| This study proposes a reinforcement method of improving the axial compressive strength of bamboo by GFRP(glass-fiber reinforced polymer)sheet wrapping.Take moso bamboo(phyllostachys pubescen)as the object of study,conducting experiments on mechanical properties,macroscopic and mesoscopic characteristics and bamboo structure reinforced by GFRP.The main work and achievements of this study are shown below:(1)Experiments on axial compression strength are carried out on 127 bamboo specimens,including 5 specimen sizes,different selection parts of bamboo and the effects of bamboo node.Failure mode,load bearing capacity and deformation of specimens are obtained.The failure mode of bamboo under axial load is longitudinal fiber cracking caused by out-of-plane bulging deformation,changing the close ring section of bamboo to the open ring section which leading a greatly decreased of compressive strength.The average length of bamboo stalk is 7?8m.The average compressive strength difference between local internode is within 5%,however the compressive strength of bamboo from the top increased by 6.4%?12.2% comparing with the bottom.The fibers are bent and discontinuous at the node,the compressive strength of bamboo with node decreasing by 1.5%?10.3%,and the negative effect on bottom is the most significant.32 tests are performed and the tensile strength of bamboo increased by 6.9%?17.5% from bottom to top.Specimens with node have lower tensile strength than without by 1.3%?24.2%.According to the analysis of 18 shear tests,the shear strength of bamboo is less affected by the different seletion parts,but the specimens with node decreased the shear strength by 32.4% at most.In the 12 ring stiffness tests,the ring stiffness of top specimens are 116.5%?130.5% higher than the bottom,while the ring stiffness of specimens with node significantly increased by 69% and the compressive bearing capacity increased by 92.1%.(2)The mechanical properties of moso bamboo show a functionally gradient distribution in both longitudinal and radial direction.In order to obtain the axial compressive strength at different selection parts of bamboo,a non-destructive method of predicting the compressive strength of bamboo is developed.The main variables include internode length,perimeter,cross section area,wall thickness,vascular bundles area ratio,and moisture content,etc.By analyzing the macroscopic and mesoscopic characteristics of 30 bamboo stalks and axial compression tests,the fitting formula of vascular bundles area with perimeter is proposed to evaluate the compression bearing capacity of moso bamboo,which can provide theoretical reference for engineering.(3)The tests of bamboo reinforced by GFRP wrapping are carried out,comparing 87 specimens for 3 type of different reinforcement methods.The compressive strength of specimens partial wrapping with GFRP at both ends increased only 13%,while specimens partial wrapping in the middle increased 61%.After reinforcement,the failure modes of specimens complete wrapping with GFRP are changed from bulging to progressive inward folding buckling and end crushing failure,which is similar to the FRP pipe.The increase of compressive strength is proportional to the number of wrapping layers but inversely proportional to diameter of specimens.The maximum compressive strength of 4 GFRP wrapping layers can be increased by 233%.In the tests of 2 type of bolt joints,the unreinforced specimens often be cracked at the bolt hole,while wrapping with GFRP can restrain the crack propagation and maintain the bearing capacity of the bolt joint which improves the safety of the bamboo structure.By literature research and experimental studies,the evaluation method of mechanical properties of moso bamboo is proposed,and the feasibility of reinforced bamboo with GFRP is confirmed.This study provides technical and theoretical supports for engineering of bamboo structure. |
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