Experimental and numerical investigation of the static and dynamic behaviour of lightweight long-span steel-wood joist strip systems

Lightweight long-span timber joist floors are susceptible to vibration serviceability issues, yet the influence of connection behaviour and joist spacing on long-span steel-wood joist (SWJ) systems remains insufficiently understood. This study presents a combined experimental and numerical investigation of 8.0 m span SWJ strip systems. Full-scale single joists were tested to characterise stiffness, strength, modal properties, fabrication-related imperfections, and connection behaviour. Double-joist strip systems with centre-to-centre spacings of 450 and 600 mm were subsequently assessed under static loading, experimental modal analysis, and walking-induced vibration. A finite element model incorporating experimentally characterised connection stiffness was developed and validated against measured static deflections, natural frequencies, and walking-induced acceleration responses, with differences generally below 10%. The study provides a unified experimental and numerical assessment of the effects of joist spacing and connection stiffness on the static and dynamic behaviour of long-span SWJ systems. Increasing joist spacing substantially reduced static stiffness while having a comparatively limited influence on fundamental frequency. A 20% reduction in connection stiffness increased mid-span static deflection by up to 11.5%, reduced natural frequency by up to 7.3%, and increased weighted root-mean-square acceleration ( a w,rms ) by up to 88.1%. Conversely, a 20% increase in connection stiffness reduced a w,rms by up to 35.2% and increased natural frequency by up to 5.7%. These results demonstrate that walking-induced acceleration is considerably more sensitive to connection stiffness than static deflection or modal properties.