Ultimate strength of deck grillages recovered from a decommissioned warship

Abstract

Cyclic ultimate strength testing of four deck grillage structures recovered from a decommissioned naval destroyer was conducted at Naval Surface Warfare Center Carderock Division to explore the behavior of in-service ship structure and generate data for modeling and simulation comparisons. The test articles spanned 3 or 4 complete frame bays of the original structure and included features typical of ship construction such as non-uniform thickness and frame spacing, hatch openings, and weld seams. Prior to strength testing, thickness and shape measurements were conducted on all test specimens, including full LiDAR scanning, and material properties were measured from coupons recovered from each grillage. Measured ultimate strength, post-collapse strength, load-shortening response collapse mode and location are compared with nonlinear FEA and Smith's method predictions. Numerical assessments were performed in two modelling configurations: nominal configuration, using design scantlings and material properties; and the actual configuration, using all pre-test measured data. Nonlinear FEA predictions indicate interframe collapse modes in a central frame bay, consistent with the test results, although differences in the collapse location and collapse mode of individual stiffeners are observed. Prediction of ultimate and post-collapse strength is shown to be greatly improved in the actual configuration, in particular when using measured material properties. Agreement between predictions and measured ultimate strengths is good, and Smith's method strength predictions are found to be comparable to FEA predictions.