North Carolina's coastal bridges are exposed to
storm surge, wave loading, and rising sea levels, yet previous statewide
guidance did not explicitly incorporate sea level rise and relied on older
wave-force methods.
This study developed and applied a screening-level
framework to evaluate the superstructure vulnerability of 116 selected Tier 1
and Tier 2 bridges in the state's 20 coastal counties. Structural parameters
were obtained from NCDOT records, roadway LiDAR, and available bridge plans.
Storm surge levels and significant wave heights were obtained from the U.S.
Army Corps of Engineers South Atlantic Coastal Study. Each bridge span was
evaluated under 15 scenarios consisting of 10-, 20-, 50-, 100-, and 500-year
storms under present-day sea level, 2.73 ft of sea level rise, and 7.35 ft of
sea level rise.
FHWA HEC-25 methods were used to calculate wave forces, and spans
were classified as Safe, Inundated, Uplifting, Sliding, or Rotation. A bridge
was classified as Vulnerable when at least one span was not Safe. Safe and
Vulnerable denote screening classifications for each evaluated scenario and do
not represent determinations of current structural safety or predictions of
damage or failure. Under the present-day 100-year scenario, 51 of 116 bridges
were classified as Vulnerable; this count increased to 68 under 2.73 ft of sea
level rise and 83 under 7.35 ft.
The 10-year scenario with a 2.73-ft sea level
rise resulted in approximately the same number of bridges classified as
Vulnerable as the present-day 100-year scenario, while the 10-year scenario with
a 7.35-ft sea level rise resulted in more bridges classified as Vulnerable than
the present-day 500-year scenario. Rotation was the most common force- or
moment-based dominant mode, and inundation became increasingly important as
water levels rose.
The study also developed the NC Coastal Bridge Vulnerability
Viewer, which combines mapping, querying, summary visualizations, and access to
bridge-specific results within a single interface.
