Failure and repair analysis of a runway beam: Influence of the standard applied to lifetime prediction

• Failure of large runaway beams is analyzed.
• Non-adequate welded joints decrease significantly the life due to fatigue.
• Different standards are studied and applied for fatigue life prediction.
• Operational stresses are measured to obtain a more reliable loading spectrum.
• Different solutions to avoid stress concentrations in the beams are proposed.

The structural integrity of a welded structure is guaranteed insofar as the integrity of any particular welded detail is ensured. This is highlighted in this paper which analyzes the premature failure of a runway beam, occurring only two years after being commissioned. Initial fractographic analysis and visual in-situ inspection of the beam suggest that the failure was caused by fatigue. The fracture initiated in an apparently innocuous zone where the beam joins a twin runway beam, the bracing of which is performed by a transverse truss beam with fillet welds.The failure analysis was performed according to two standards specific to runway beam design: the former Spanish UNE 76202:1992 standard, applicable at the time the beam was built, and the current EN 1993-1-9:2005 standard. The main difference between the two standards consists in the load spectrum considered for calculations. While UNE 76202:1992 prescribes a defined combination of the most unfavorable loads, EN 1993-1-9:2005 leaves to the designer’s discretion the choice of more realistic load data directly derived from in-service observations or measurements, which presumably better reflect the loads the beam will have to support throughout its service life.To achieve this goal, once the beam was repaired and operating once again, in-service strain measurements were performed over several days. These measurements allowed us to obtain a real load spectrum, which was taken into consideration in fatigue strength assessment based on the EN 1993-1-9:2005 standard. The results provide a more realistic fatigue life prediction than that obtained using UNE 76202:1992, a standard no longer applicable.