Investigation of specimen shape and size effect on the in-plane tensile mechanical properties of unidirectional strand board (USB) and oriented strand board/4 (OSB/4)

Strand-based engineered wood products combine high resource efficiency with good mechanical performance. Unidirectional strand board (USB) features strands parallel to the panel’s length, while oriented strand board (OSB/4) has a cross-oriented layup. Understanding their tensile behavior is essential for structural applications, where in-plane tension frequently dictates load-bearing limits. However, large-scale testing guidelines, especially suitable specimen size or shape, remain limited. This exploratory study evaluated tensile properties of USB and OSB/4 using three rectangular specimen sizes (1,200 × 250 mm, 960 × 100 mm, 800 × 75 mm) to assess size effects, and an additional dog-bone OSB/4 group to examine shape effects. USB showed mean modulus of elasticity (MOE) of 8,297–8,762 MPa and Ultimate Tensile Strength (UTS) of 26.8–30.0 MPa, while OSB/4 reached MOE of 4,230–4,617 MPa and UTS of 13.4–14.6 MPa. Statistical analysis isolated size and shape effects from inherent material variability. For USB, a significant UTS size effect was observed: the intermediate specimen (960 × 100 mm) achieved strength comparable to the largest size, proving most efficient. OSB/4 showed no differences between rectangular and dog-bone specimens, confirming rectangular shapes are sufficient. These results indicate trends for optimizing geometries, providing a preliminary basis for future large-scale research toward EN 789 standardization.