Overview : Barge Impact loading of Infrastructure Systems
For infrastructure systems that are located in and around navigable waterways, the possibility of impact (collision) by cargo vessels e.g. barges is a critical loading condition that must be considered in the structural design and assessment processes. For structures such as guide walls (near locks), fenders, and protective dolphins, barge impacts can be expected to occur on a routine basis as part of regular structural service. In contrast, for bridge structures (piers) and flood protection walls, barge impacts are infrequent events and are typically considered extreme-event loading conditions. However, regardless of whether the impact conditions under consideration are classified as routine or extreme, the forces generated and the dynamic response of impacted structures are of critical concern for engineers performing hazard assessment or designing new structures.
Engineering design codes do provide guidance for quantifying barge impact loads, but these codified load models are based on data from fairly limited studies conducted decades ago. Furthermore, existing design codes prescribe the use of static loading conditions that largely omit dynamic amplification effects and the associated increases in required structural capacity. Unfortunately, such omissions can potentially lead to unconservative structural designs.
To address such issues, research conducted by a partnership of the University of Florida Department of Civil and Coastal Engineering (UF), the Florida DOT (FDOT), and the US Army Corps of Engineers (USACE), has focused on the development of improved procedures for designing a wide range of civil infrastructure systems (bridge piers, guide walls, etc.) to resist barge impact loading conditions (both service level, and extreme event). Over the past 15 years, our team has conducted numerous research projects for the purpose of quantifying vessel impact loads, studying structural response to such loads, and developing improved analysis and design procedures.
In 2004, UF and FDOT conducted a one-of-a-kind experimental study in which a full-scale river barge was used to impact multiple piers of a decommissioned bridge near St. George Island, Florida. This study was one of only a few of its kind, employing a full-size barge in realistic field conditions, and it still is the only known full-scale instrumented study involving barges striking bridge piers. Results from the St. George Island impact experiments revealed important shortcomings in widely used bridge design specifications, and prompted the development of improved design procedures.
With ever increasing computing power, it has also become feasible to examine–in detail the dynamics of impact loading and structural response using numerical simulation methods such as finite element analysis. Our team has developed finite element models capable of simulating an entire barge flotilla (a collection of multiple interconnected barges), including key system intricacies ranging from severe crushing deformations and plate tearing to modeling wire rope lashing behavior with consideration of failure. Using very high-resolution finite element models (with up to approximately 1 million elements), our research group has conducted hundreds of nonlinear, dynamic impact simulations of barges striking bridge piers, hurricane protection structures, and waterway guidance structures (walls and bullnoses). Results from these simulations validated against available experimental data have provided new insights into the nature of vessel impact loads and structural responses. Using such information, structural design methodologies with improved safety and economy have been developed for infrastructure systems that are located near navigable waterways.