Numerical Modelling of Timber Trusses for Serviceability Assessment: Accuracy of Pin-Joint and Spring Models

<jats:p>Numerical models of timber trusses used in engineering practice and structural condition assessment typically assume pin-jointed web-to-chord connections. This article demonstrates that such models systematically underestimate measured vertical displacements — by 3 to 44% at the first load point (U₁) and 48 to 70% at midspan (U₂) — which is unsafe from a serviceability assessment perspective. An alternative spring model is proposed in which longitudinal and rotational slip moduli of the connections are incorporated explicitly. Results are presented for six full-scale timber trusses with two fastener types (Wolf 15N punched metal plate fasteners, PMPF, and M10 bolts) and two timber grades (C24 solid timber and GL24h glulam). The spring model reduces the U₁ error to within ±15% for five of six configurations and achieves 3–6% accuracy for midspan displacement U₂ in bolt-fastened trusses. One exception is identified: for the N-web truss with Wolf 15N plates (R1), the spring model overestimates U₁ by 26.5%, attributed to overrepresentation of the rotational spring contribution for that geometry. Experimentally determined longitudinal slip moduli agree well with normative values. Rotational stiffness of Wolf 15N plates is reported experimentally for the first time. Implications for robustness assessment of existing timber roof structures are discussed.</jats:p>