Abstract:
"Limiting Impact Force Due to Yielding and Buckling of the Plates and Internal Structural Frame at the Bow of a Barge during Its Headon Impact with a Bullnose or Cellular Structure"
This report details a research study that used finite element analysis to predict impact forces resulting from head-on collisions between a barge train and circular structures like bullnoses and cellular structures at the ends of lock approach walls. A detailed finite element model of the bow of a jumbo open-hopper barge was created using the mesh generation software TrueGRID. The model consisted of 357,897 nodes and 353,646 fully integrated LS-DYNA shell elements, representing the barge's deck, hull plates, and internal structural trusses. LS-DYNA was then used to perform 12 impact simulations, varying the bullnose diameter (20, 35, and 50 ft), the approach velocity (2 and 6 ft/sec), and the point of first contact (barge center line or in line with a truss). The model utilized a nonlinear elastic-plastic constitutive model for A-36 steel, with a large-displacement and large-strain formulation. A key finding from the nonlinear finite element analyses was the existence of a "capping force," where the force transferred to the impacted structure peaks and then decreases as the barge bow's plates and internal framing yield and buckle, effectively acting as a "structural fuseplug." The peak force values ranged from 2054 to 2836 kips, with the magnitude found to be proportional to the diameter of the impacted structure and dependent on whether the impact occurred at the center of the bow or in line with a structural truss. The study also compared its results with a previous finite element model and the AASHTO specification for impact force, finding that the LS-DYNA analysis of Case 1 predicted a permanent deformation smaller than what the AASHTO specification would for an equivalent amount of impact energy. Additionally, the LS-DYNA model showed that the impact force peaks and then decreases due to structural yielding and buckling, which contrasts with the AASHTO specification where force always increases with crush depth. This research provides a basis for establishing the capping force, which can be a valuable design consideration for bullnose and cellular structures.
