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）资助的当前研究项目中，通过拔出和载荷分布试验，系统地研究了胶合木构件中具有连续螺纹的自攻螺钉在短期载荷下的粘结性能。通过数字摄影测量方法的集成，可以覆盖不同角度的螺钉对晶粒的整个锚固的应变条件。根据木材的细胞结构和天然（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视的影响因素，对自攻螺钉-木材复合材料粘结基体的承载性能有重要影响。为此，在初步应用中已涉及长期荷载影响的研究，但在批准中已将其排除。已经进行的试验研究应补充长期荷载对粘结性能的影响的进一步系统、分析和数值分析。调查的目的是创建一个长期的负载和循环气候变化下的债券行为的变化的描述。开发的锚固设计模型可用于长期荷载，从而能够用有限元法模拟粘结性能。

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.