X-Ray Measure Of Tensile Force In Post-Tensioned Steel Cables

Non-Destructive Testing methods are key tools for the proper characterization of existing constructions and for their reliable structural assessment. Even if several sophisticated methods are currently available, the possibility of using them strongly depends on the analyzed structural typology. This is particularly true for some specific classes of structures like pre-stressed reinforced concrete ones, for which very few methods exist for the evaluation of the residual pre-stressing force in the elements. Moreover, most of them are currently under development, even if this is a crucial information for their structural analysis and assessment. The paper presents a new Non-Destructive Testing method based on the innovative application of X-ray diffraction for the assessment of the tensile force present in pre-stressing wires and strands. The method is firstly conceptualized considering the main features of the X-ray diffraction and the specific issues related to the geometry of the strands, such as the presence of intertwined spiral wires. The method is then formalized proposing a detailed procedure for the estimation of the total tensile force present in the pre-stressing wire or strand on the base of the X-ray diffractometer measurements and of the nominal geometrical and mechanical properties of the element. Finally, an extensive experimental campaign is used to assess the effectiveness of the proposed procedure. The results show the optimal agreement between the tensile force estimated by the proposed procedure and the one effectively applied and allow estimating the measurement error as a function of the tensile force. The in situ tests demonstrate the actual possibility of using the proposed method together with the issues to be still fixed or enhanced.