Technology And Theory Of Bamboo Bundle Laminated Veneer Lumer With Continuous Plate Process

This study originated from the National Forestry Public Welfare Scientific ResearchProgram (201204701), entitled “Key manufacturing technology research and demonstration ofLarge-Span bamboo engineering components”. The research object was as follows. Large-spanbamboo-based coupled beam was exploited for the application of housing construction, whichwas based on the resource advantages of small-diameter sympodial bamboo in China and somebreak-through in technological problem concerning strength, stiffness, durability, design andconnection. The research contents were as follows. The issues of precuring and lengtheningwere solved by the use of one-piece veneer formation, veneer preprocessing densification andintermittent hotpressing technology, and the engineering material was manufactured withcontinuous laminated bamboo-bundle veneer. In addition, the design, manufacture andperformance evaluation of large-span bamboo-based engineering components was conducted.The physical and mechanical properties of boards of different laminated structures weresimulated by finite element analysis software for the optimization of structural design andboard density decrease, which contributed to the manufacture of bamboo-based engineeringcomponents with high ratio of strength to weight.The main research work and corresponding results of this paper are summarized asfollows.(1) The process of bamboo-bundle brooming and one-piece veneer formation wasaccomplished. Through Box-Behnken Design method, the response surface model of BambooBundle Laminated Veneer Lumber was established towards different lengthening process,which showed good precision. In addition, the response surface model was undermulti-objective optimization by genetic algorithm, and17Pareto solutions were obtained.(2) The mathematic model of resin absorption was established between resin absorptionamount of bamboo-bundle, immersion time and PF/PVAC resin mass ratio, and the optimized veneer preprocessing densification process was obtained: preprocessing temperature50-60°C,PF/PVAC resin mass ratio1:6-1:10, preprocessing time15-30min. The parameters of boardswith different resin mass ratio were characterized quantificationally by Fick’s second law andSheldon’s thickness swelling model, including swelling rate parameter KSR, diffusioncoefficient D, swelling activation energy E and diffusion activation energies Ea. The3-Dmodel was established between boiling temperature, water absorption weight gain rate andresidual elastic modulus, which indicated that the higher boiling temperature and weight gainrate, the lower elasticity modulus was obtained. The attenuation law of elasticity modulus vs.time was consistent with the trend of negative exponential function, while the attenuation rateof modulus of rupture was related linearly with weight gain rate.(3) The continuous bamboo-bundle laminated veneer lumber was manufactured byinterval hotpressing technology, and the heat transmission law of intermittent joints wascharacterized quantificationally by Malthus model. The results indicated that appropriatelowering hot-pressing temperature and using cooling water contributed to the decrease ofprecuring degree of intermittent joints. The MOE and MOR of intermittent joints were above16GPa and150MPa, respectively, exhibiting sound mechanical properties. After boiling aging,the degradation and intensity attenuation degree of intermittent joints were larger than that ofthe adjacent ones, and much larger as the immersion temperature increased. There was distinctbrightness variation in CT images of intermittent joints, which indicated the presence offilamentous crack.(4) The bamboo-based laminated coupled beam components were manufactured and thebending properties were compared between bamboo-bundle laminated veneer lumber,bamboo-strips laminated lumber, bamboo-wooden composite and laminated veneer lumber.The design value of coupled beam component was controlled by rigidity of section. Woodencoupled beam components were under brittle failure in midspan when loading, whilebamboo-based coupled beam components under structure displacement. The latter restoredafter the removal of loads, which exhibited great ductility. Bamboo-based coupled beam components performed the highest bending strength, followed by bamboo-wooden coupledbeam components and wooden ones. The strain value of coupled beam components showedlinear variation in section height, which complied with hypothesis of plane mechanism.(5) Eight bamboo-bundle veneer/poplar veneer laminated structures were designed, andthe physical and mechanical properties were sorted into different subsets by SNK method thatperformance index was interchangeable in the same subset. The MOE and MOR were slightlylarger under vertical load than that under parallel load, and the opposite for shearing strength.The laminated structures showed better intensity and rigidity when the bamboo-bundles withconsiderable rigidity acted as surface layers. Results indicated that the laminated structureBBPBPBB had the best overall performance in this study.(6) The laminated prediction model was established by finite element method, and someparameters of boards of different laminated structures were under analog computation withinelastic range and ultimate load, which included deflection, stress distribution, interlaminarstress gradient change and VonMises stress. Laminated prediction model had good precisionthat the trend of calculated value, experimental data and mean subset classification wasconsistent with each other. The stress distribution was linear along thickness direction forlaminated structure of7B and7P, while curved for bamboo-wooden laminated structure.