The bending performance of T&G joints subjected to concentrated loads

In Part 1 of this research work, a description of the small-scale concentra ted load test is presented. Unjointed and jointed (glued/unglued) particleb oard samples were subjected to a mid-span concentrated load up to failure. The failure loads were compared and conclusions were drawn with regard to t he influence of gluing the T&G joints on the structures' resistance to conc entrated loads. The stiffness, considered to be the slope of the linear region of the load- displacement chart has been calculated. Linear regression lines between fai lure load and stiffness were sought. Relatively good correlation (R-2 = 0.8 8) was found for the unjointed samples, however, less good correlation (R-2 = 0.63) was found for the glued jointed samples and even worse correlation (R-2 = 0.53) was found for the unglued jointed ones. Generally, the stiffn ess can be considered as a useful indicator for the failure load and failur e mode of the particleboard samples. For increased stiffness values the boa rds tend to fail at higher loads and in a more brittle mode, providing a su dden vertical drop in the load/displacement curves. At values over 456 N/mm 'catastrophic' failure modes (instant total failures) were observed (span size of 450 mm and thickness of the boards of 18 mm). However, at values le ss than 420 N/mm the failure mode was more ductile, described by 'smooth' p ost failure curves. By gluing the joints the stiffness of the structure inc reases significantly. The failure load also increases but not by an amount that is statistically significant. The failure mode of glued jointed struct ures seems to be more ductile when compared to unglued ones. This means tha t after the maximum failure load has been achieved, the boards continue to sustain the load for a longer period of time up to ultimate failure occurs.