PSI - Issue 44

Federico Gusella et al. / Procedia Structural Integrity 44 (2023) 790–797 F. Gusella et al./ Structural Integrity Procedia 00 (2022) 000 – 000

791

2

walls in and Macillo et al. (2014) and Fiorino et al. (2016 and 2018), checking the bolts to be characterized by over strengthen (Zampieri et al. 2019). The investigated bracing system (Fig. 1) has a transverse beam that behaves like a fuse. The long diagonal is a truss under tension and compression, which remains in the elastic field and transfers a concentrated load to the fuse, which is subjected to a three-point bending load and dissipates energy through moment-rotation hysteresis loops. The two main goals of the research are to develop a bracing system capable to ensure a stable behavior under cyclic load and easily applicable in structures with several floors to promote a homogeneous dissipative behavior. The main features of the proposed system are the wide customization and applicability in earthquake-resistant steel structures designed according to the capacity design. In addition, the fuse enables expedient repair after a seismic event while ensuring ductile system response. The above considerations highlight the proposed bracing system to be an alternative to the classic X bracing system. In concentric X bracing systems, the seismic energy is dissipated by tensile diagonals, through force-elongation hysteresis loops. The diagonal plastic elongation depends on the member length and the steel's mechanical properties (FEMA 365). In the proposed innovative bracing system, the plastic elongation along the diagonal axis direction is related to the fuse flexural deformation and depends on several design parameters such as the fuse yielding and ultimate moment, the fuse length L, and the second moment of area J of the fuse cross-section. A great number of parameters can be easily modified to satisfy the capacity design rule and ensure a ductile and homogeneous dissipative response of the system. In the bracing system, the dissipation of energy is given by stable moment rotation hysteresis loops, greater than those provided by force-elongation cycles (Bruneau et al. 2011). The fuse is the only member which undergoes plastic deformation, and experimental tests have proved that, after being damaged, its replacement is extremely easy. Results of experimental tests on the full-scale bracing system are presented herein. Tests involve several profiles with different structural details, geometrical features, and mechanical properties.

Fig. 1. Bracing system proposed for different bay with the identification of the fuse

2. Tests 2.1. Geometry of specimens

In the paper, the structural response of the same bracing system, in which only the fuse is changed, is investigated. Fuses belong to the same class 1 (Eurocode 3) but have two different cross-section shapes and connection details (Table 1). Double channel sections (UPN) have about the same elastic section modulus ( W e,xx ) around the strong xx-axis of rectangular hollow sections (RHS). The columns, the long diagonal, and the upper beam are designed as over-strength members and have a rectangular hollow section (150x150x10). The bracing system bay is 2000 mm long and 2000 mm high. The fuse length is L=1000 mm, that is the distance between pinned member-ends; at each end, one bolt M22 grade 8.8 is adopted (see Fig. 1).