Creep Properties Of Bamboo-based Engineering Composite Material Applied In Structure

Creep is an important evaluation indicator to determine whether one material could be used for long-span structure or not. With the ever increasing application of bamboo in modern architectures, its loading stability becomes the key problem needs to be solved. The goal of this thesis is to build the creeping model of bamboo laminated veneer lumber and glued laminated bamboo to obtain its allowable stress and calculate its long-time loading performance.The content of this thesis can be given as follows:Firstly the variation of the bending creeping performance at the radial direction was studied. The influence of loading direction and the content of vascular bundle on the creeping were also discussed.Then, the time-temperature superposition principle(TTSP) and the mechano-sorptive creep model were employed to study the influence of time and humidity change on the bending creeping performance of Bamboo laminated veneer lumber and glued laminated bamboo.Finally, the one-year creeping and recovering experiment were conducted to obtain the creeping law of the bamboo materials, which were then used to build the constitutive model for long time prediction.The conclusions were listed as follows.1 The yellow side of the bamboo presented a better anti-creep performance than that of the green side. For the compress condition at the green side, the outer side presented a best anti-creeping performance, lowest initial deflection, and lowest increase rate of creep. For the compress condition at the yellow side, the initial deflection of the outer side was the largest but the deflection increasing rate became lower than the middle and inner side with the loading time, which were related to the fiber content and character of the parenchyma cell.2 The variation law of the creep between the tangential direction and the radial direction were found to be different. The former depended on the contribution of the bonding interface and the later depend on the uniformity of the fiber in the cross area.3 The TTSP could be used for the prediction of long time creeping behavior of Bamboo laminated veneer lumber and glued laminated bamboo. The time-temperature-moisture curvecan be used for viscoelastic behavior description of the environment with the moisture range from dry to 30% and the activation energy range from 47Kcal/mole to 76 Kcal/mole.4 The variation law of the mechano-sorptive creep between bamboo laminated veneer lumber and glued laminated bamboo were found to be different. The increase of the creep of the former and the later were induced by desorption and the absorption, respectively, which can be explained by difference of the material properties such as the element size, fiber orientation, and the moisture absorption character. The convergence values of mechano-sorptive creep for bamboo laminated veneer lumber and glued laminated bamboo were determined as 1.293 mm and 3.363 mm, respectively.5 The creep deformation of bamboo laminated veneer lumber and glued laminated bamboo can be described by three stages as elastic stage, viscoelastic stage and plastic stage. The Burgers model was proved to be able to accurately describe the stage of elastic stage and viscoelastic stage. The anti-creep performance of bamboo laminated veneer lumber was found to be better than that of the glued laminated bamboo. The allowable stress of the bamboo laminated veneer lumber and glued laminated bamboo were obtained as the 16.6% and 19.05% of the maximum load, respectively.