Operational Modal Analysis of Periodic Structures with Application to the Olifants River Viaduct

In recent decades, the dynamic investigation of periodic structures has been attracting a lot of attention worldwide. Periodically supported continuous beams have been among the most investigated structures, with focus on the free vibration analysis. In this paper, the dynamic behaviour of the 23-span, 1035 m-long, Olifants River Viaduct is investigated through ambient vibration tests (AVTs). The viaduct consists of two 11-span 495 m-long continuous posttensioned concrete (PC) girders and one 45 m-long simply supported PC beam located in between the two girders. The viaduct deck carries a ballasted continuous welded rail for heavy-haul railway operation which introduces some continuity between each girder and the central beam. The supports are periodically located and consist of two RC abutments and twenty-two RC piers 45 m apart. After a short introduction on the dynamic behaviour of periodically supported continuous beams, the investigation of the vertical modal behaviour of the viaduct, through operational modal analysis (OMA), is presented. Results are used as a basis to discuss the viaduct modal behaviour, compared to major finding in the literature, as well as the challenges arisen in the AVTs.