Analysis of failures of guardrail base-plates in scissors crossovers of the Athens Metro: The role of foundation–structure interaction

Connecting parallel rail tracks, scissors crossovers typically consist of four turnouts and a central diamond crossing, while flange-way gaps provide wheel flange clearance at the points of rail intersection. Guardrails, supported through base-plates, provide wheel guidance in the area of the gap. In the Athens Metro, within less than a year in operation, fracturing of a vast number of guardrail support base-plates was reported. This paper documents the methodology and results of a comprehensive investigation of the possible causes of these failures. This premature cracking was initially investigated through stress and acceleration measurements. Subsequently, a three-dimensional finite element model was developed to analyse the dynamic behaviour of the system with and without foundation deficiencies. It was unveiled that only the model with foundation deficiencies could reproduce the measured response. The role of foundation–structure interaction (FSI) proved doubly detrimental for the performance of the system: (i) the initial defective curved shape of the sleepers induced large bending pre-stress on the base-plates, and (ii) the defective gap-dominated foundation increased the flexibility of the system leading to further excessive sleeper bending, and thereby to increased distress of the base-plates. The combination of the two deficiencies was deemed responsible for the observed failure. The method of installation was shown to be of critical importance for the durability of the crossover.