Application of Numerical Methods for Monitoring the Technical Condition of Cable Post-Tensioned Concrete Girders and Their Constituent Materials

Cable post-tensioned concrete roof girders constructed in Poland from the 1950s to the 1970s remain in service despite concerns regarding the long-term durability of their prestressing cables. This study investigated the feasibility of using deflection monitoring supported by numerical modeling as an indirect diagnostic method for assessing the technical condition of cable post-tensioned concrete girders. A finite element model of a 24 m span KBOS-24 cable post-tensioned concrete girder assembled from precast segments was developed and verified against in situ tachymetric measurements performed on existing girders in operating industrial facilities. Numerical simulations were conducted to evaluate the effects of complete loss of prestressing force in individual cables and thermal actions on girder deflection. Complete loss of prestressing force in one cable increased the deflection by approximately 2.5–4.0 mm. Temperature differences between the top and bottom chords produced deflections of comparable magnitude, reaching approximately 4.5 mm under the observed service conditions. The results indicate that long-term monitoring of girder deflections can provide valuable information on changes in prestressing cable condition, provided that thermal effects are simultaneously monitored and accounted for when interpreting the measurements.