Statistical properties of the yield strength of normal strength hull structural steel plates

Résumé

The statistical properties were studied of normal strength hull structural steel plates (with a strength level of 235) of a thickness of  50 mm that were manufactured in 1990-1991 at four European steelworks. The study focused on the yield strength, as the available literary sources indicate that in terms of structural strength and design assessment this particular aspect is the most essential property of steel used for ship structures, and, at the same time, its values are characterized by the highest variability. Detailed statistical tests were performed on nearly 2,200 plates. The results of these analyses suggested that for the sample examined herein the mean yield strength value was 308.3 MPa, the standard deviation was 25.24 MPa, the coefficient of variation was 0.0819 (8.19%), the (average) difference bias was 73.3 MPa and the (average) ratio bias was 1.31. It has been shown that both lognormal distribution LN(5.7276, 0.0817) and normal distribution N(308.2589, 25.2444) provide an adequate representation of normal strength hull structural steel plates.