A case study on strain gauge measurements on large post-tensioned concrete beams of a railway support structure

Non-destructive testing by means of strain gauges may be a straightforward operation under laboratory conditions. When applied on a construction site it becomes a wholly different matter This paper is concerned with the use of strain gauges as a control mechanism on the effectiveness of the post-tensioning of large concrete beams, used as part of the roof of a cut-and-cover tunnel for the high-speed train link passing under the Antwerp Central Station. The emphasis of this paper is placed on the practical execution of the measurements and the specific problems encountered when working on site. To validate the method used, a comparison is made between calculated and measured values of concrete stresses caused by the tensioning operations, proving that the measuring method is more than adequate. This case study shows the usefulness of strain gauges applied to the surface of concrete beams, as a practical, fast and accurate way of performing non-destructive strain measurements on major construction sites for civil engineering projects.