Four Seasons Resorts and Hotels, the world's premier hospitality company, offers experiences of exceptional quality. In addition to its luxurious hotels, the company offers branded vacation ownership properties and private residences, such as the new Four Seasons Resort Jackson Hole in Teton Village, Wyo. Four Seasons creates only properties of enduring value using superior design. So does Jackson-based Intermountain Erectors, which is responsible for structural steel construction on the new resort.
|
|
|
Fig. 1-Structural steel moment frames provide axial and lateral support for the residential structures at the Four Seasons Resort Jackson Hole.
|
As project manager for the job, Intermountain's Pete Henrie is particularly fussy about his welding equipment. He uses mostly machines from Miller Electric Mfg. Co. The welds are especially critical because the area's seismic activity rating matches that of San Francisco's. To "build a property of enduring value" demands using steel moment frames to support load-bearing walls.
"A steel moment frame carries the sheer part of the building to give it more axial (side-to-side) and lateral (up and down) support," says Henrie. Most easily seen on residential structures (Figure 1), the moment frame provides an anchor to which the wooden frame is attached via bolts welded to the frame (upper part of Figure 2).
|
|
|
Fig. 2-Welding operator Gary Wadsworth uses the Suitcase 12VS to make a butt weld on this steel moment frame.
|
Seismic Stability
The three-story private residences and three- and four-story main building at the Four Seasons Resort Jackson Hole rely on steel moment frames to ensure structural integrity. A moment frame consists of steel beams and columns joined by a combination of welding and bolting. They resist lateral loads through bending of the frame elements. In the case of minor seismic activity and wind loads, the elastic property of steel causes the frame to return to its original shape without any permanent deformation.
In the case of a major earthquake, the ductile properties of steel allow the frame to stretch and absorb energy. Permanent deformation of the steel-frame is expected, but the frame remains intact to protect the building's occupants.
|
|
|
Power for flux cored welding at high altitude: the SuitCase 12VS and Bobcat 250NT, plus (from right to left) Gary Wadsworth, Jim Truett, Pete Henrie, Harold (Red) Longacre and job foreman Brian Nordstrom.
|
In all moment connections, the horizontal beam flanges are full-penetration welded directly to the vertical column to provide bending resistance. The new provisions in the FEMA 350-353 welding codes (soon to be absorbed into AWS codes) are intended to ensure ductile performance. Beam webs are usually bolted to the column using shear connection plates. Columns are connected by a combination of full-penetration welds where they butt together (shown in Figure 2) and bolted together with sheer connection plates; the plates are then welded for added reinforcement.
X-ray Quality Welds
From March to October 2002, Intermountain Erectors welded and bolted in place 650 tons of A572 Grade 50 and A992 steel beams and columns. The structural integrity of the Four Seasons moment frames depends on the skill of Intermountain Erectors welding operators Gary Wadsworth, Harold "Red" Longacre and 18 other co-workers.
|
|
|
When complete, the Four Seasons Resort Jackson Hole will have nearly 1 million usable square feet and ski-in/ski-out access.
|
"To ensure subsurface integrity, all seismic welds are ultrasonically tested," says Henrie. "We haven't had a single weld fail a test in five years."
To put this quality achievement in perspective, consider that by the end of the Four Seasons project, Wadsworth and Longacre will have consumed 120 spools of wire. At 30 lb. for each spool and 2,500 in. per pound for .045-in. diameter E71T-11 wire or 2,750 in. per pound for .045-in. E71T-1 wire, that's more than 140 miles of wire used.
"The butt welds on columns of the residential moment frames take 12 passes to fill, but that's nothing compared to the 2-in. thick columns at the foundation of the main building," says Wadsworth. "Just a single connection requires 32 liner feet of weld for the cover pass alone. It takes me all day to weld one column. Me and my Miller welder have become pretty close friends."
|
|
|
A steel moment frame carries the sheer part of the building to give it more axial (side-to-side) and lateral (up and down) support.
|
Wadsworth's "friends" include the new SuitCase 12VS™ portable wire feeder and Roughneck® C-4012 gun, which are connected to the Bobcat™ 250 NT welding generator.
Equipment Selection
As noted, Henrie is pretty fussy about equipment. The type of flux cored wire used for structural welding requires a power source with a CV output (the Bobcat has a CC/CV output for Stick/TIG/MIG/flux cored welding). Other than that, equipment selection is Henrie's choice. Until last year, he specified the Bobcat 225 NT and paired it with a competitor's portable feeder. However, performance improvements in new Miller feeders and engine drives caused him to re-examine his choices.
First came the new Bobcat 250 NT. Henrie's older machines had a 16 or 18 HP gas engine and a rating of 200 amps at 20 volts, 100 percent duty cycle. While not always an issue at lower altitudes, Teton Village is 6,311 ft. above sea level. As a result, the output of the Bobcat 225 NT was marginal for running some .045-in. wires and the 5/32-in. E6022 "deck rods" used to weld the 18 gauge galvanized steel roof. Running 1/16-in. flux cored wire of any type was out of the question.
"We'd crank our old machines up to maximum and sometimes they still didn't have enough power because of lack of oxygen at high altitude," says Henrie. Fortunately, the scope of the Four Seasons project enabled Henrie to budget and order six new Bobcat 250 NT welding generators.
"I really didn't want to go with a larger diesel machine, so I was happy when I saw the new Bobcat 250 NT at a welding show in Colorado. With its 20 HP Kohler Command® OHV engine and stronger welding output, I knew it would have all the power we needed for flux cored welding and burning deck rods".
The Bobcat 250 NT has a CV output rating of 250 amps at 28 volts, 100 percent duty cycle. It produces 75 percent more total wire welding power than the Bobcat 225 NT (7,000 watts vs. 4,000 watts).
The Better Feeder
The next change came with the introduction of the SuitCase 12VS feeder to the Four Seasons job site. Operators were open to welding with this new feeder because it is 7 lb. lighter than their current feeder and eliminated several concerns related to feeding performance.
"Seven pounds may not seem like a whole lot, but it makes a big difference when I'm carrying the feeder up a ladder with a full roll of wire in it," says Longacre. "The other thing I like about the feeder is that its wire drive mechanism is just like a Millermatic® MIG welder. Anyone with shop experience can easily install a new spool of wire and adjust drive roll tension."
Henrie notes that wire feed performance on the competitive feeders has been an issue. "Welding wire has surface imperfections like small BBs on it. Sometimes those BBs come off, catch in the gun liner and stop the wire from feeding. Unfortunately, because our old feeders have one gear-driven roll pressing against an idler roll, the feeder didn't always grip the wire. The drive rolls would spin, prematurely wear the gear teeth and we'd have even worse performance."
To stop the wire from slipping, operators crank down on the drive roll tension (especially when a new set of drive rolls isn't handy). However, over-tensioning drive rolls crushes and deforms the flux cored wire. To demonstrate this problem, Henrie disconnected the gun from the feeder and blew air through it. The contact tip then emitted a cloud of smoke worthy of a cigar bar.
"That smoke is all metal shavings," he says. Shavings build up so fast that Wadsworth and Longacre had to blow out the gun liners on their old feeders several times a week. The liner wore out faster, too.
"Because the SuitCase 12VS uses two gear-driven drive rolls, it feeds the wire more positively," says Henrie. "The drive rolls and gun liner last longer, too. I've changed the liner twice on our old feeders, but I'm still using the original SuitCase 12VS liner after 35 or 40 boxes of wire."
Wadsworth agrees that, "The SuitCase 12VS definitely runs a little more smoothly than other feeders, and I like the feel of the gun in my hand. The ground wire is a lot more maintenance free, too."
Though still a skeleton in September 2002, the performance of Miller equipment and Intermountain Erectors will help complete the Four Seasons Resort Jackson Hole by late 2003. This 9-acre property will then have nearly 1 million usable square feet under its roof. In Wyoming, only government aircraft hangers in Cheyenne will be larger and, with its grand ballroom and penthouse hot tubs, nothing will be more opulent than the Four Seasons. The ski-in/ski-out access and spectacular view of the Teton Mountains helps, too.