Behavior and Failure of Wood-Nailer Steel Joist Systems Using Shell and Hybrid FE Models

Wood-nailer (WN) steel joists form a composite structural system in which cold-formed steel top and bottom chords and web members, a wood nailer, and screw connections act together to resist load. This study investigates the nonlinear system behavior and failure characteristics of WN-series joists using high-fidelity finite element (FE) analysis, with emphasis on comparing full shell–solid models to a computationally efficient hybrid model suitable for system-level response prediction. Eight joist configurations were analyzed using geometrically and materially nonlinear Static General procedures. The shell model employed S4R shell elements for all cold-formed steel components and solid elements for the wood nailer, whereas the hybrid model represented webs and bottom chords using B31OS beam elements while retaining shell–solid contact for the top chord and wood nailer. This approach captures composite interaction while substantially reducing computational cost. Both models demonstrated strong agreement in overall system response. Load–displacement curves from the shell and hybrid models closely matched across all joist types, and both modeling approaches consistently predicted the same failure modes. Across all configurations, failure was governed by yielding in either the end-web region or the bottom chord, and the shell and hybrid models showed excellent agreement in identifying these governing failure mechanisms. These results show that the hybrid model can reliably reproduce the system behavior and structural response observed in the full shell model. The hybrid modeling strategy successfully captures essential system-level mechanics, including steel–wood interaction and global deformation patterns, while providing a substantial reduction in computational demand. The findings validate the hybrid model as an effective tool for large-scale system studies and future sensitivity or uncertainty investigations, and they improve understanding of WN-joist system behavior within the broader context of frame and system analysis.