Performance-Based Evaluation and Design of Cold-Formed Steel Lateral Force-Resisting Systems for Multi-Storey Buildings

Cold-formed steel (CFS) is becoming popular in building construction as it is more economical and
lightweight compared to conventional hot-rolled steel whilst offering ease and speed of construction and
greater flexibility in manufacture. However, due to the low element thickness it is more prone to
buckling; hence, the design of elements and structures is more challenging, especially when called to
resist lateral loads, like wind and earthquakes. While CFS strap-braced stud walls can be used to provide
light steel frames with high lateral strength and stiffness, more research is needed to investigate their
seismic performance. Furthermore, secondary moments due to P-Δ effects, amplified by the presence of
additional vertical loading, are generally ignored in conventional design and can lead to premature
failure of compressive studs and low ductility.
In this research, the non-linear behaviour of CFS strap-braced stud walls is comprehensively examined
to improve structural efficiency. By considering P-Δ effects, the key design parameters are identified,
and a novel design framework is developed. CFS multi-storey frames are analysed numerically, and the
efficiency of the proposed methodology is investigated by using local and global damage indices under
seismic loading with different intensity levels. Finally, the work focuses on the development of new
types of CFS moment-resisting beam-column joints, transferring bending moments through the flanges
or both the webs and flanges, and design considerations are proposed to reach a balanced performance,
combining high flexural capacity, deformability, ductility and rotational stiffness.
The results of this study indicate that diagonal strap thickness and vertical loading had the most
significant impact on critical seismic performance parameters, such as the lateral load and deformation
capacity, ductility and energy dissipation. A case study 6-storey strap-braced frame, designed in
accordance with Eurocode 8 specifications, exhibited very low ductility at some storey levels, below the
target value of 4, while the design solution following the proposed methodology reached high ductility,
preventing premature failure of the chord studs. The efficiency of Eurocode 8 and the proposed design
solutions was studied and assessed under artificial and real spectrum-compatible ground motion records
using non-linear dynamic analyses. The proposed design solution met all target performance levels and
reached low damage index values. By contrast, Eurocode 8 design solution failed to meet the life safety
(LS) and collapse prevention (CP) targets while sustaining extensive global damage even under low
earthquake intensity levels of 0.20 g.
The newly developed flange and web-flange connected joints proved to be an appropriate and efficient
alternative solution to web-connected joints, exhibiting high bending moment capacity, ductility and
energy dissipation while facilitating assembly. The results of this research have the potential to
contribute to the development of more resilient CFS strap-braced systems in seismic regions.