Design Challenges of Foundations for Coastal Cantilevered Highway Signs under High Wind Loads-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines foundation failures of coastal cantilevered highway signs under extreme wind loads, motivated by damage observed in Puerto Rico after Hurricane Maria in 2017. Two sign structures experienced substantial rotation and foundation failure.<br /><br />A North Carolina Department of Transportation–funded state-of-practice study reviewed literature and surveyed coastal U.S. transportation agencies. Drilled shafts were the predominant foundation type reported, typically ranging from 2–5 ft in diameter and 5–25 ft deep. Agencies use differing wind codes, design speeds, and analysis procedures, reflecting changes in standards and regional exposure.<br /><br />The central design challenge is that current practice generally analyzes lateral and torsional resistance separately, using simplified, decoupled methods. These approaches may not capture complex wind histories, soil–structure interaction, soil gap formation, cyclic degradation, or the interaction between torsion and lateral loading. Research findings cited in the presentation indicate that torsion can significantly reduce lateral capacity, while some conventional methods may overestimate lateral resistance.<br /><br />The presentation concludes that torsion often governs drilled-shaft design, but existing torsional-capacity models are simplistic. More research is needed on coupled loading, cyclic effects, gap formation, the influence of construction slurries, and foundations in layered soil profiles. Improved methods are important for designing reliable sign foundations in coastal areas exposed to high winds.

Keywords

coastal highway signs

foundation failure

extreme wind loads

Hurricane Maria

drilled shafts

torsional resistance

lateral capacity

soil-structure interaction

cyclic degradation

coastal infrastructure