Design and load-bearing behaviour of joints with fully-threaded-screws pre-drilled with laser-technique - continuation of projekt

采用激光技术预钻孔的全螺纹螺钉接头的设计和承载性能 - 项目的延续

• 批准号: 406036741
• 负责人: Professor Dr.-Ing. Arnold Gillner
• 金额: --
• 依托单位: Lehrstuhl für Baustoffkunde und Institut für Bauforschung (ibac)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/406036741?language=en
• 关键词: Design; load; bearing; behaviour; joints

Due to its important contribution to climate change, sustainable construction with wood is currently experiencing a significant boost, especially in multi-story buildings. Due to the increased loads, the joining points often require fully threaded self-tapping screws (STS) for reinforcement. The use of STS for joining and strengthening timber constructions is also represented in the current Eurocode 5, which will come into force in 2022. At the same time, the use of STS is being investigated in new fields of application, where screws with large engagement lengths (lE = 600 mm and more) are used. However, exact positioning of STS, especially with high lengths, remains challenging. The inhomogeneous wood structure and the high length cause the screws to stray from their designated axis. Pyrolytic pre-drilling utilizing laser radiation represents a suitable and innovative solution method for the exact insertion of STS. The advantages of pyrolytic pre-drilling compared to mechanical pre-drilling with regard to accurate insertion in glulam were worked out in the current DFG project. Within the project suitable process parameters for drilling deep holes in wood and the knowledge about the design of the laser drilling process were developed. Also, the effects on the wood matrix due to heat input were investigated and its influence to the bonding behaviour between the screw thread and the glulam matrix was determined in pull-out tests. Pre-drilled holes up to 300 mm were obtained with a reasonably constant drill cross-section with an average diameter of 6 mm. The gas evolution at greater depths causes more carbonizing burnup throughout the bore channel, adversely affecting the bonding strength of the inserted STS. This results from the stronger heating of the ablation products due to the longer interaction with the laser radiation in the drilling channel during the drilling process. Thus, it is necessary to improve the shielding gas supply to the laser drill point to prevent flames and waste gas disposal from ablating to the drill point. Therefore, for the proposed continuation project, it is planned to carry out the laser drilling process with the aid of a probe with at least one double cross-section for the supply and removal of shielding gas and exhaust gases. The new method improves the supply of inert gas to the ablation point and minimizes pyrolytic burn up due to the heating of the ablation products by the laser radiation. With the help of the newly developed probe, the targeted drilling depth is to be increased to at least 600 mm in this continuation project.

由于其对气候变化的重要贡献，木材可持续建筑目前正在经历一个重大的推动，特别是在多层建筑中。由于载荷增加，连接点通常需要全螺纹自攻螺钉（STS）进行加固。STS用于连接和加强木结构的使用也体现在现行的欧洲规范5中，该规范将于2022年生效。同时，STS在新的应用领域中的使用正在研究中，其中使用具有大啮合长度（lE = 600 mm及更长）的螺钉。然而，STS的精确定位，特别是具有高长度的STS，仍然具有挑战性。不均匀的木材结构和较高的长度导致螺钉偏离其指定的轴线。利用激光辐射的热解预钻孔代表了STS精确插入的合适且创新的解决方案方法。在当前DFG项目中，热解预钻孔与机械预钻孔相比，在准确插入胶合木方面具有优势。在该项目中，开发了在木材中钻深孔的合适工艺参数和关于激光钻孔工艺设计的知识。此外，由于热输入对木材基体的影响进行了研究，并在拔出试验中确定其对螺纹和胶合木基体之间的粘结行为的影响。获得了高达300 mm的预钻孔，钻头横截面相当恒定，平均直径为6 mm。更大深度处的气体逸出会导致整个孔通道中更多的碳化燃耗，对插入的STS的粘合强度产生不利影响。这是由于在钻孔过程中与钻孔通道中的激光辐射的更长的相互作用导致的烧蚀产物的更强的加热。因此，有必要改善对激光钻尖的保护气体供应，以防止火焰和废气处理烧蚀到钻尖。因此，对于拟议的继续项目，计划借助至少一个双横截面探头进行激光钻孔，以供应和移除保护气体和废气。该新方法改善了惰性气体到烧蚀点的供应，并最大限度地减少了由于激光辐射加热烧蚀产物而导致的热解燃烧。在新开发的探头的帮助下，在该延续项目中，目标钻孔深度将增加到至少600 mm。