Inelastic Dynamic Finite-Element Design of Bollard Systems to

Anti-Ram Barrier systems require foundations that are able to develop sufficient stiffness and strength in order to resist the specified vehicle impact. Although the performance of these systems is traditionally evaluated using tested assemblies and equivalent static force and energy methods, the limited test data and simplified engineering methods result in uncertainty and uneconomical design. Furthermore, these simplified methods do not take into account atypical site conditions, which may require modifications to standard details in order to avoid existing utilities and subsurface structures. However, dynamic inelastic analyses may also be used to determine the performance of these anti-ram systems in response to impact loading. These dynamic inelastic finite element analyses, which consider the interaction of the attack vehicle and the barrier system, accurately represents the potential failure mechanisms and provide the most accurate and economical design for anti-ram bollard systems. This paper will discuss the various subgrade conditions that limit the effectiveness of antiram barriers and the modifications to foundation designs that address these atypical conditions. This paper will describe the analytical methods that may be used to evaluate the performance of barrier systems in response to vehicle impact, including the advanced analytical methods that more accurately evaluate the system response. BACKGROUND Bollards were developed in order to stop a moving vehicle from approaching a building and thereby establish a “guaranteed standoff distance” between a building and a potential vehicle born explosion. If the bollards cannot stop the vehicle and the design threat penetrates the antiram perimeter, the design blast event will impose greater blast load on the building and cause a greater extent of damage. Therefore, it is critical that an anti-ram barrier performs as intended in order to properly protect the building. One of the leading developers of anti-ram barriers is the United States Government, Diplomatic Security (DS) division of the U.S. State Department and their earliest research was based on physical crash testing. The tests examine the importance of the size of foundation and the size of the barrier above ground. The sizes of these components are essential in providing the required strength and achieving the required performance. Strength and performance are two important characteristics in evaluating anti-ram systems. Anti-ram systems are required to resist the energy of the crash event. The height and spacing of these systems is critical in achieving the required performance. The center of mass of trucks and cars differs greatly and if the barrier is