Fatigue Crack Propagation Behaviour of Steel Recovered from the Old Botlek Bridge

Abstract

The reuse of recovered materials plays an increasingly significant role in improving sustainability in the construction industry. For safe reuse, a detailed understanding of material behaviour is essential. The Old Botlek Bridge in Rotterdam was dismantled in 2017, and this study investigated the fatigue properties of the steel recovered from its main girders. The objective was to determine the fatigue crack growth parameters of the recovered steel using linear elastic fracture mechanics and the Paris–Erdogan equation.

Results from eleven SENB specimens tested under high-cycle fatigue loading at a nominal stress ratio of R = 0.1 were evaluated. Crack propagation was monitored using a crack gauge, a crack opening displacement gauge, and a strain gauge. A semi-automatic algorithm was developed to extract the crack-gauge wire-breakage points from the measured voltage signal. Crack lengths were inferred from the crack-opening displacement and strain measurements using calibrations obtained from two-dimensional finite element models. Crack growth rates were calculated using seven-point local polynomial differentiation for the crack-gauge data and neural-network regression with automatic differentiation for the COD- and strain-gauge-based data. The finite element models used linear-elastic material behaviour and mainly a geometrically linear formulation, while a geometrically nonlinear formulation was also applied as a sensitivity study. Stress intensity factors were extracted using contour integrals. The experimental crack growth rates were then combined with the specimen-specific stress intensity factor ranges to determine the Paris-law parameters.

All three measurement methods captured the same general crack growth trend. The calculated crack growth rates ranged from approximately 10⁻⁵ to 10⁻³ mm/cycle, but the three methods gave different results for the same specimen during the same experiment. Based on the specimen-balanced pooled results from the geometrically linear formulation, the crack-gauge-based evaluation gave m = 4.062 and C = 3.50 × 10⁻¹⁰, the COD-based evaluation gave m = 4.109 and C = 1.71 × 10⁻¹⁰, and the strain-gauge-based evaluation gave m = 3.618 and C = 8.93 × 10⁻¹⁰. These values apply within the method-specific fitting ranges, with da/dN expressed in mm/cycle and ΔK in MPa√m. The geometrically linear stress intensity factor results showed close agreement with the Baratta and Fett reference solution, with a mean absolute difference of 0.21% and a maximum absolute difference of 0.44%. The difference between the geometrically linear and nonlinear results increased towards larger crack lengths, showing that geometrical nonlinearity can affect the stress intensity factor in the final stage of crack propagation.

These differences show why the complete measurement and post-processing procedure must be reported alongside fatigue crack growth results and considered when comparing them. Over the common range of ΔK = 20–40 MPa√m, all three Old Botlek Bridge Paris-law curves were positioned above the selected literature curves for S235 J2, S355 J2, and old crane steel. The evaluated specimens therefore showed higher crack growth rates at the same ΔK and lower apparent fatigue crack-growth resistance. However, this difference cannot be attributed exclusively to the previous service history of the bridge steel because unused reference specimens from the same steel were not available.