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Fast & frozen

By Nick Wright

Above: The USA Bobsled team’s BMW-engineered bobsled is competing in Sochi. Photo: USBSF

Athletes slide for gold atop miles of carefully welded steel pipe

February 2014 - When the Olympics come to any city, the ensuing flurry of construction transforms entire skylines, landscapes and even the dynamics of a community. Such is the case in Sochi, Russia, a subtropical vacation destination on the Black Sea. A city about the size of Honolulu, Sochi hosts the 2014 Winter Olympics and Winter Paralympics this month, and the before-and-after transformations of the city are impressive, with new stadiums, an Olympic village and new roads that have redrawn maps.

A 45-minute drive into the surrounding mountains reveals equally striking feats of engineering, fabrication and construction that are unseen in Sochi proper. Among those venues, such as the alpine skiing and biathlon courses (dubbed the “mountain cluster”), is the Sanki Sliding Center. The name seems to say it all. It’s upon this ice-covered concrete track that bobsleds (or bobsleighs), luges and skeletons slide down chutes and whip around banks in excess of 80 mph.

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At first glance, the Sanki Sliding Center resembles not much more than a giant concrete Hot Wheels track built into the side of a mountain, adorned with architectural metal and wood flourishes. The track has 17 banked turns, and is the only one in the world to have three negative slopes, where the athletes are sliding uphill. Also known as counter slopes, those sections have no turns, thus reducing speeds and increasing athlete safety. It takes 60 to 70 seconds to travel the entire track. At 1,814 m, it’s the longest track of its kind in the world.

Now, consider the ice that covers the track. In a subtropical region like Sochi, maintaining a frozen surface is a challenge. Embedded in the concrete are 100 km (62 mi.) of 1 in. seamless welded steel pipe that comprise the track’s refrigeration system—similar to the 2-D systems used beneath ice hockey rinks. The track’s refrigeration, sandwiched between a woven metal mesh and multi-layered latticework of rebar, gives the track not only its 3-D shape, but keeps the ice consistent. A warm spot in the ice here or there could be disastrous for the athletes careening along the track.

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Forming the track

Because there is only one Olympic sliding track constructed every four years, there aren’t many companies around the world that design them. It’s a niche area of expertise occupied by ISC/IBG Group, a Calgary, Alberta-based consortium of sliding track engineers from around the globe. The group is behind past sliding tracks in Vancouver (2010), Torino (2006) and Salt Lake City/Park City (2002). One interesting qualification of the group is that its employees are all connected with sliding sports in some way—either as former athletes, or they have family that compete.

Terry Gudzowksy, president of ISC/IBG Group, says the heart of the entire track is the steel pipe refrigeration system. “All of these tubes have to be bent and calculated based on the geometry of what the track has to look like,” he says. To that end, contractors and fabricators were constantly surveying and measuring the system as it was being installed. “We have to have everything in the right spot. You can’t have wiggle room here because of the geometry.”

The track’s refrigeration system is much like your own cardiovascular system. Similar to the heart, a pump house near the track circulates 150,000 lbs. of ammonia through the track in four sections. Because Sochi is at a lower latitude, it requires greater refrigeration capacity than a less tropical locale. This four-section system makes for more aggressive distribution to circulate more ammonia. It’s a 3.5-to-1 ratio overfeed of refrigerant per section. “A lot of people don’t realize if the sun breaks loose from the clouds and heats up a little spot, or if the wind blows a certain way, there can be slight irregularities. The overfeed system allows you to cover those types of unknowns,” says Dave Baranowski, a principal engineer at Salt Lake City-based Van Boerum & Frank Associates Inc., a member company of the ISC/IBG Group.

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The process for building any track begins with site selection. Gudzowsky says north-facing slopes are optimal to reduce sun exposure, although shading systems are incorporated. Contractors install adjustable I-beam supports and a concrete U-shaped foundation that contains the guts of the track: utilities and the refrigeration pipes. It serves not only a structural purpose—in the unlikely case of an ammonia leak, it’s contained in the foundation.

When the pipes are placed on the track, they’re spaced 90 mm apart, center-to-center, for uniform cooling. During welding, cleanliness is key. The fabricators kept caps on the open pipe ends during installation to prevent debris from getting inside, which could collect in the pump compressor and create jams. Once a section of refrigerant piping is complete, it’s topped with a diagonal lattice of 10 mm rebar. That shape helps the structure conform to the track’s curves. Removable plastic pipes placed perpendicular to the track serve as depth guides for the concrete. In this case, shotcrete, a concrete that is sprayed on, is applied at 15 cm thick for the walls and 35 cm thick for the track’s bottom.

Made in Russia

As with any Olympic construction site, the International Olympic Committee and the international sport federations give their requirements to an organizing committee, which in turn sources local fabricators and construction outfits. The organizing committee selected Moscow-based Olympstroy, which formed in 2007 to oversee construction of all the Sochi Olympic venues, including the roads, rail and infrastructure upgrades.

For the Sanki Sliding Center, Olypmstroy hired Mostovik, a Russian fabricator and construction company, as well as metal supplier. Mostovik worked alongside Rusenergomontazh, a contractor based in St. Petersburg, which welded the pipes for the vapor compression refrigeration system, according to ISC/IBG.

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 Baranowski says the pipes are 1 in. A53 grade B, schedule 40 steel, which was supplied pickled. The Sochi track uses seamless pipe, but that spec was the contractor’s preference. Salt Lake City’s track, for example, used ERW pipe. “Out of 330,000 ft. of pipe we had one leak in Salt Lake City, crazy as it is. Sochi is seamless, that’s their choice,” he says. The construction is built to Russian and German standards, which generally follow highly-regarded North American and European standards for construction and fabrication. Similarly, the Russians weld to their Gosstandart, or GOST standard, analogous to welding codes in U.S.

“They generally model the American Welding Society, so there’s continuity in the process which means you can get equivalent products worldwide. It’s very encouraging,” Baranowski adds.

The pipes were set into place on jigs, whereupon the pipes were surveyed and adjusted as necessary. A total of 800 templates and gauges were installed, and surveyors monitored every welding seam, according to Olympstroy. The fabrication team at Sochi conducted a 100 percent radiographic exam of all welds done in the shop; in the field, it was 25 percent, “which is pretty extreme,” Baranowski says. Next, the pipes were subjected to a 200 psi nitrogen test during the shotcrete process to find any leaks. “If we lose pressure on our gauges, we’ll have a leak to repair, and that’s done on the spot,” he says. In all, 10,000 precision welding seams were required to complete pipeline joints, according to Olympstroy.

Before the 1,050 m3 of shotcrete making up the track buried the pipes and rebar, the raw steel appeared as a complex metal fretwork. In reality, it was a practice in engineering perfection. The entire three-dimensional structure was built within 1 mm tolerance. Plus, the pipes were formed with a CNC tube bender off-site before being installed. Data from CAD drawings were uploaded to the bender, ensuring nothing was out of spec. Any slight deviation could have thrown off the track’s geometry.

Icing on the track

To the tune of $50 billion, the scale of construction makes Sochi one of the most expensive Olympics on record, placing it under heavy media scrutiny. The Sanki Sliding Center, one of the projects completed on time and without major hang-ups, was built in just 22 months, beginning in April 2010. The track’s homologation, or commissioning, was completed in February 2012. About a year later, the International Luge Federation hosted its World Cup competition on the track, giving the world the nod that the track was ready for the games.

The culmination of years of engineering, design and meticulous fabrication is all focused on the quality, constitution and consistency of one key variable: ice. 

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According to Viktor Pryadein, vice president of Olympstroy, making ideal ice is an extremely slow and painstaking process. “Our track is 1,814 m long, and specialists must work on every meter and centimeter of the track. After the ice is accumulated, it must be polished to such an extent as to eliminate all rough surfaces. This is needed to reduce friction and, of course, to ensure safety,” he said in a statement.

For several reasons, there is no uniform thickness of ice on any sliding surface, Gudzowsky explains. In general, the ice crews aim for a layer about 2 cm to 4 cm thick. Ice makers also aim to make the ice as thin as possible so that the ice surface replicates the contour of the track.

“For example, on a straightaway, the amount of pressure exerted on the ice by the sleds is very low so a thinner layer of ice can exist without risk of it breaking down. In a corner, the sleds exert higher pressure on the ice; therefore, that ice has to be thick enough to maintain its integrity,” he says. 

Weather is also a factor. The Sanki Sliding Center passes through several microclimates, where some portions could be sunny or shady. The track’s top and bottom are at 836 m and 704 m above sea level, respectively. The concave track, which is designed for luge, bobsleigh and skeleton events, has five starting positions at different altitudes and distances from the finish line.

“If it is relatively warm, then the ice makers may want to increase the thickness of the ice to some degree to maintain its integrity in case of melting,” Gudzowsky says. “Also, while sleds are making descents, the ice makers will often spritz the track with a water hose in vulnerable areas to make sure that the ice does not break down.”

The Sochi track is designed for use at a maximum air temperature of 22 C (72 F), made possible by refrigerant pumping through at minus 12 C. Temperature sensors in the track give crews important real-time data because the net altitude of the track drops 125 m (400 ft.). Crews can react accordingly, and rest assured the refrigerant will flow where it’s needed. FFJ

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