PSI - Issue 44

Giacomo Iovane et al. / Procedia Structural Integrity 44 (2023) 1864–1869 Giacomo Iovane et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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concentric or eccentric braced structures, widely used in the seismic resistant steel structures (Faggiano and Iovane, 2016). Since timber is a material with an elastic-fragile behaviour, in the present anti-seismic regulations, such as in Europe the Eurocode 8 (EC8, EN 1998-1: 2005), it is indicated that the joints could dissipate through the plastic deformations of metallic connectors. However, joints are structural elements with an important role in bearing the design loads. Therefore, in order to possibly design dissipative timber structures, the dissipation capacity should be provided by ad hoc conceived devices. Very efficient solutions are steel links, located in timber members depending on the seismic resistant structural type, which are able to provide a significant dissipative capacity if designed with adequate strength, stiffness and ductility, while the timber members and the steel connections should be designed with an adequate over-strength, to remain in elastic field (Faggiano and Iovane, 2016; Faggiano et al., 2018; Iovane et al., 2021; Iovane and Faggiano, 2021). Some recent researches have focused on the development of hybrid timber-steel, instead of relying on an all timber structures, showing good potential for improving the behaviour of seismic resistant timber structures (Humbert et al., 2013, 2014; Komatsu et al., 2014; Nakatani et al., 2012). Aiming at the optimization of either structural systems and joints or design criteria, Montuori and Sagarese (2018) have applied the steel reduced beam sections, commonly proposed for steel MR frames (Faggiano et al, 2003; Montuori, 2014), to timber beams. Tomasi et al. (2008) and Andreolli et al. (2011), as well as Gohlich et al. (2016, 2018), focused on a beam-column timber joint equipped with steel links for dissipative heavy timber Moment Resisting Frames (MRF). Gilbert et al. (2015) have also studied a steel-timber buckling restrained braced frame. In this context, the paper deals with the design of heavy timber framed structures with dissipative steel link. In particular, 2D single-storey structures equipped with links, in different configurations, such as MRF, Concentric (CBF) and Eccentric (EBF) Braced Frames, are studied. The design criteria are proposed according to the capacity design approach, with the aim to allow the plastic hinge formation in the steel links, while the timber member are designed to remain elastic, with adequate overstrength. The mechanical characterization of the dissipative structures is carried out through non-linear static numerical analyses, by means of the structural calculation program SAP2000. The efficiency of the design criteria applied is evaluated in terms of structural mass and seismic behavior, evaluated in terms of push-over curves, behavior q-factor. Results are compared to those of non-dissipative structures. 2. Design of heavy timber framed structures with dissipative steel links 2.1. Design criteria Seismic resistant timber buildings are designed in accordance with one of the following concepts, as provided in section 6.1.2 of EC8 (EC8, EN 1998-1: 2005): Low (DCL) and High or Medium dissipative structural behaviour (DCH and DCM). In DCL concept, the action effects are calculated on the basis of an elastic global analysis disregarding the non-linear material behaviour and considering a behaviour factor q ≤ 1.5. The resistance of timber members and connections should be evaluated in accordance with Eurocode 5 (EC5; EN 1995-1-1: 2005). In DCH and DCM concepts, dissipative zones are assumed to be located in the steel links, which should have high ductility capacity, with cross sectional classes 1, 2, whereas timber members and steel connections should be elastic. To ensure yielding of the dissipative zones, all non-dissipative members, such as timber beams, columns and diagonal, as well as the connections in DCM and DCH structures should be designed according to hierarchy resistance criteria, on the bases of the design strength of the ductile parts, through the application of an overstrength factor, which should be adequately defined in function of the structural type and the behaviour of the dissipative link according to the EC8 (EC8, EN 1998-1: 2005; Faggiano et al., 2016). For DCH and DCM structures the behavior factor is q >1.5, in function of the energy dissipative capacity (Calderoni et al, 2019). With regards to the structural configurations, in case of MRFs steel links are placed at the beam ends and at the column bases, they should be designed so that the seismic energy dissipation occurs through the plastic deformation of the links for cycles of bending moments; in case of CBFs (V, D and X) steel links are placed at the braces ends, they should be designed so that the seismic energy dissipation occurs through the plastic deformation of the links for cycles of axial forces; in case of EBFs steel links are generally placed at the timber beam, they should be designed so that the seismic energy dissipation occurs through the plastic deformation of the links for cycles of bending moment (long-link) or shear (short-link) or bending moment and shear (intermediate-link; Faggiano et al, 2016).