Road Test: Strong Technobeam, page 40 - PLSN.com

FEATURE
PROJECTION LIGHTS & STAGING NEWS
The Tacoma Dome truss grid measures 400 by 160 feet, with over
275 rigging points and a truss grid capacity of 625,000 pounds.
wooden wonder meets a mass of metal
The Tacoma Dome’s new super grid is called one of the largest suspended aluminum structures in the world
By DavidJohnFarinella
At 530 feet in diameter and 152 feet tall,
the Tacoma Dome is one of the world’s
largest wooden domed structures. For
the past 25 years, it has been the hub of entertainment
in the city, with events ranging
from music concerts to freestyle motocross
taking place here. Yet the Dome’s management
team started to feel the pinch of competition
coming from Key Arena in Seattle,
White River Amphitheater in Auburn and Everett
Event Center.
The Dome’s management team discovered
that the more popular acts were heading
to the other venues in part because of
production expenses, reports Tacoma Dome
Operations Manager Cynthia Davis. “For us to
do a concert in the round it would take a prerig
day, plus between two and four 125-foot
boom lifts, which are expensive. So, for us
to be more competitive to get those bigger
shows, we had to make it a lot more cost effective
and a lot more user friendly,” she says.
They also made it impressive. In fact, the
newly installed Tacoma Dome truss grid is a
whopping 400 by 160 feet with over 275 rigging
points and 750 bridle legs that enable a maximum
truss grid capacity of 625,000 pounds. The
grid is capable of supporting a 2-ton motor at
any location, and with a trim height of 85 feet 3
inches, there’s plenty of headroom.
“We believe this is the largest suspended
aluminum structure in the world,” Davis states.
“We wanted to go bigger. We wanted to go
wider so that it covered as much of the floor
as we could, but because of the slope of the
building and the weight of the grid, it wasn’t
possible. So, this was the cut down version.”
The first step in bolstering the grid was
taken in 2006 when the Dome’s management
team reached out to the original engineering
firm to see if the wooden roof structure could
support the additional load. When the word
came back that it was possible, a bid request
was put out. “We didn’t have any successful
bidders,” Davis reports. “Nobody seemed to
want to do the whole thing, which was the
hub upgrades, the construction of the grid
and the hang. So, we broke it up into pieces.”
That seemed to catch some companies’
attention, including Xtreme Structures & Fabrication
in Emory, Texas and Athletic & Performance
Rigging in Tiffin, Ohio. By the end
of the project, Davis explains, there were 10
different companies involved in the project,
including Atlanta Rigging Systems, Entertainment
Structures Group, Woodland Structures,
PCS Structural and Western Wood Structures.
Xtreme won the bid to build the massive
grid. In the end, it took three months
of 50- to 60-hour weeks to build over 500
truss components, primarily 24-by-20.5 inch
plated truss. That’s more than 8,100 linear
feet of truss. The job consumed over 114,000
pounds of aluminum, more than 15 miles
worth of aluminum tubes and plates and
two and a half miles of welds.
Delivering the truss was as much of a challenge
as building it. “They wanted to take delivery
all at once and so we had to rent a whole
separate building just to store it,” Mike Wells,
CEO of Xtreme Structures and Fabrication,
reports. “It took 5,000 square foot of storage
space just to stand the trusses up on end and
get them out of the way. When we shipped, it
was 12 completely full trucks of truss.”
Xtreme hired Entertainment Structures
Group as their specialty engineer. ESG Project
Engineer Jeff Reder was impressed by the
size of the job and points out that working in
a wooden dome was one of the more unique
aspects of the job. “These structures behave
quite differently than a typical building system,”
he says. “There was a lot of coordination
involved between ESG, Xtreme and the building’s
structural engineer as to the lateral bracing
scheme and how the grid structure hangs
from the dome.”
The grid was built out of aluminum, Wells
says, primarily because of the weight issue.
“Aluminum costs more than steel and it’s not
as strong as steel, but the weight is a huge
factor in a wooden dome structure that is
sensitive to what’s hanging off of it,” he says.
“To go in and hang a steel truss, which would
have weighed three times as much, would
have absorbed all of the dome’s capacity. So,
in this case, aluminum was mandatory.”
The grid is unique on a number of fronts,
according to Wells. A plated catwalk was
placed on top of the grid so a rigger can get to
the truss, connect into the fall protection line
and then walk the catwalk to get to any point
on the grid. “There are four access points,”
Wells explains, “one in each corner. We have
catwalk bridges that go between the grid and
the existing catwalk system in the Dome.”
The new catwalk bridges are independent
of the existing wooden catwalk system,
he adds.
The bridles are attached to the wood
beams via 300 or so U-shaped steel brackets
One of the first tasks was to install over 250 steel brackets to the
existing wooden structure to support the aluminum grid.
that slip around the beam and are secured via
12-by-1-inch thick steel bolts. Wells says there
were 1,200 holes drilled during the process.
Xtreme supplied the steel brackets that
attached to the beams and the truss, while
Athletic Performance Rigging and Atlanta
Rigging Systems put together the cables
and the bridles.
While the engineering and fabrication
teams were steaming ahead, the Tacoma
Dome management folks were finding the
time on the schedule to get the install done.
“We had a grid in the building. It was as small
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PLSN MARCH 2008