Damage Identification For Joint Of Grid Structure Based On Piezoelectric Guided Waves

In the past decades,grid structures have been widely used as an important structure form in large-span civil and industrial buildings because of its good integrity,large spatial rigidity,stable structure and fast construction.Space grid structure has properties of being lightweight,covering a variety of shapes of the plane,being designed into a variety of.body shape,to meet the requirements of a variety of civil structures.Due to loading effect,environment actions,disaster impact,human activities etc,grid structures might generate bolt looseness phenomenon in their service period,resulting in decrease of reliability,may lead to destruction of the whole structure.Once these accidents happened,they will bring huge loss of human lives and properties.Therefore,it is valuable to develop early damage identification for grid structures,finding structural damage and performance degradation in the early stage,searching an effective way to identify nondestructive damage detection,taking timely remedial measures to eliminate potential safety problems.It is of great importance for the bolt looseness phenomenon of grid structures to be monitored by using piezoelectric effects of piezoelectric ceramics and combining with the method of detection wave energy,to find latent problems and take appropriate precautionary measures.This dissertation researches on non-defective grid structures and cracked grid structures through the combining method of the theoretical analysis,numerical simulation and experimental verification.The goal of the paper is to propose a method for evaluation of detecting the bolt-sphere joint looseness of grid structures.The different grid structures in the existing connection mode are firstly classified in the paper and a typical connection form is selected for research.A single sphere joint experimental model is established and three kinds of cases which the connection angles are 45°,90°,and 180°,respectively,are taken into account.Then,the multi-sphere joint damage tests by selecting six kinds of cases for multi-sphere joints are performed.Finally,the damage test of the whole grid is carried out.The piezoelectric ceramic patch array pasted on the surface of grid members is used as transducers to generate and receive detecting ultrasonic waves.The ultrasonic guided waves technology is applied by considering the grid structure joint as a black box,to overcome the difficulty of non-uniformity and nonlinearity of bolt-sphere joint interface during the detecting.The experimental results show that the ultrasonic wave propagation in the bolt-sphere joint and the bolt looseness impact on the ultrasonic wave energy attenuation have the certain regularity.Based on the relationship between the bolt looseness torque and the monitoring wave energy,an evaluation method and key techniques for bolt-sphere damage estimation based on ultrasonic wave energy are proposed and experimentally validated.Finally,based on the method of detection wave energy,using ABAQUS software,a single sphere joint is numerically simulated.Through the simulation results compared with the test results,it is concluded that the two basic results match well,verifying the feasibility and accuracy of numerical simulation and experimental method.