New non-destructive dynamic tensile testing of prestressing fine-rolled screw-threaded steel bars

This paper presents a new non-destructive dynamic tensile test for fine-rolled screw-threaded steel bars (FSSBs) in prestressed concrete box-girder bridges. In this study, the anchorage nut and anchor plate are connected by a coupling spring, so are the steel bar and nut threads. A discrete dynamic model of a spring–mass system was therefore established to evaluate the bending vibration of the anchorage system. The tensile force in prestressing FSSBs can be determined indirectly using the measured natural frequency of the exposed section. Based on the force transmission characteristics of threads, a frequency correction equation is proposed to correct the test error in the tensile force. The laboratory model and field tests of multiple bridges show that the proposed test method for tensile force is feasible and practical. The proposed tension test method is rapid, non-destructive, and can be used repeatedly. It has no impact on the construction and offers potential wide applications. The study results are significant in terms of the testing and analysis of the induced tensions in mechanical components and similar structures of civil engineering.