Structural Performance of Timber Connections with Long Self Tapping Wood Screws

长自攻丝螺丝(STS)是欧洲最近的一项重要发明，旨在加强木材固有的弱点，如垂直于纹理强度的拉伸和压缩以及纵向剪切强度。这些螺丝在欧洲被广泛用于加固遭受过度裂缝的大型木材/胶合板梁。除了加强的作用，这些螺丝也可以用来在木材连接中提供主要的载荷传递。在北美，这些螺丝还不流行；拉力螺栓的代码规定与STS的应用最相似。然而，这些规定忽略了这些连接件最重要的特点，即它们的抽拉能力和与木纹成角度施加的刚度；因此，这些规定是不合适的。在欧洲为不同品牌的专有STS产品开发了大量的STS数据库，每种产品都有自己的技术批准，可以主要适用于欧洲物种(云杉和松树)。对欧洲设计条款的初步评估表明，它们不适用于北美树种，因为那里的木材和密度范围内的节结结构与欧洲木材非常不同。此外，还没有关于这些螺丝钉在结构复合材应用中的应用的信息，例如单板层积材和平行单板材；因此，需要做大量的工作来了解STS的性能并量化STS在北美的应用。

Long self-tapping wood screw (STS) is an important recent European invention intended to reinforce the inherent weaknesses of wood such as the tension and compression perpendicular to the grain strengths and longitudinal shear strength. These screws are widely used in Europe to reinforce large timber/glulam beams that have suffered from excessive cracking. Besides the role of reinforcements, these screws can also be used to provide primary load transfer in timber connections. In N. America, these screws are not yet popular; code provisions for lag bolts have the closest resemblance for the applications for STS. However, these provisions ignore the most important feature of these connectors, namely, their withdrawal capacity and stiffness applied at an angle to the wood grain; therefore, these provisions are not appropriate. The extensive database developed in Europe on STS for different brands of proprietary STS products, each having its own technical approval, can be applied mainly to European species (Spruce and Pine). Preliminary evaluation of the European design provisions indicates that they are not suitable for N. American species where the knot structures in the wood and density range are very different from European wood. Also there is no information on the application of these screws in application of structural composite lumber such as laminated veneer lumber and parallel strand lumber; therefore, significant work is needed to understand the behaviour and quantify the performance of STS for applications in N. America.