Book 1 - City of St. Petersburg

BASIS OF DESIGN BOOK 1
3 GENERAL PLANNING CRITERIA
ENGINEERING CRITERIA
(continued)
Wind and Wave Load Criteria
Wind loads for the new Pier shall be calculated based on ASCE
7-10 standard utilizing Risk Category II and Exposure D. This
results in a maximum wind load of 141 psf at the top of the
Canopy and 127 psf at the lower, more horizontal sections.
Due to the unique shape and response characteristics of the
structure, wind tunnel analysis will be required to determine the
wind pressure more accurately. Analysis of wind direction and
speed is necessary to determine dominant wind-generated wave
heights and direction. Moffatt & Nichol provided an Extreme
Value Analysis of historical wind speeds at MacDill Air Force Base
from 1941 through 2011 in their report entitled ‘St. Petersburg
Pier Design Competition Metocean and Structural Concept
Level Design Basis’. It was reported that the majority of wind
comes from the east-north east with winds in excess of 30 mph
occurring in some instance in all directions. This is attributable to
the passing of hurricane or tropical storm events. Return periods
for the 25, 50 and 100-year events found 10 minute wind speeds
of 74, 83 and 92 mph, respectively. However, these values did not
take into account wind direction and therefore the recurrence of
directional extreme winds should be analyzed for final design.
Waves found in Tampa Bay are either locally generated wind
waves or offshore swells that enter the Bay from the inlets
between Mullet, Egmont, Passage, and School Keys. Locally
generated wind waves are the dominant waves that are expected
to be found at the proposed Pier location. Design wave heights
shall be calculated to include storm surge as this will occur
during significant storm events.
Storm Load Criteria
The Pier approach and Pier head are located in a Coastal High
Hazard Area and designated a Velocity Zone (VE). The BFE is at 8
ft. The Pier is located in a VE-8 flood zone.
June through November is hurricane season in the Atlantic
Ocean and Caribbean Sea with the majority of hurricane activity
occurring between August and October. Tampa Bay experiences
effects of passing storms, although it is uncommon for the area
to receive a direct hit. The effect of these passing storms typically
result with high winds, increased wave heights, flooding due to
storm surge and increased cross-shore sediment transportation
rates. The 25 October 1921 “Tarpon Springs” storm was the last
major hurricane to directly hit the St. Petersburg area with wind
speeds of approximately 115 mph at landfall.
Hurricanes and tropical storms consist of large wind fields
driven by pressure gradients from a central low pressure and
temperature gradients in the atmosphere. The winds from these
events create storm surges by blowing the ocean water up
against the coastline. Flooding results from a combination of a
storm or tidal surge and high river stages from heavy rain. The
severity of flooding is dependent upon the intensity of the storm
event and its duration.
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THE NEW ST. PETERSBURG PIER