LIGHTWEIGHT SOLAR CANOPIES WILL SHADE FLORIDA PEDESTRIAN BRIDGE
The design has
been completed for a pedestrian bridge in Tallahassee, Florida, that will be
lit by energy captured from suspended fabric solar cells.
The
capital city of the Sunshine State will soon have its very own solar-powered
pedestrian bridge. The $2.5-million Capital Cascades Connector Bridge in
Tallahassee, Florida, has been completed by a design team led by the
Tallahassee-based bridge engineering firm FIGG. Angled posts that will hold the
deck of the bridge will also support the flexible fabric canopies that appear
to flit across the top of the bridge, offering shade to those who pass beneath
and generating power above via integrated solar panels. The panels are expected
to gather enough energy to power the bridge's nighttime lighting, while excess
energy will be passed back to the energy grid.
"This
new signature bridge is an example that shows that aesthetic, form, and
function can be achieved simultaneously," says Linda Figg, M.ASCE, the
president and chief executive officer of FIGG. Figg served as the visual
quality and sustainability manager for the bridge and led a charette process
through which the community selected the bridge design from various options
prepared by FIGG.
The bridge is part of
the Capital Cascades Trail, a 4 mi project that will provide a multiuse
recreation trail and park within the city, according to Figg. "The
Connector Bridge is a modern concrete bridge with organic shaping based on a
theme of canopies and ecofriendly design inspired by the iconic canopy roads
that are part of Tallahassee, Florida's, unique landscape," she notes.
"The bridge deck creates a slender, uniform ribbon from end to end,
supported by a series of circular posts positioned at angles."
A 72 ft 6 in. main span
will extend across four lanes of traffic, while two side spans—one measuring 13
ft 9 inch. in length and the other 30 ft—will connect the bridge to the park on
either side of the main span. The bridge is approximately 13 ft 10 in. wide
with a full 12 ft available curb to curb so that pedestrians and bicyclists can
cross comfortably.
The
bridge is founded on rectangular concrete footings that are supported by 24 in.
steel pipe piles, according to Figg. The piles are mechanically connected to
the main footings, which support the bridge's angled substructure posts, which
hold both the deck and the canopies.
The 24 in. diameter
angled, steel substructure posts will be finished with a white powder coating
for aesthetic value, and will vary in length between approximately 25 and 42
ft. They will be filled with reinforced concrete to increase their stiffness,
according to Figg. "The canopies will connect at the top of each post,
which are oriented in different angles in the longitudinal direction of the
bridge and have a constant inclination angle in the transverse direction.
New
York City-based Pvilion, a vertically integrated solar design and manufacturing
company, created the fabric canopies that will top the bridge. The firm has
been involved in the project from the design engineering phase and will
continue to be involved all the way through manufacturing and installation,
according to Colin Touhey, the chief executive officer of Pvilion.
"For this project,
FIGG has designed the idea of solar tensile structures on a pedestrian bridge
and came to us early on in their design process so that we could help
incorporate our technology into the project," notes Todd Dalland, the
president of Pvilion.
"This isn't
something that flaps in the wind like a shade canopy you might see in the
backyard of someone's house," Touhey notes. "These are really
engineered like buildings." The canopies are engineered to protect against
the same wind loads called for in building codes as the permanent structures in
the area, according to Dalland.
To
create the canopies, a three-dimensional, digital, structural model was
developed to include all of the forces acting on the canopies, according to
Figg. This included the finished installation, as well as the forces that would
be present on the fabric during the installation and stressing of the cables.
"Moment, shear, and stresses were computed for all the structural members
and connections.
Overall,
flexible solar fabric canopies are a lighter-weight material than traditional
construction materials and are quicker to install, according to Touhey.
"All of our projects come sort of plug-and-play….We do all the work, and
then you basically put this thing up and plug it in. It doesn't require
tremendous amounts of wiring on-site," he notes. In addition to the ease
of installing solar such canopies , which can be used on the facades of
buildings, as well as rooftops, the cost is comparable to other construction
material, Touhey notes.
The solar fabric used in
the pedestrian bridge will be coated with a polyvinyl fluoride film so that it
can be largely self-cleaning in the rain, according to Pvilion.
The
bridge is expected to be built within 12 months.
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