Bond behaviour of self-tapping screws with continuous threads and long embedment length being used as reinforcement in glue-laminated timber elements - long-term behaviour

在德国研究基金会(DFG)资助的本研究项目中，通过拔出和载荷分配试验，系统地研究了胶合木构件中带连续螺纹的自攻螺钉在短期载荷下的粘结性能。通过集成数字摄影测量方法，可以覆盖螺丝与颗粒不同角度的整个锚固的应变状态。根据木材的蜂窝结构和天然(有机)材料特性，木材在不同气候条件下的蠕变和收缩表现出不可忽略的影响因素，这对复合材料螺杆-木材粘结基质的承载性能有重要影响。为此，在最初的申请中涉及了对长期负荷影响的调查，但它们已被排除在批准范围之外。在已经进行的实验研究的基础上，应进一步系统地、解析地和数值地分析长期加载对粘结行为的影响。这项调查的目的是描述在长期载荷和周期性气候变化下债券行为的变化。所开发的锚具设计模型可用于长期加载，从而可以用有限元方法模拟粘结性能。

In the course of the current research project, funded by the German Research Foundation (DFG), the bond behaviour of self-tapping screws with continuous threads in glue-laminated timber elements has been systematically investigated under short term loads by means of pull-out and load distribution tests. Through integration of digital photogrammetric methods, it was possible to cover the strain-conditions of the whole anchorage of the screws in different angles to the grain. Therefore, the effect of the anisotropy on the anchorage of self-tapping screws in wood matrix has been visualized.According to the cellular structures and natural (organic) material characteristics of wood, its creeping and shrinkage in varying climates displays not negligible factors of influence, which have significant impact on the load bearing behaviour of the bond matrix of the composite material screw-wood. For this purpose, the investigations on the influence of long term loads have been involved in the primal application, but they have been excluded in the approval. The already conducted experimental inves-tigations should be complemented with further systematic, analytic and numeric analysis of the influ-ence of long term loading on the bond behavior. The investigation is aiming at creating a description of the changes in the bond behaviour under long term loading and cyclic climate changes. The devel-oped design model for the anchorage can thereafter be approved and adopted for long-term loading, thus enabling the simulation of the bond behavior with the finite element method.