School of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China.
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, Liaoning, China.
Sensors (Basel). 2018 May 28;18(6):1727. doi: 10.3390/s18061727.
Bolted spherical joints are widely used to form space steel structures. The stiffness and load capacity of the structures are affected by the looseness of bolted spherical joint connections in the structures. The looseness of the connections, which can be caused by fabrication error, low modeling accuracy, and "false twist" in the installation process, may negatively impact the load capacity of the structure and even lead to severe accidents. Furthermore, it is difficult to detect bolted spherical joint connection looseness from the outside since the bolts connect spheres with rods together from the inside. Active sensing methods are proposed in this paper to monitor the tightness status of the bolted spherical connection using piezoceramic transducers. A triangle-on-triangle offset grid composed of bolted spherical joints and steel tube bars was fabricated as the specimen and was used to validate the active sensing methods. Lead Zirconate Titanate (PZT) patches were used as sensors and actuators to monitor the bolted spherical joint tightness status. One PZT patch mounted on the central bolted sphere at the upper chord was used as an actuator to generate a stress wave. Another PZT patch mounted on the bar was used as a sensor to detect the propagated waves through the bolted spherical connection. The looseness of the connection can impact the energy of the stress wave propagated through the connection. The wavelet packet analysis and time reversal (TR) method were used to quantify the energy of the transmitted signal between the PZT patches by which the tightness status of the connection can be detected. In order to verify the effectiveness, repeatability, and consistency of the proposed methods, the experiments were repeated six times in different bolted spherical connection positions. The experimental results showed that the wavelet packet analysis and TR method are effective in detecting the tightness status of the connections. The proposed active monitoring method using PZT transducers can monitor the tightness levels of bolted spherical joint connections efficiently and shows its potential to guarantee the safety of space steel structures in construction and service.
螺栓球节点被广泛应用于空间钢结构的搭建。结构的刚度和承载能力会受到螺栓球节点连接松动的影响。连接的松动可能是由制造误差、建模精度低以及安装过程中的“假扭转”等原因造成的，这可能会降低结构的承载能力，甚至导致严重的事故。此外，由于螺栓从内部将球体和杆件连接在一起，因此很难从外部检测到螺栓球节点连接的松动情况。本文提出了一种使用压电阻抗传感器监测螺栓球连接紧固状态的主动传感方法。制作了一个由螺栓球节点和钢管组成的三角形对三角形偏移网格作为试件，验证了主动传感方法。在试件中，将压电阻抗传感器和激励器粘贴在螺栓球节点上，使用一个粘贴在上弦中心螺栓球上的 PZT 贴片作为激励器，生成应力波，另一个粘贴在杆件上的 PZT 贴片作为传感器，检测通过螺栓球连接传播的波。连接的松动会影响通过连接传播的应力波的能量。使用小波包分析和时反（TR）方法对 PZT 贴片之间传输信号的能量进行量化，从而可以检测连接的紧固状态。为了验证所提出方法的有效性、可重复性和一致性，在不同的螺栓球连接位置重复进行了六次实验。实验结果表明，小波包分析和 TR 方法可有效检测连接的紧固状态。使用 PZT 传感器的主动监测方法可以高效地监测螺栓球节点连接的紧固程度，为保证空间钢结构在施工和使用中的安全性提供了一种潜在的方法。
