Book 1 - City of St. Petersburg

BASIS OF DESIGN BOOK 1
5 BASIS OF DESIGN CONCEPT ANALYSIS
ENGINEERING NARRATIVE
Marine Work
The design team has preliminarily identified potential supports
for the new Pier elements, which include new piles and caissons,
as well as selective reuse of the existing caissons supporting
the Inverted Pyramid building. Actual design of foundations
for the Pier will begin following execution of the geotechnical
exploration program and more precise site-specific evaluation of
wind and wave loads during the next stage of work. At this early
phase, the engineers believe the following foundation types
would be viable options:
• Overwater Drive – A three-pile pier system, with one
vertical and two batter piles supporting pile caps spaced
at approximately 60’, could support the roadway/
walkway. The pile type could be a precast 18” square
concrete pile driven into place.
• Overwater Bridge – Single large diameter (estimated at
48”) caissons spaced at 100’ could support the relatively
narrow structure. The caisson would be a steel shell
drilled into the bay bottom and filled with concrete.
• The Promontory, Lens Canopy, and related decking
would be supported by a series of pile caps custom
poured to match the varying horizontal surface area.
Again, precast 18” square piles could be used, although
some areas may need 20” piles, and the stair may use
drilled steel pipe piles with concrete fill. The design
team has examined reconfiguration of the Promontory
layout to engage the existing caissons presently
supporting the Inverted Pyramid building.
Structural Approach
The design team has preliminarily identified potential
superstructures for the new Pier elements. Actual design of
these structures will begin following a more precise site-specific
evaluation of wind and wave loads, but at this early phase, the
engineers believe the following superstructure types would be
viable options:
• Overwater Drive and Overwater Bridge – Precast beams
are appropriate for construction of what are essentially
bridges over water. The design team consulted the PCI
Manual and identified several standard shapes which
would function well for the 60’ span of the Overwater
Drive and the 100’ span of the Overwater Bridge. Precast
box beams and standard tees were sketched as options
for the structural concept plans. Further discussions led
by the Construction Manager revealed that Florida tee
beams and/or double tees could be more economical
due to local availability. Further investigation and design
will be conducted in the next design phase to select the
optimal precast beam shape. A concrete slab would be
placed atop the beams and extend past the edges of
the beam to form the full width of structure and support
the edge railings. The superstructures may receive a
cladding for aesthetic purposes.
5 - 2
THE NEW ST. PETERSBURG PIER