Analysis and modelling of the seismic behaviour of high ... - Ingegneria

3.1 Introduction
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3 SEISMIC BEHAVIOUR OF BOLTED END PLATE
BEAM-TO-COLUMN STEEL JOINTS
In high seismic risk areas such as California and Japan, steel-framed buildings
have frequently been employed because of their excellent performances in terms
of strength and ductility. Nevertheless, a large number of entirely unexpected
severe brittle cracks of welded beam-to-column connections were found in the
recent Northridge (1994) and Kobe (1995) earthquakes (Bertero et al., 1994,
Kuwamura, 1998). The failures raised many questions regarding the validity of
design and construction procedures used for these connections at the time. Since
the earthquake, several extensive analytical and experimental studies have been
conducted to investigate the various aspects believed to be associated with the
failure observed in the pre-Northridge connection and to improve connection
performance. The majority of the thorough investigations established that
premature cracking in welded steel connections resulted from a combination of
factors, such as high strain demands coupled with large inherent flaws and stress
risers, overreliance on low-toughness materials, deficient field welding and
insufficient quality control.
As a result of poor performance of flange-welded moment connections, end plate
moment connections may represent, especially in Europe, an alternative to welding
in seismic regions. But because of limited cyclic testing of moment end plate
connections, extensive research has been initiated. In the framework of a research
programme conducted by the Department of Mechanical and Structural
Engineering of the University of Trento and sponsored by a MIUR-PRIN project
devoted to the analysis of semi-rigid beam-to-column connections, the presented
study has a two-fold purpose: