Uncategorized

DESIGN AND ASSESSMENT OF STEEL STRUCTURES
IN SEISMIC AREAS: OUTCOMES OF THE LAST ITALIAN
CONFERENCE OF STEEL STRUCTURES

Elide Nastri

Department of Civil Engineering, University of Salerno, Fisciano (SA), Italy

Editorial

The use of steel for seismic resistant structures is a hot-topic of seismic engineering. During the last Italian Conference of Steel Structures – CTA 2017, held in Venice, the largest part of  the conference proceedings was focused on seismic issues regarding the design and evaluation of seismic performances in new buildings and the use of steel for the retrofit of existing buildings. The use of steel in seismic areas is not new as testified by many patents starting from the first decades of the Italian Kingdom [Cocco, 2018]. In fact, as it is known, steel construction in seismic areas provides many advantages as the weight reduction with a consequent reduction in seismic actions demand. In addition, steel members are usually able to develop wide and stable hysteresis loops under seismic loadings, thus affecting the global ductility of buildings [Mitsui et al., 2018]. For this reason, the need to accurately model the actual cyclic behaviour of steel member by means of simplified model becomes an urgent need. In particular, recent research efforts have been devoted to the modelling of degradation phenomena and pinching effects affecting the ultimate behaviour of dissipative zones and the overall seismic response of the structure [Giordano et al., 2017; Chisari et al., 2017]. In particular, moment resisting frames behavior under seismic loadings can be strongly affected by the degradation phenomena occurring in dissipative zones [Bernuzzi et al., 2018; Montuori et al., 2016a; Dell’Aglio et al., 2017; Ferraioli et al., 2016; Ferraioli et al. 2018a; Ferraioli et al., 2018b]. Moment Resisting Frames are usually cheaper than other steel typologies and assures an adequate seismic dissipation, provided that, connections are appropriately detailed and able to support the required strength and behaving as rigid connections [Tartaglia et al., 2018; D’Aniello et al., 2017; Tenchini et al., 2018; Pecce, 2016]. However, Moment Resisting Frames could not be used for high-rise buildings because of their high deformability for which braced frames or dual systems are preferred [Bosco et al., 2016; Faggiano et al., 2016; Costanzo et al., 2016; Montuori et al. 2016b; Montuori et al. 2016c; Montuori et al. 2017b; Costanzo et al. 2017; Costanzo et al., 2018; Mastrandrea et al., 2013]. In the last years, also cold formed profiles are getting head in the seismic field, used not only as a system for the strengthening and retrofitting of existing buildings [De Matteis et al., 2016; Castaldo et al., 2016; Totter et al., 2018; Formisano et al.; 2016] or for pallet racks [Gabbianelli et al., 2016] but also as the main structural system of new buildings, showing very small interstorey drift [Campiche et al. 2018] or as an innovative bracing system [De Matteis et al., 2018]. Other research fields regard the use of dissipative devices in place of traditional dissipative zones such as beam ends for moment resting frames or link for eccentrically braced frames [Lemos et al. 2018; Latour et al. 2018; Titirla et al., 2017; Fabbrocino et al., 2016]. The use of these devices, properly located in points where the high displacement demand is expected allow the structure to remain in service also after the seismic event and an adequate reparability, benefit the maintenance costs. From the other side, the use of base seismic isolation remains a useful strategy to limit the plastic excursion and, as a consequence, the structural damage [Avossa et al., 2017; Castaldo et al., 2016b]. The finish line is now the design and construction of buildings able not only to assure an adequate level of dissipation and reparability but also the chance to control the residual drift after both the single seismic event and seismic sequences.

$4.00Add to Cart

The seismic behaviour of moment resisting steel frames (MRFs) is strongly dependent on the plastic response of beams and columns. In this typology, it is common practice to foster the hysteresis in the beams ends and at the base of the columns of the first storey, thus relying on the resources of local ductility and energy dissipation capacity of the profiles. Therefore, in order to perform seismic non-linear analyses (pushover or time-history) mathematical models able to predict the inelastic response of the steel profile in terms of resistance and rotation capacity are usually needed. Currently, in technical literature, also due to the higher simplicity of the testing rigs, the available studies mainly regard the behavior of beams subjected to non-uniform bending, while the case of columns, which are subjected simultaneously to axial and bending loads, is frequently neglected.
Within this framework, in this paper an experimental and numerical work devoted to the monotonic behavior of square hollow sections (SHSs) (which are shapes frequently employed to realize columns) subjected to combined bending and axial loads, is presented. Results of experimental tests on steel profiles subjected to bending only or to simultaneous axial and bending loads are reported and, subsequently, with the aid of FE, a numerical analysis regarding about two thousand different cases is conducted to cope for variation of the influent parameters. The results of the experimental and FE studies are summarized in regression models expressing the ultimate resistance and rotational capacity of SHSs as a function of the main geometrical and mechanical parameters. The presented models represent a basic tool to run non-linear analysis of steel MRFs. Indeed, the maximum resistance of the member influences the redistribution of the actions in the structure, while the rotation capacity governs the local and global ductility of the structure. Both parameters are estimated properly accounting for the influence of non-dimensional axial load.

$2.00Add to Cart