DEVELOPMENT OF A PROBABILISTIC METHODOLOGY FOR ASSESSING THE ENVIRONMENTAL SAFETY OF A NATURAL-TECHNICAL SYSTEM BASED ON THE RELIABILITY INDEX β (CASE STUDY: THE VOLGOGRAD BRIDGE)

The study aims to justify the transition from deterministic methods of assessing the aeroelastic stability of long-span girder bridge structures to a probabilistic paradigm based on the reliability index β (ISO 2394) and stochastic simulation. The Volgogradsky Bridge across the Volga River, which experienced intense flutter-type aeroelastic oscillations with amplitudes up to 400 mm at a frequency of 0,42 Hz on May 20, 2010, was selected as the research object. The methods include physical experiments in a hydrodynamic tunnel with Karman vortex street visualization, mathematical simulation in ANSYS CFX using the Menter SST turbulence model, Strouhal number and critical velocity determination, and Monte Carlo probabilistic analysis. The Strouhal number was found to be Sh = 0,13–0,15, with resonance occurring at wind velocities of 13–15 m/s. Application of the reliability index β revealed a critical gap between deterministic (β_det) and stochastic (β_stoch) assessments, with Pf increasing from 0,39 % to 25,3 %. A BEE–β environmental safety matrix was developed, formalizing «greenwashing» and target stability zones. Investment in vibration dampers raises β to 4,5 with a 1:9 cost-effectiveness ratio.