Case Analysis of Non-destructive Testing for Historical Timber Structures in Shanghai

Timber is one of the widely used construction materials in historical structures all over the world. After many years of use, defects such as decay, termite infestation, and cracking are quite common, and the strength is difficult to estimate. Non-destructive testing methods play an important role in the safety assessment and historic preservation. Several timber structural inspection projects of historical buildings in Shanghai are presented in this paper to demonstrate the application of non-destructive testing methods such as the drilling resistance method and the endoscopic method. The estimation of the timber strength grade is introduced and compared with the timber species. The feasibility of the detection methods is analysed based on the testing results. Analyses results indicate that the drilling resistance method can reasonably demonstrate the location and geometry of internal defects for timber structures of historical buildings. The resistance value of timber members after fire is measured by the drilling resistance method. The peak value of resistance curve of the slightly carbonized part decrease insignificantly, and the peak value of the severely carbonized part is significantly lower than that of the undamaged part. The amplitude of the resistance curve of the internal uncarbonized part was close to that of the undamaged part. The endoscopic method can reasonably characterize the internal damage of timber members and mortise and tenon joints, and the geometry details of mortise and tenon joints can be measured. The comprehensive ultrasonic-drilling resistance method is feasible in estimating the strength grade of timber. The research results can provide technical support for the non-destructive testing for historical timber structures.