重型木框架梁柱螺栓节点弯剪受力性能和变异性研究

Heavy timber structure is a desirable engineering solution for its being green building and having high sustainability, strength-to-weight ratio, fire resistance and durability, etc., and thus has broad application prospects in China. Generally, heavy timber structures have low structural redundancy, compared with light frame wood constructions, since relatively fewer structural elements are used due to their high strength resulted from larger member sizes. Connection plays a key role in the safety and serviceability of the entire structural systems and thus has long been considered as the major difficulty and one of the hot research topics of heavy timber structures. For bolted beam-to-column connections of heavy timber frames, the perpendicular-to-wood-grain tensile failure mechanism and the combined shear and bending resistance of such connections has not been sufficiently incorporated in current design methods and theories, and thus the proposed project is intended to focus on the combined shear and bending resistance and its probabilistic distribution and reinforcing methods of such connections. Full-scale pure shear, pure bending and combined shear and bending tests will be conducted in conjunction with refined finite element method based modeling to identify the interaction law of the shear and bending load effects, as well as to establish a practical correlation curve. Stochastic finite element method based modeling, analysis of covariance and response surface method will be employed to reveal the probabilistic distribution characteristics and to refine the practical correlation curve based on the reliability analysis theories. Connections reinforced with self-tapping screws, locally cross-laminated timber and fiber reinforced polymer sheets will be tested, and the concept of effect reinforcing ratio will be introduced for quantitative evaluation and optimization of the afore-mentioned reinforcing methods, based on which a practical reinforcing design approach will be established based on the effective reinforcing ratio. The framework and the knowledge generated from the proposed research work can be used as reference for improvement of the structural performance and reliability of heavy timber structures and the implementation of relevant design codes, as well as to enhance the academic research and engineering applications of such structural systems in our country, and thus are of both academic and practical significance.

重型木结构木可永久储存碳，减少温室气体排放，且其构件尺寸较大，具有高强、抗火和耐久等优点。然而，重型木结构结构冗余度较低，且有木结构“强构件弱节点”的共性，因而节点性能研究是热点和难点。课题以重型木框架梁柱螺栓节点为研究对象，针对节点弯剪复合受力机制还未被充分认识的现状和体系“强构件弱节点”的特点，研究节点弯剪承载力及其变异性和性能提升方法。以纯弯、纯剪和弯剪复合加载实验和精细化有限元数值模拟为手段，研究节点承载力和弯剪相关关系；以随机有限元、方差分析和反应面方法揭示节点承载力概率分布规律，提出节点承载力取值方法；以采用自攻螺丝、交叉胶合木和碳纤维布缠绕等方法的节点试验和数值模拟量化节点性能提升效应，建立定量分析和计算方法。研究工作可加深对节点受力性能的认识，建立基于概率的节点性能取值方法和定量的性能提升分析方法，改善重型木结构节点和体系性能，提升我国重型木结构的研究和工程应用水平。

课题研究了梁柱螺栓连接节点区域内承受复杂应力的胶合木材料三维弹塑性损伤本构模型的建立方法。课题采用Hill屈服准则和Voce模型描述木材的受压硬化行为，根据Sandhaas提出的破坏准则和不同的损伤变量分别追踪木材的受拉和受压损伤演化过程。和实验结果对比发现：该模型能够合理描述木材在顺纹压应力作用下的强度软化、刚度退化和不可恢复变形，在一定程度上反映木材横纹受压非线性硬化行为，能准确地识别木材横纹受拉和顺纹受剪破坏模式。.课题开展了不同剪跨比梁柱螺栓连接节点承载力性能试验，研究了剪弯比对梁柱螺栓连接节点破坏模式、破坏机理和承载力的影响规律。结果表明：随着剪弯比的不断增加，节点的抗弯承载力和延性比不断降低。与纯弯节点相比，在设计的剪力、剪弯比例荷载作用下弯剪节点的抗弯承载力和延性比的均值最大分别降低了31.7%和15.6%。.课题考虑木材材性和螺孔间隙的随机分布规律，采用随机有限元方法计算了胶合木梁柱螺栓连接节点初始刚度和抗弯承载力。结果表明，销轴承压区顺纹和横纹方向弹性模量对于节点初始刚度的方差具有十分显著的影响，而螺栓孔隙对于节点初始刚度也具有一定的影响；木材横纹抗拉强度和顺纹抗剪强度对于节点抗弯承载力的方差具有显著的影响，而螺栓孔隙也会在一定程度上影响节点的抗弯承载力。.此外，课题研究了碳纤维布包裹、自攻螺丝贯入和局部交叉胶合木等技术对于胶合木梁柱螺栓节点刚度和承载力的提升效应。结果表明，碳纤维布加固技术可有效提高节点极限承载力56.7%、极限变形和耗能能力。课题基于节点破坏机理，提出有效提升率指标α。结果表明，有效提升率α与节点极限承载力提高系数β呈良好的线性关系，根据有效提升率α可以评价不同加固方法的提升效率。.课题研究成果可用于指导胶合木结构设计建造、既有结构安全性评估和改造加固等工程应用，并可拓展相关结构设计规范的应用范围。