Fatigue Life Assessment of a Steel Railway Bridge with Pot-PTFE Bearing

Fatigue is an important issue for the failure of steel railway bridges. It is very challenging for a railway industry to regularly monitor the fatigue safety of millions of steel railway bridges in a cost-effective and easy way requiring the least worker effort and software expertise. This case study presents the fatigue life assessment (FLA) of an existing railway bridge in a simple and easy way. Microsoft Excel (for calculation of limit states of failure and fatigue life) and STAAD.Pro or similar structural analysis software (for modeling of the bridge truss) was used. A total station was used to ascertain the actual behavior of the bridge and to derive a correction factor. The various limit states of normal and shear stresses and strains in truss members and pot–polytetrafluoroethylene (PTFE) bearing components are addressed in a single procedure. The accuracy of the method was validated using a case study of a failed railway bridge. LVDT-based deflection measurements showed the accuracy of the adopted total station instrument–based experimental program. To check the fatigue safety of the bearing components, available equations from the literature were used to make the procedure easy and quick. In addition, the accuracy of the equations was ensured through a detailed numerical modeling of pot-PTFE bearings using finite-element modeling in Ansys. The results show that among the various limit states of normal and shear stresses and strains in truss members and bearing components, the shearing strain limit state of the elastomeric pad of the pot-PTFE bearings governs the fatigue life, which often is disregarded in usual FLA. The results indicate that the adopted method is cost- and time-effective.

This case study presents a fatigue life assessment procedure executed on a real-life steel railway bridge. The procedure is quick, easy to implement, requires less funding and human effort, and can be used for many bridges. The adopted procedure requires only structural analysis software such as STAAD.Pro, MS Excel, and a total station surveying instrument. The total station surveying instrument is used to arrive at a corrected factor from the measured deflection values, which validates the analytical model of the steel bridge with the real-time behavior of the bridge at site. Skilled specialist human effort or software personnel with expertise in Ansys fatigue workbench, Abaqus, and UMAT interfaces are not required. The total station surveying–based approach quite accurately captured the failure of another real-life railway bridge, which failed in fatigue. The procedure is generic in nature and can be applied to other types of railway bridges with different types of bearings. The method can investigate the failure of stress- and strain-based fatigue failure of different bearing components and various limit states of truss or frame members in a single procedure in a computationally efficient way.