Title:
Long-Term Field Monitoring and Analysis of Post-Tensioned Flat Slab System (Prepublished)
Author(s):
Kwanwoo Yi, Ah Sir Cho, and Thomas H.-K. Kang
Publication:
Structural Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
deflection; long-term monitoring; optical fiber; prestressed concrete; prestress loss; smart tendon; unbonded post-tensioned concrete flat slab
DOI:
10.14359/51749492
Date:
1/19/2026
Abstract:
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 five 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.