International Concrete Abstracts Portal

This study presents a comprehensive field investigation into the long-term behavior of unbonded post-tensioned (PT) concrete flat slabs using Smart Strands embedded with fiber Bragg grating (FBG) sensors. The monitoring program was conducted in a real-world building in Seoul, Korea, spanning over 5 and a half years and capturing continuous prestressing force and deflection measurements at multiple slab locations. Results revealed that approximately 5% of nominal strength of tendon prestress losses occurred within the first year, stabilizing thereafter, and that deflection patterns were significantly influenced by slab position and construction activities. Comparison with analytical models showed strong alignment, with ACI CODE-318-25 time- dependent coefficients accurately predicting long-term deflections after the early-age period. This study contributes valuable long-term data, validating design codes and guidelines and enhancing understanding of the time-dependent behavior of PT concrete structures.

Prestressed concrete enables slender, economical, and durable structures, with post-tensioned (PT) precast girders widely used in bridge construction. Accurate design requires precise prediction of prestress losses, among which friction losses, arising from duct curvature, wobble, and anchorage slip, are most significant. Existing codes employ simplified exponential models, yet notable discrepancies persist between predicted and actual field values. This study presents full-scale experimental testing on PT precast girders used in Egypt’s Light Railway Transit (LRT) Project. Prestressing forces were measured using strain gauges to evaluate friction losses along tendon profiles. Results revealed that measured losses consistently exceeded code-based predictions, highlighting the influence of stress level and nonlinear variation along the tendon; factors often ignored by current provisions. Regression analysis yielded refined exponential models with improved accuracy and strong agreement with observations. The proposed refinements enhance predictive reliability and provide a foundation for updating design codes toward safer, more realistic PT concrete structures.

This study presents a real-time, automated monitoring system designed to enhance the constructability and execution of post-tensioned (PT) concrete construction by streamlining the measurement and verification of tendon force and elongation. The system integrates a pressure sensor, laser-based distance sensor, and data logger with embedded algorithms to correct for field-specific variables such as initial slack, wedge slip, and equipment irregularities. Designed with construction efficiency in mind, data is transmitted via mobile and web platforms, allowing real-time access for field crews and managers. Since its initial development, the system has been refined through multiple field applications. To validate its reliability and practical readiness, a large-scale field test involving 1,913 unbonded single-strand tendons across 28 construction sites was conducted. Results showed strong alignment with conventional tape measurements, with average deviations of 2.79% ± 2.34% for tendons longer than 12 m and further reduced to 2.04% ± 1.49% for those over 28 m. Comparisons with theoretical elongation confirmed that deviations remained within or below the ranges typically reported in field practice. The system's real-time monitoring was especially valuable in short tendon applications, where statistical variation is greater, helping identify and analyze potential quality issues. Reducing reliance on manual measurement, improving data transparency, and enabling rapid detection of issues such as hydraulic leaks or gauge drift, the system significantly boosts quality control, decision-making, and overall construction efficiency in PT operations.

Corrosion of prestressing steel can threaten the durability of prestressed concrete. To ensure the durability of unbonded post-tensioning (PT) systems, it is crucial to investigate the effects of construction defects such as grease leakage and high-density polyethylene (HDPE) sheath damage. This study quantified the thickness of grease coating (PT coating) and HDPE sheath damage as experimental variables. An accelerated corrosion test was conducted in two environments: 1) chloride ions only (Cl–); and 2) both chloride ions and dissolved oxygen (Cl– + DO). The corrosion current density and weight loss of prestressing strands and the suspended concentration density of corrosion cell solution were measured to quantify the corrosion performance. Increasing the grease coating thickness over 0.3 mm (0.012 in.) did not significantly enhance corrosion resistance. Realistic levels of HDPE sheath damage had no significant detrimental effects on durability; however, excessive HDPE sheath area loss must be avoided for long-term durability. It was examined to quantify the interrelationship between three data—electrochemical measurement, weight-loss, and suspended concentration density—as quantitative corrosion data. The findings of this study can serve as a basis for developing durability-related provisions, as well as controlling the construction defects of unbonded PT systems in field applications.

An approach to improve the progressive collapse resistance of conventional reinforced concrete (RC) frame structures was put forth by using unbonded post-tensioning strand (UPS). Two UPSs with straight profiles were mounted at the bottom of the beam section. A static loading test was conducted on an unbonded prestressed RC (UPRC) beam-column subassemblage under a column removal scenario. The structural behaviors of the test specimen such as load-carrying capacity, failure mode, post-tensioning force of the UPSs, and reinforcing bar strain were captured. By analyzing the results of the tested substructure, it was found that the compressive arch action (CAA) and catenary action (CTA) were sequentially mobilized in the UPRC subassemblage to avert its progressive collapse. The presence of UPSs could significantly improve the load-carrying capacity of conventional RC structures to defend against progressive collapse. Moreover, a high-fidelity finite element (FE) model of the test specimen was built using the software ABAQUS. The FE model was validated by experimental results in terms of the variation of vertical load, horizontal reaction force, and post-tensioning force of the UPSs against middle joint displacement (MJD). Finally, a theoretical model was proposed to evaluate the anti-progressive collapse capacities of UPRC subassemblages. It was validated by the test results as well as the FE models of the UPRC subassemblages, which were calibrated using the available experimental data.