Domínguez Manuel, Fueyo Jose G, Villarino Alberto, Anton Natividad
Department of Mechanical Engineering, Continuum Mechanics Area, High Polytechnic School of Zamora, University of Salamanca, Avda. Requejo 33, 49022 Zamora, Spain.
Department of Construction and Agronomy, Construction Engineering Area, High Polytechnic School of Ávila, University of Salamanca, Hornos Caleros 50, 05003 Avila, Spain.
Materials (Basel). 2021 Dec 29;15(1):242. doi: 10.3390/ma15010242.
Dowel-type fasteners are one of the most used type of connections in timber joints. Its design follows the equations included in the Eurocode 5. The problem with these equations is that they do not adequately contemplate the resistive capacity increase of these joints, when using configurations which provoke the so-called rope effect. This effect appears when using threaded surface dowels instead of flat surface dowels, expansion kits or nut-washer fixings at the end of the dowel. The standards consider this increase through a constant value, which is a poor approximation, because it is clearly variable, depending on the joint displacement and because is much bigger, especially when using nut-washer fixings. It is also very important because of the rope effect trigger interesting mechanisms that avoids fragile failures without warning of the joints. For these reasons, it is essential to know how these configurations work, how they help the joint to resist the external loads and how much is the increase resistance capacity in relationship with the joint displacement. The methods used to address these issues consisted of a campaign of experimental tests using actual size specimens with flat surface dowels, threaded surface dowels and dowels with washer-nut fixings at their ends. The resistance capacity results obtained in all the cases has been compared with the values that will come using the equations in the standards. After the tests the specimens were cut to analyze the timber crushings, their widths, the positions and level of plasticizations suffer in the steel dowels and in the washer-nut fixings and the angle formed in the dowel plastic hinges. With all this information the failure mode suffered by the joints has been identified and compared with the ones that the standards predict. The results for the size materials and types of joints studied shows that the crush width average values go from 20 mm with flat surface dowels, to 24 mm in threaded to 32 mm in threaded with washer-nut fixings. The rope effect force/displacement goes from 100 N/m in threaded surface dowels to 500 N/m in threaded with washer-nut fixings. Finally, the load capacities are on average 290% higher those indicated in the standard. The main conclusion is that the rope effect force should be considered in the standards in more detail as a function of multiple variables, especially the displacement of the joint.
榫钉式紧固件是木结构节点中最常用的连接类型之一。其设计遵循欧洲规范5中的公式。这些公式的问题在于，当使用会引发所谓绳索效应的配置时，它们没有充分考虑这些节点的承载能力增加情况。当使用螺纹表面榫钉而非平面榫钉、膨胀套件或榫钉末端的螺母垫圈固定件时，就会出现这种效应。标准通过一个恒定值来考虑这种增加，这是一个很差的近似值，因为它明显是可变的，取决于节点位移，而且特别是在使用螺母垫圈固定件时，其值要大得多。由于绳索效应引发了有趣的机制，可避免节点无预警的脆性破坏，所以它也非常重要。出于这些原因，了解这些配置如何工作、它们如何帮助节点抵抗外部载荷以及与节点位移相关的承载能力增加量至关重要。用于解决这些问题的方法包括开展一系列实验测试，使用实际尺寸的试件，试件采用平面榫钉、螺纹表面榫钉以及末端带有垫圈螺母固定件的榫钉。将所有情况下获得的承载能力结果与使用标准公式得出的值进行了比较。测试后，对试件进行切割，以分析木材的挤压情况、其宽度、钢榫钉以及垫圈螺母固定件中发生塑化的位置和程度，以及榫钉塑性铰形成的角度。利用所有这些信息，确定了节点所遭受的破坏模式，并与标准预测的模式进行了比较。所研究的尺寸材料和节点类型的结果表明，挤压宽度平均值从平面榫钉时的20毫米，到螺纹榫钉时的24毫米，再到带有垫圈螺母固定件的螺纹榫钉时的32毫米。绳索效应力/位移从螺纹表面榫钉时的100牛/米，到带有垫圈螺母固定件的螺纹榫钉时的500牛/米。最后，承载能力平均比标准中指出的高290%。主要结论是，绳索效应力应在标准中作为多个变量的函数更详细地加以考虑，尤其是节点的位移。
