Vessel Collision Design – Risk Analysis and Deep Foundation Issues for Bridges over Navigable Waterways-PDF

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The paper reviews U.S. AASHTO requirements for assessing and designing bridges against vessel collisions, with emphasis on risks to bridge foundations. Historical disasters—including the Sunshine Skyway, Bayou Canot, Queen Isabella, and I-40 bridge collapses—show the potential for major loss of life, infrastructure damage, and environmental harm. A U.S. Coast Guard study found thousands of bridge collisions, most associated with human error.<br /><br />The 1991 AASHTO Guide Specification introduced a risk-based approach. Its principal method estimates annual collapse frequency from vessel traffic, the probability of a vessel losing control, the likelihood that it will strike a pier, and the probability that impact will cause collapse. Design criteria differ for “critical” and “regular” bridges. The guide also provides impact-force estimates and allows protection systems such as dolphins, fenders, and islands. Incorporating collision risk early in planning often favors longer spans with fewer exposed piers, while retrofitting protection can be very costly. Vessel-collision provisions later became mandatory in the AASHTO LRFD specifications.<br /><br />The paper identifies important uncertainties. AASHTO’s ship-impact forces are based on average forces, while European guidance uses higher maximum forces and dynamic amplification factors. Full-scale barge tests show that structural and soil stiffness affect collision forces and that dynamic responses may differ substantially from predictions using static loads. The codes also offer limited guidance on designing protection systems and combining collision loads with scour or other extreme events.<br /><br />For immediate improvements, the author recommends clarifying how pier protection, vessel length, water depth, and scour are treated in risk calculations. Longer-term priorities include research on ship and barge impact dynamics, consistent risk criteria across extreme events, practical design methods for protection systems, and quantifying the safety benefits of navigation aids. Overall, AASHTO provides a useful framework, but further research is needed to improve safety, reliability, and cost-effectiveness.

Keywords

AASHTO

bridge collision risk

vessel impact

bridge foundations

ship collisions

risk-based design

bridge protection systems

LRFD specifications

pier scour

dynamic impact forces