Analysis Of Crashworthiness And Design Improvement Of The Balsi-Beam Mobile Barrier System

The Balsi-Beam is a mobile barrier system currently used on California highways. In an accident event of a collision of an erratic vehicle into the barrier, the Balsi-Beam system should be able to contain and redirect the impacting vehicle to protect workers in the work-zone and also reduce the danger to occupants of the impacting vehicle and to other traffic.;The objective of this study is to investigate potential improvements to the crashworthiness of the Balsi-Beam system if layers of energy absorbing material are added to the outside barriers. Low density, closed-cell polyurethane foam is proposed for the application, because of its special mechanical characteristics. In efforts to simulate the oblique collision events of the modified Balsi-Beam system, it is necessary to select an appropriate constitutive model to represent polyurethane foam by evaluating the model against test data from similar loading conditions.;Simulations are conducted, using a finite element code LS-DYNA, at impact angles of 25°, 35° and 45°, for initial velocities of the impacting vehicle of 50, 70, 80, and 100 km/h (31, 43, 50, and 62 mph). The simulations indicate quantitatively that a layer of foam will enhance the purpose of the Balsi-Beam system to protect workers and drivers of other vehicles, by increasing both energy absorption and impact duration. However, the design modification results in higher decelerations of the impacting vehicle, which could increase injuries to the occupants of that vehicle. Further calculations to quantify the effects of the higher decelerations should explicitly model the occupants, seat belts, and airbags, which was beyond the scope of this study.;The effect of foam density on the dynamic behavior of the Balsi-Beam system is also studied for a subset of the cases. The general trend is that, compared to higher density foam, the low-density (5 lb/ft3) foam impact limiters used in the parametric study of collision velocity and impact angle result in lower exit velocity of the crashing truck without a significant increase in the mid-length normal-direction displacement of the Balsi-Beam system.;The effect of triggering dents on the impact limiters was also investigated for a subset of the cases. Comparison of the collision cases with and without triggering dents showed that the dents do not have a significant effect on the exit velocity of the colliding vehicle or the mid-length normal-direction displacement of the Balsi-Beam system.;In oblique collisions, normal forces are independent from tangential motions. However tangential forces are coupled with the normal forces. In the original Balsi-Beam design, the Coulomb Friction Law prevails at the sliding contact surfaces. In the modified Balsi-Beam design with foam impact limiters, the Coulomb Friction Law does not have a dominant contribution to the tangential force, because a wedge in the soft material at the contact zone changes the sliding contact problem to a growth contact problem. The effectiveness of the proposed foam layer to change the dynamic behavior in the contact zone is illustrated by changes in the coefficients of restitution (COR) which are reduced from 0.24 to 0.10 in the normal direction and from -1.0 to -0.13 in the tangential direction, for the case of 70 km/h initial velocity and 25° impact angle.