High strength tubular columns and connections under earthquake, fire loading and fatigue

  • G. Zanon
  • A. Kumar
  • O. S. Bursi
  • F. Ferrario
  • A. Giacobbe


High strength steel (HSS) has been available for many years. However, its use in onshore engineering
is quite restrictive. Nonetheless very recently, there was a growing trend for the use of HSS in tubular
structures thanks to Eurocode 3 Part 1-12 (2006) that extended its scope to steel grades up to
S690/S700MC. Nonetheless, Eurocode 3 Part 1-12 imposes many limitations at thematerial, structural
and design level. The ambitious targets of two EU funded –ATTEL and HITUBES – projects are to
increase the performance of tubular structures, reduce weights, construction and operating costs by
change in conceptual design and implementation of HSS. In a greater detail, the intent of the ATTEL
project, is to promote the use of HSS members endowed with circular hollow sections in buildings subject
to earthquake and fire, in order to understand the actual behaviour of HSS material and to show the possible
benefits with respect to mild steel. The buildings were realized with TS590 for steel columns and S275 for
beams in order to satisfy the capacity design criterion for columns and beams under earthquake
loading. The preliminary design of these structures leaned towards two fundamental conclusions: i) the cost
benefits related to the use of HSS columns in braced frames, which are mainly subjected to axial
loads and low bending moments; ii) the cost benefits related to the use of HHS columns in unbraced frames
only achieved along the main direction and for "medium" earthquake loading (<0.25g). Physical tests
both on full scale beam-to-column joints and column base joints to be performed at the University of Trento
will allow details for these important components to be checked. As far as the HITUBES project is concerned,
the main work regards members and joints subject to monotonic, low-cycle and high-cycle fatigue loading.
In particular, the project is focusing on: i) extraction of tubular welded and bolted joints from two case
studies, i.e. a footbridge and a railway bridge, respectively; ii) definition of weld condition –overmatching and
undermatching – electrode selection and post-weld treatment –peening- for welded tubular joints.