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 pre-rig 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 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 as 80 by 100 feet on the east end and we didn’t want to jeopardize events that we already had on the books, but we knew we had to fit it in,” Davis reports. “We found a space of time where we had very few events that would use the grid and then we dropped it.”
The work started in June, continued in August and was completed in December.
One of the challenges was removing the “spider web” of cables that was holding the existing grid. That took a week. “There was a lot of demo,” Wells recalls. “One of the problems with this dome is that you had to rig off of the dome, and no two points were at the same elevation, because it’s a curved structure. So, there was a lot of cable that was just left hanging from the dome, I mean, hundreds of cables. It was a huge mess up there.”
The next step included taking down the grid, installing the brackets and rigging. The third phase, which was done over 10 days, was constructing and hanging the new grid. The final step was installing the fall protection lines and the bridges.
The final phase was completed right before Christmas. Davis admits the rush wasn’t so much about the holiday season as it was the desire to get it done as fast as possible. “The longer we went without it the fewer shows we could do and the less opportunity we had to have different concerts coming in,” she says. “It was costing us money not to have it, because we didn’t want to impact the artists.”
The advantages of this grid are many, Wells says. “First of all, they have a completely level, flat grid that’s trimmed out at 85 feet. That’s going to provide them with more than enough headroom for any show that comes into that building,” he says. “Then the access — to be able to walk up a stairway out onto the grid and immediately start dropping lines, with the right crew you could rig 200 points in one day. A 200 point show before would take four days of rigging and they would have had to rent the boom buckets and those are expensive.”
Indeed, Davis points out that the venue has already felt the positive impact of the install. “We’ve had a couple of events that would have had points coming off our old grid,” she explains. “We had a Strike Force Mixed Martial Arts event that was in the round and I don’t know if we would have done it as well without the new grid. One of the ways we were able to book Celine Dion for October was to guarantee that it would be in.”
This, Davis says, is the first part of the venue’s upgrades. In fact, by April they will be upgrading the curtains, trusses and motors. “We are a 22,000 seat building and we want to be able to go down to 5,000 seats,” she says. “With the curtains, trusses and motors we’ll be able to close off the upper deck as one piece and have a curtain backdrop.
