Prediction of bending moment resistance of screw connected joints in plywood members using regression models and compare with that commercial medium density fiberboard (MDF) and particleboard

The study aimed at predicting bending moment resistance plywood of screw (coarse and fine threads) joints using regression models. Thickness of the member was 19mm and compared with medium density fiberboard (MDF) and particleboard with 18mm thicknesses. Two types of screws including coarse and fine thread drywall screw with nominal diameters of 6، 8 and 10mm and 3. 5، 4 and 5 cm length respectively and sheet metal screw with diameters of 8 and 10 and length of 4 cm were used. The results of the study have shown that bending moment resistance of screw was increased by increasing of screws diameter and penetrating depth. Screw Length was found to have a larger influence on bending moment resistance than screw diameter. Bending moment resistance with coarse thread drywall screws was higher than those of fine thread drywall screws. The highest bending moment resistance (71. 76 N. m) was observed in joints made with coarse screw which were 5 mm in diameter and 28 mm in depth of penetration. The lowest bending moment resistance (12. 08 N. m) was observed in joints having fine screw with 3. 5 mm diameter and 9 mm penetrations. Furthermore، bending moment resistance in plywood was higher than those of medium density fiberboard (MDF) and particleboard. Finally، it has been found that the ultimate bending moment resistance of plywood joint can be predicted following formula Wc = 0. 189×D0. 726×P0. 577 for coarse thread drywall screws and Wf = 0. 086×D0. 942×P0. 704 for fine ones according to diameter and penetrating depth. The analysis of variance of the experimental and predicted data showed that the developed models provide a fair approximation of actual experimental measurements.