| Bamboo-bundle veneer laminated composite(BVLC) is developed as a novel structural panel on the basis of Bamboo-bundle laminated veneer lumber(BLVL), which expands the application of the bamboo-bundle panel in construction to some extent. Therefore, it is imperative that physical and mechanical properties of such panels and their joints connection performance should be studied. Opening connection are two practical ways for BVLC to integrate with other component, due to their performance of high density, difficult surface treatment, etc. Bolted connection is a typical connection mode of opening connection, which leads to bolted connection performance of porous BVLC as main research contents in this study. Main research contents are as follows: Tensile properties of BVLC with three different assemble pattern, upon opening and bolt connection, was studied, as well as the effect of assemble pattern, aperture size and geometry parameters of the bolt joints on bearing performance. Also, the influence law of different off-axis angles and biaxial tensile loading on porous BVLC was investigated, and failure mechanism of porous BVLC under complex stress was obtained. In addition, the effect of assemble pattern, aperture size and axial/ biaxial tensile loading on physical and mechanical properties of BVLC was analyzed by means of finite element numerical simulation software. Finally, failure mechanism and bearing performance of single and multi-bolt connection components within BVLC of three different assemble patterns was explored through full-scale test, based on which three 12 m coupled beam components were designed and manufactured. Further, joints connection of coupled beam components was studied, aiming at providing theory basis for BVLC’s application in engineering.Main results are as follows:(1) Strain gauge method and digital speckle correlation method were both found to study strain distribution law around hole and joint connection well. The results obtained by strain gauge method indicated that maximum strain occurred in both sides of the hole and strain was larger as it located nearer to hole, while minimum strain distribution occurred in the upper part of the hole along tensile direction. Maximum tensile strain appeared in the upper part of the joint in the section of joint connection, while maximum compressive strain underneath joint, which acted as compression face. In comparison, strain distribution around the hole could be more comprehensively observed by digital speckle correlation method, and failure spot around openings and joints could be predicted in advance.(2) This part of study addresses the effects of angle between load and bamboo-bundle fiber(main fiber) grain on the failure model, tensile modulus, and tensile strength bamboo-wood hybrid laminated composite. Seven groups of off-axis tension tests were performed on bamboo-wood hybrid laminated composite specimens. Dog-bone specimens were used for tension testing and were prepared with the angle between the main fiber direction and the loading direction at 0°, 15°, 30°, 45°, 60°, 75°and 90°. The Hankinson’s equation and transformation law were applied to estimate the tensile modulus of bamboo-wood hybrid laminated composite by off-axis test. The failure criteria from four theories: the Hankinson’s equation, Maximum stress theory, Tsai-Hill theory and Hyperbolic equation were applied to predict the off-axis tensile strength of bamboo-wood hybrid laminated composite. The results indicated that both the tensile modulus and tensile strength of bamboo-wood hybrid laminated composite exhibits decreased at first and then increased in the off-axis angle range of 0 to 90°. The tensile modulus and tensile strength at 45°was lower than that of any other angle. There are three kinds of failure modes in off-axis tension test: fiber tensile failure, shearing failure, and cross grain tension failure. The predicted off-axis modulus of elasticity by Hankinson’s equation and transformation law were found to overestimate the results. When calculating the predicted off-axis tensile strength by Hankinson’s equation, Maximum stress theory, Tsai-Hill theory, and Hyperbolic equation the measured values were also overestimated. In order to provide a more accurate prediction of bamboo-wood hybrid laminated composite’s tensile modulus and tensile strength, a revised Hankinson’s equation was developed, which showed good modulus and strength prediction according to grain variation.(3) Biaxial tensile mechanical properties of porous BVLC was obtained that displacement field distribution of E type specimen of 8 mm pore diameter was relatively uniform and shear strain occurred in 45° direction under biaxial load(3000N~4000N in Y direction). Digital speckle correlation method could be used for predicting panel’s damage law in advance. Specimens of different pore diameter were tested under biaxial load(1000N~2000N in Y direction), and average strain along the X direction was found to increase as pore size enlarged, while the opposite for Y direction. Besides, strain range expanded upon the increase of pore size along both X and Y direction.(4) Geometric parameters of bolt joint connection were studied, and results indicated that geometric parameters exert some influence on joint connection. For A type specimen, the joint bearing capacity and connection intensity reached the maximum when W/D=4,E/D=5. For B type specimen, the bearing strength was relatively large and stable when E/D≥4,W/D≥4. For D type specimen, the bearing strength was generally large(approximately 110MPa) and stable when E/D≥4,W/D≥3.(5) Finite element analysis model was found to predict stress state of porous BVLC and the joint connection well, as well as joint connection strength of structural BVLC with different assemble patterns, through which the goodness fit of calculated value and experimental value was relatively high(relative error ≤ 15%). Finite element simulation could be applied to provide certain theoretical support for bolted joint design of BVLC.(6) Full-scale test of 12 m coupled beams was conducted, and the results indicated that the bending rigidity and strength and other performance of fibrous bamboo-bundle veneer double coupled beam were superior to that of parallel-to-grain bamboo curtain coupled beam and bamboo-wood veneer coupled beam. The load value(Deflection limit value L/250) of fibrous bamboo-bundle veneer double coupled beam, parallel-to-grain bamboo curtain coupled beam and bamboo-wood veneer coupled beam was 167.86 kN 、 111.83 kN and 118.94 kN, respectively, and corresponding maximum equivalent uniform load was 15.0 kN/m, 10.0 kN/m and 10.6 kN/m. The investigation on structural bamboo double beam as engineering material was considered to provide new ideas and methods for the application of bamboo engineering material in construction and building. |
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