Systematic structural evaluation of CSM-strengthened modular timber beams for portable forest bridges

Modular timber beam systems strengthened with chopped strand mat (CSM) present a sustainable alternative for portable forest bridge applications in remote environments, where conventional temporary log bridges frequently experience serviceability reduction due to environmental exposure and limited maintenance. While modular construction offers logistical and sustainability advantages, the introduction of beam segmentation and mechanical connections fundamentally alters structural continuity, significantly influencing stiffness response and dynamic behaviour. Despite increasing adoption of modular timber systems, the combined effects of segmentation and composite strengthening on static–dynamic stiffness characteristics and connection behaviour remain insufficiently quantified, particularly under integrated experimental and numerical evaluation frameworks. This study evaluated the static–dynamic stiffness behaviour of segmented modular timber beams strengthened with CSM, with emphasis on stiffness response, connection load transfer, and performance evolution across varying segmentation configurations. An integrated experimental–numerical approach was employed, comprising Experimental Modal Analysis (EMA) to determine dynamic characteristics, flexural bending tests to evaluate static stiffness, and finite element modelling using ANSYS to validate stress distribution and connection behaviour. Full-scale structural-grade timber beams with a 3.0 m span were tested in continuous and segmented configurations ranging from two to five segments, with and without CSM reinforcement applied to the tension flange. Standardised steel plate and bolt assemblies were used as mechanical connectors, while strain measurements quantified connection-level response under controlled loading conditions. The results demonstrate a strong inverse relationship between static flexural modulus of elasticity and EMA-derived dynamic modulus, attributed to mass augmentation and increased damping effects introduced by composite reinforcement. CSM strengthening improved stiffness retention and modified load transfer mechanisms at mechanical connections, with pronounced load concentration observed at central connectors relative to end connections. Among the investigated configurations, the three-segment system exhibited the most balanced performance, maintaining favourable stiffness response and stable dynamic characteristics, whereas segmentation beyond three segments resulted in pronounced stiffness reduction and increased stress concentration at connection interfaces. The findings confirm the applicability of EMA as a non-destructive evaluation tool for comparative assessment of modular timber systems and establish performance thresholds for segmentation in CSM-strengthened beams. The introduction of the Stiffness Reduction Index (SRI) and Segmentation Performance Index (SPI) provides a systematic framework for configuration-specific performance evaluation, indicating that segmentation should be limited to three segments per 3.0 m span with CSM reinforcement within the investigated scope of portable forest bridge applications.