PSI - Issue 78

Giacomo Iovane et al. / Procedia Structural Integrity 78 (2026) 528–535

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Formed Steel (CFS) frames combined with timber OSB or plywood panels, used to realize both vertical and horizontal diaphragms. They achieve significant improvement of in-plane stiffness and strength compared to all-steel frames, playing a key role in deformation control and force distribution (Landolfo et al., 2006; Nagao et al., 2025). Type 1.1 Type 1.2 Type 1.3

Dickof, 2013

Loss et al., 2016

He et al., 2014

Li et al., 2021

Nagao et al., 2025 Landolfo et al., 2006

Fig. 2. Type 1 steel frames with timber shear walls.

Among Type 2, it is possible to identify the following most common system configurations: (2.1) steel frame with mass timber diaphragm ; (2.2) steel frame with light-weight timber diaphragm . These systems are characterized by reduced mass and great sustainability, offering an alternative to traditional concrete floors. Type 2.1 hybrid system consists of steel frames combined with CLT horizontal panel to provide a rigid floor. This solution exhibits in-plane stiffness similar to that of traditional reinforced concrete floors and leads to a significant reduction of the stress demands on the structural steel members and of slipping, improving the overall structural efficiency (Asiz and Smith, 2011). Composite behavior, stiffness and ductility of the hybrid floor systems are strongly influenced by type and arrangement of the screw connections between the steel beams and the CLT panel (Li et al., 2016; Loss et al., 2017; Deeves et al., 2025; Laughery et al., 2025). Further improvements in composite performance can be achieved using adhesive connections, such as a two-components non-sag gel type structural epoxy adhesive, which improve the interaction between CLT panels and steel beams, reducing slipping, thus increasing the system load-bearing capacity (Hassanieh et al., 2016). Furthermore, CLT panels are also combined with thin-walled C-section steel beams and Cold Formed Steel (CFS) elements, achieving excellent results in terms of flexural strength and overall diaphragm performance (Navaratnam et al., 2021; Owolabi and Loss, 2025). Type 2.2 hybrid system involves the use of light weight timber floors, such as OSB panels or, more rarely, bamboo plywood panels, connected to the steel structure. Experimental studies have confirmed the consistency of the system ’ s bending behavior with analytical predictions (Xu and Tangorra, 2007; Li et al., 2012). The shear interaction between the steel structure and the light-weight timber floor plays a crucial role in the system performance. Quantitative evaluations are performed through experimental campaigns and numerical simulations, leading to the development of predictive models and design methods for estimating the shear coefficient and optimizing connection layouts (Kyvelou et al., 2015; 2021).

Type 2.1

Type 2.2

Li et al., 2021

Li et al., 2012

Kyvelou et al., 2021

Fig. 3. Type 2 steel-timber hybrid and composite floor diaphragms.

Among Type 3, it is possible to identify the following most common system configurations: (3.1) hybrid frame with steel columns and timber beams, slabs and walls ; (3.2) timber frame with steel members and joints ; (3.3) timber frames combined with steel frames . Type 3.1 hybrid system is characterized by steel columns combined with timber beams, CLT floors and shear walls. These systems often include friction connections at the beam-column interface as