Optimizing hollow-box floor systems with structural composite lumber through screw-gluing method and parametric modelling

Mass timber construction gained significant attention for its sustainability and off-site construction, but conventional mass timber products like cross-laminated timber (CLT) often faces challenges in long-span applications due to material inefficiency. Structural composite lumber (SCL), including mass ply panels (MPP), laminated veneer lumber (LVL), and laminated strand lumber (LSL), can offer a more efficient solution with superior material utilization, dimensional stability, and mechanical properties. This research focused on developing an optimized, prefabricated hollow-box floor system using SCL, integrated with the screw-gluing method and optimization algorithm to improve both structural performance and material efficiency. Experimental tests demonstrated that screws could provide sufficient pressure required by the adhesive instead of a conventional hydraulic press for MPP flange-to-web connections. Key findings indicated that increasing screw spacing, rib width, and flange thickness negatively impact connection performance, with screw spacing reducing shear stress at failure by up to 28%, rib width by up to 45%, and flange thickness by up to 8%. No significant difference in results was observed between groups with 100 mm, 120 mm, and 160 mm long screws in both 50 mm and 75 mm flange groups. Smaller screw spacing improved connection performance, while increasing spacing decreased shear resistance. In the 50 mm flange group, 250 mm spacing was the limit, whereas in the 75 mm flange group, connections with spacing within 300 mm provided acceptable results. ANOVA results indicated that rib widths of 75 mm or more reduced connection performance with a single screw row arraignment but performed acceptably with staggered two row arrangement. Flange thicknesses also had a minor influence, with increased thickness from 75 mm to 100 mm negatively impacting load-carrying capacity by 8%. These findings provided essential insights into fabricating hollow-box floors using the screw-glued technique. In addition, a parametric optimization algorithm was developed by integrating parametric geometry modelling, material databases, design verification methods, including the stressed skin design method in CSA O86, Gamma method, and the shear analogy method. Genetic algorithm was also used to automatically iterate through input parameters, overcoming the drawbacks of conventional, manually iterative, and time-consuming structural design process. The study also compared different methods for calculating the effective width of hollow-box floor modules, with CSA O86 and Kikuchi methods yielding similar results, while Eurocode 5 provided more conservative estimates. The optimization results demonstrated that hollow-box floor systems could achieve up to 75% material savings compared to CLT and 67% compared to solid MPP panels, while also reducing floor height by approximately 30% relative to I-joist systems under deflection-controlled conditions. Furthermore, vibration-controlled criteria were considered as an additional optimization objective, achieving up to 60% and 50% material savings compared to CLT and MPP solid panels, respectively.