Research On Bearing Performance Of Bolt Joint For Recombinant Bamboo

Connection is the key design in wood and bamboo structure. The whole structure damagesare always originated by the connection failure. With the development of modern bamboostructure, bolt joint with the traits of simple, safe and reliable, easy to use and so on，has beenused widely. Recently, there was little report on the bolt joint of recombinant bamboo, so it isimportant to study it, for it has an important role in improving the safety and reliability of boltjoint, and providing theoretical basis for its further promotion.Recombinant bamboo that produced by Moso bamboo (Phyllostachys pubescens) wastaken as test material. This research focused on the performance of bolt joint for recombinantbamboo, such as analyzing the effect of several factors on dowel-bearing and bolt jointperformances, observing failure mode and exploring failure mechanism. Besides, theapplicability of the wood-bolted design formula was evaluated for recombinant bamboo. Inaddition, based on the characteristics of recombinant bamboo, theoretical calculation formulasof dowel-bearing strength and bearing capacity were derived, which are benfit for theapplication of bolt joint in modern bamboo structure, providing reliable theoretical basis forperformance improvement of bamboo structural bolt joint, new-typed structural connectiondevelopment.The main results of this research are summarized as follows：1. Recombinant bamboo has uniform density, high mechanical strength and stability,which satisfies the mechanical strength requirements of structural material. Twelve elasticconstants, fracture toughness of modeⅠin TL and RL direction of recombinant bamboo wereobtained. The thickness of the fracture toughness sample for recombinant bamboo wasrecommended to set as25mm. The bending yield strength of bolt increased with the boltdiameter. 2. As to the dowel-bearing strength, there was no significant dimension effect if sampledimension satisfy the minimum requirements. Besides that, bolt diameter, grain angle andmoisture content have significant effect on the dowel-bearing strength.It decreased with theincrease of bolt diameter. It decreased first and then increased with the grain angle increase. Itshowed a decreasing trend with the moisture content increases, and became constant gradually.3. When the grain angle changed from0°to90°, failure mode is from a mixturedamage of the spitting parallel to the grain and crushing on the ends of dowel-bearing sample,to a mixture damage of groove crushing and whole sample crushing (layered crack along thethickness direction of the sample), the45°dowel-bearing sample was as a turning point.4. The dowel-bearing strength prediction values from the wood dowel-bearing strengthformula in Eurocode5and NDS/LRFD were much smaller than the test values. Therefore,theoretical design equations of dowel-bearing strength for recombinant bamboo wereconstructed by introduced bolt diameter, moisture content and grain angle as considerationfactors. Besides, the standard dimension of dowel-bearing strength test samples was arised.5. The effect of end distance, main member thickness and bolt diameter on bearingperformance of single-bolted connection (initial stiffness, post-yield stiffness, yield load,ultimate load and ductility rate) were obtained. A minimun main member thickness ofrecombinant bamboo joints was recommended to set to90mm. the theory formula ofsingle-bolted joint was derived based on dowel-bearing strength, factor effect of recombinantbamboo.6. The load-deformation curves of single-bolted connection simulated by Foschi modelare so well, it could reflect the elastic and yield region characteristics and the transition ofelastic to plastic, visually. Beside, there are two effective failure modes for single-boltedconnections,“one-hinge” and “two-hinge” yield mode. Both of the two failure modes arereasonable, in which the main member and bolt can exert their mechanical properties fully.7. The change trend of bolt rows, row space, the space between adjacent bolts and boltnumbers in each row on the bearing performance of multi-bolted joints were summarized. With the increase of space between adjacent bolts, the failure mode changed from the mixture of rowsplit and “one-hinge” yield to simple hinge yield, gradually. In multi-bolted joints, with the boltrows increase, the failure changes from single split to the both sides split. The split graduallydisappeared with the increasing row spacing, only the dowel-bearing and hinge yield failureemerged. For the non-uniform load distributions, the middle bolts had less deformation thanthe others.8. The effect of end bolt space, bolt and row number on bearing performance ofMulti-bolted connection were obtained.With the increase of bolt number, the yield phase of theload-displacement curve is even more short-lived. Several load-deformation curves almostdirectly changed from the linear elastic stage to destruction stage. Beside, the effective boltnumbers and reduction coefficients those based on the single-bolted connection are calculated,and the theory formula for Multi-bolted joint aslo been derived.