PSI - Issue 62

Giulia Rossini et al. / Procedia Structural Integrity 62 (2024) 347–354 Giulia Rossini et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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5. Conclusions This research focused on the application of three semi-destructive methods based on tension for in-situ prestressing evaluation. The results of the in situ tests and numerical analysis can be briefly summarized as follows: • These methods are rather delicate and, for the most part, operator-dependent. Consequently, accuracy and care in the preparation and execution of the test are essential. We should also keep in mind that the tests were carried out at the laboratory of the University of Brescia, thus with favorable environmental conditions. It is assumed that the performance of these tests presents additional limitations and problems if carried out in situ; • Successful testing requires very low level of porosity and the execution of an undisturbed cut, the latter being difficult to achieve, in actual bridge girders; • The Saw-Cut method – Web has proven to be a reliable approach, the most accurate among the semidestructive methods used in this experimental program. Not only it is easy to perform, using relatively inexpensive commercial tools, but with the configuration of parallel cuts 6 cm apart and 3 cm deep, it generates results that closely align with analytical and numerical predictions, providing conservative estimates. In fact, the actual prestress in the element is underestimated by 10 percent, with a coefficient of variation (CoV) of 21%. For this geometric configuration, the finite element model detects tensile stress in the area monitored with strain gauges between the two saw-cuts. This phenomenon can be attributed to arc-shaped distribution of compressive stresses that, through self-balancing, induce stresses at points on the surface between the two cuts that are no longer constrained. Further investigations are needed in this regard. Acknowledgements The study herein presented was carried out as part of the activities envisaged by the Agreement between the High Council of Public Works (CSLLPP) and the ReLUIS Consortium implementing Ministerial Decree 578/2020 and Ministerial Decree 240/2022. The contents of this paper represent the authors’ ideas and do not necessarily correspond to the official opinion and policies of CSLLPP. References ASTM E837-13a. (2013). Standard Test Method for Determining Residual Stresses by the Hole-Drilling Strain Gage Method. In Standard Test Method E837-13a (pp. 1 – 16). https://www.astm.org/e0837-20.html Azizinamini, A., Keeler, B. J., Rohde, J., & Mehrabi, A. B. (1996). Application of a new nondestructive evaluation technique to a 25-year-old prestressed concrete girder. In PCI Journal (Vol. 41, Issue 3, pp. 82 – 95). https://doi.org/10.15554/pcij.05011996.82.95 Bagge, N., Nilimaa, J., & Elfgren, L. (2017). In-situ methods to determine residual prestress forces in concrete bridges. Engineering Structures , 135 , 41 – 52. https://doi.org/10.1016/j.engstruct.2016.12.059 Chang, C. W., Chen, P. H., & Lien, H. S. (2009). Evaluation of residual stress in pre-stressed concrete material by digital image processing photoelastic coating and hole drilling method. Measurement: Journal of the International Measurement Confederation , 42 (4), 552 – 558. https://doi.org/10.1016/j.measurement.2008.10.004 Kesavan, K., Ravisankar, K., Parivallal, S., & Sreeshylam, P. (2005). Technique to assess the residual prestress in prestressed concrete members. Experimental Techniques , 29 (5), 33 – 38. https://doi.org/10.1111/j.1747 1567.2005.tb00238.x Khaled, T. (1999). Residual stress measurement by the hole drilling method . Kraľovanec, J., Bahleda, F., Prokop, J., Moravčík, M., & Neslušan, M. (2021). Verification of actual prestressing in existing pre-tensioned members. Applied Sciences (Switzerland) , 11 (13). https://doi.org/10.3390/app11135971 Kraľovanec, J., & Moravčík, M. (2021). Numerical verification of the saw -cut method. IOP Conference Series: Materials Science and Engineering , 1015 (1), 012031. https://doi.org/10.1088/1757-899x/1015/1/012031 Kraľovanec, J., Moravčík, M., Bujňáková, P., & Jošt, J. (2021). Indirect determination of residual prestressing force