequalified seismic resistant joints are common practice. After the Northridge earthquake, the US research effort was addressed to prequalify a set of selected joint types to be used in both special and intermediate moment resisting frames. Since 1995, US FEMA and SAC joint venture developed a six-years research project (the FEMA/SAC program) devoted to provide guidelines for seismic design of steel moment resisting steel frames, including codified criteria for inspection, evaluation, repair, rehabilitation, and construction of steel moment frame resisting structures. The results arisen within the FEMA/SAC program were directed to feed into a specific standard (ANSI/AISC 358-05) containing design, detailing, fabrication and quality criteria for the set of prequalified typologies, which includes the most common configurations of joints used in the US practice, e.g. welded-flange-bolted-web connections, haunched and cover-plated connections, bolted T-stub connections, and double-flange-angle connections. Seismic prequalification activity was also successfully accomplished in Japan, were columns are usually made of cold formed steel tubes with shop weld placed at a short distance away from the face of the column. Unfortunately, joint typologies and shape and properties of members, bolts and welds commonly used in US and Japanese practices, are different from those typically used in Europe. Moreover, it should be noted that the European seismic input differs from US earthquake, also affecting the ductility demand at both global and local level and thus furtherly limiting the application of US prequalification to the European practice. In the light of these considerations, “Equaljoints” project was aimed at providing European qualification of beam-to-column joints for seismic application, focusing on the standardization of design and manufacturing procedures with reference to a set of selected joint configurations, namely bolted haunched joints, bolted extended stiffened end-plate joint, bolted extended unstiffened end-plate joint and welded dog-bone joint, which were designed to provide different performance levels