Damage assessment of fixed U-shaped stiffeners stiffened square plates subjected to close-in explosions

The aim of this study is to suggest an approach for evaluating the damage modes and damage levels of the Ushaped stiffeners stiffened plates exposed to close-in explosions. To achieve this objective, a numerical model was developed in LS-DYNA, and the numerical model was verified by experimental results of the authors. Using this validated model, various U-shaped stiffeners stiffened plates were examined under different blast loads. The study investigated the factors that influence the damage modes of the plates, including the strength and distribution of the blast loads, as well as the geometry of the stiffened plates. The results indicated that the small size stiffened plates exhibited overall damage mode while the large stiffened plate showed localized damage at the same blast load. The blast load distribution on the different size plate led to different damage modes. Additionally, this study found that the slenderness of the stiffened plate had a great influence on the support rotation angle of the tensile tearing threshold. The larger span to thickness ratio can result in larger tensile tearing threshold. Moreover, 400 numerical cases were included and used to classify the damage modes of stiffened steel plates. Based on the damage mechanism of the stiffened steel plate, the damage number (Phi 1 and Phi 2) which considering the blast loads and material parameters of plate, the maximum incident angle of the blast load(alpha), and the relative stiffness of the stiffeners and the flat steel plate (kappa 1 and kappa 2), and the thickness to span ratio of the stiffened plate (lambda) were combined to identify the damage modes of stiffened plates. Furthermore, a flow chart was constructed for determining damage modes based on these considerations. Additionally, a curve surface fitting was performed using Phi 1 and lambda, the fitting formulas were then used to estimate the deformation characteristics of the stiffened plates with U-shaped stiffeners. The damage levels of the U-shaped stiffeners stiffened plates were then classified as low damage, medium damage, severe damage, and collapse by combining the nominal support rotation angle with the threshold of the global tensile tearing at boundaries. The study result can provide insight into the damage mode identification and damage level classification of stiffened steel plates under explosion. Additionally, this study was a base of damage evaluation of the structure elements (such as steel box girder) include stiffened steel plates under explosions.