Last month, a structural glass pedestrian bridge in a desert area collapsed without warning or apparent load. The forensic investigation, supported by 3D simulation, identified two concurrent causes: nickel sulfide micro-inclusions and an extreme thermal gradient. This article breaks down the technical workflow to determine the cumulative fatigue that exceeded the material's design limits.
Forensic workflow: Photogrammetry, deformation, and thermo-mechanics 🔍
The process began with capturing the fragments using Agisoft Metashape, generating a precise point cloud for the visual reconstruction of the fracture pattern. Subsequently, GOM Inspect analyzed residual deformations on the edges of the pieces, revealing concentric micro-cracks around black spots (NiS inclusions). Thermal simulation in Ansys Discovery modeled the desert day-night cycle, applying a 50-degree Celsius gradient between the upper and lower glass surfaces. The results showed that differential expansion, combined with localized stress from the inclusions, generated fatigue peaks that exceeded the breaking limit of the tempered glass.
Lessons for structural design in extreme environments 🏗️
This case underscores the need to validate construction materials with multiscale simulations that integrate real meteorological data. The use of glass with low nickel sulfide content or additional heat treatments could have prevented the failure. The combination of photogrammetry, deformation analysis, and thermal simulation is consolidating as the standard for structural accident investigation, allowing not only to determine the cause but also to propose improvements in design codes.
Is it possible to model, through finite element simulation, the synergistic interaction between an extreme thermal gradient and the expansion of nickel sulfide inclusions to predict the fracture pattern in a structural glass bridge?
(PS: Material fatigue is like yours after 10 hours of simulation.)