Video photogrammetry for dimensional measurement and construction period estimation of post-tensioned PCT girder bridges lacking original records

There are significant maintenance challenges worldwide due to deteriorating bridge infrastructure and the lack of construction records. In the absence of original drawings, reconstruction designs must rely on external dimensions and period-specific standards, as these are necessary to determine the internal configuration of the structure, including the placement of reinforcing bars. The main objective of this study is to present and validate a workflow that estimates the construction year range from cross-sectional dimensions obtained by Structure-from-Motion (SfM) photogrammetry. Optimal imaging parameters were first established through controlled experiments on a concrete laboratory specimen and a dismantled post-tensioned prestressed concrete T-shaped (PCT) girder. These parameters were then applied to field surveys of five in-service PCT girder bridges managed by a Japanese municipal authority. Video-based SfM reduced field acquisition time by up to 83% compared with still-image SfM. Dimensional accuracy was within 3.6–4.8%, which is sufficient for restoration design. The measured cross-sectional dimensions were compared with historical Japanese design standard records. This comparison enabled correct identification of the applicable standard edition and construction year range for all five bridges. The framework has been validated for post-tensioned PCT girder bridges designed in accordance with Japanese standard cross-sectional dimension specifications.