Building From the Outside In
Building From the Outside InSkyline at MacArthur Place gets a boost from Outside Tie-In and Pin Tower technologies
STURTEVANT, WI (July 30, 2007) – The scarcity and cost of land in Orange County, California, (the O.C.) has thrust developers into building high-rise towers as homes for retirees, young professionals and families, instead of the traditional single-family homes. With the rapidly increasing growth of high rises as living quarters in the O.C., Skyline at MacArthur Place is one of the more than 50 high-rise development plans in progress, which means southern California may resemble a Miami-like skyline in the very near future.
Population Growth Prompts Vertical Living
“There are about 40,000 home lots left in Orange County,” says Cory Alder, president of The Nexus Companies, the developer and general contractor for the Skyline at MacArthur Place project. “Phoenix, Arizona, where they had 70,000 housing permits in 2005, has the same population as the O.C. This basically means the area will be out of land very soon.”
According to Alder, the scarce land and rising living costs are not the only triggers for the vertical living evolution hitting the O.C. The trends of baby boomers who have become empty nesters looking for a lower-maintenance home, and young business professionals who want to be “near it all,” have also played a role.
“Skyline will be the most upscale urban alternative for those seeking a contemporary lifestyle free of long commutes and home maintenance,” says Alder. “Skyline is close to South Coast Metro’s best shops, restaurants, arts and entertainment venues. We expect Skyline to redefine urban living and help transform South Coast Metro into a 24-hour community, a place where people can truly live, work and play.”
The two 25-story towers broke ground in June 2006 and are slated for completion in 2008.
Outside vs. Inside
When Nexus and Largo Concrete, Inc., the concrete contractor for Skyline, met to discuss the different concrete placing options they had for this development, the timeline of the project was key, according to Ted Rebelowski, project executive for Largo.
“The timeline of the project is what mainly drove the decision for Nexus to use an outside tie-in placing system versus an inside placing system,” notes Rebelowski. “Both Putzmeister’s outside tie-in and inside placing systems are reliable and efficient; however there was no ideal location for us to install an inside placing system in the Skyline towers. The elevator shafts, which are commonly used to hold inside placing systems, needed to be in use as soon as possible, so those were ruled out for the inside placing system location.”
According to Rebelowski and Fred DeFalco, senior superintendent for Nexus, using an inside placing system that is not in an elevator shaft would mean going back into the building to fill the area supporting the system with concrete after it is removed and most of the concrete is placed. This could result in project delays.
“The finish trades of the project, such as the dry wall, painters and electrical, would be delayed using the inside placing system option,” says DeFalco. “We were thrilled to learn from Largo that there was an outside placing option for us.”
“Putzmeister’s universal tie frame enables us to secure the tower outside the structure, therefore minimizing disruption to other trades inside the building,” notes Rebelowski.
“The only location where the outside tie-in impacts the building is where the system ties into the floor. The glass section on the floors where the system is tied in has to be left out until the freestanding tower rises to its next floor,” comments DeFalco.
To learn more about other placing boom tower mounting options, you can read the article, “High Rise at High Speed” to see what the inside climbing system can accomplish. This article is available in the news section of the Putzmeister America website at: www.putzmeister.com.
A First on the West Coast
Rebelowski and his team at Largo called on Dan Navarro and his crew at the Oak View-based JLS Concrete Pumping in fall 2006 to provide their 36/40Z-meter placing boom, two of their state of the art Putzmeister outside tie-in systems and freestanding Pin Towers, as well as their 28Z-meter truck-mounted boom pump that has a .16H pump cell. JLS’s 28Z-meter has also placed about 35,000 cubic yards of the total 55,000 cubic yards needed for the Skyline towers, according to Navarro.
“This is the first time on the West Coast that a Putzmeister pin tower is being used on an outside tie-in project,” says Navarro. “It’s great to see contractors taking advantage of this innovative technology. When I provide the contractors with different placing system options, most now choose outside tie-in.”
According to Navarro, about 75 percent of his projects use outside tie-in. “The placing boom industry is being revolutionized for the 21st century with this modern technology often seen in use with tower cranes.”
The freestanding pin tower is mounted with foundation anchors. According to Navarro, the outside tie-in and pin tower combination allowed JLS and Largo to overcome an extreme challenge in placing the concrete.
“We have to tie the universal tie frame three different times, on both the North and South Towers,” notes Navarro. “Currently the tie frame is in its first position at eight feet away from the building on the seventh floor. The next position is at the 12th floor on both towers where the tie frame will stay eight feet away from the building. Floors 18 and above step back 18 feet to the face of the lattice tower.”
As an added bonus for JLS, the heavy-duty pins on the pin tower allow for a faster and easier connection in installing and raising the freestanding tower on both the North and South Towers.
“Because the pin tower doesn’t require bolts, we don’t have to worry about needing special tools or torquing bolts,” notes Navarro. “ This saves time and money.”
Of the Putzmeister placing system technology, DeFalco says, “Their equipment is nothing short of great. We’ve used it before and have always had success with it.” He also adds, “JLS is a pleasure to work with, they’re always on time and are very knowledgeable about the placing system technology.”
Considering the Mix
There are two main concrete mixes being used on the project, according to Rebelowski and Al Campos, field superintendent for Largo.
“A 5,000-psi concrete mix is being used for the decks. The freestanding tower is anchored down securely which means the 36/40Z-meter placing boom is able to place the concrete mix at the pace of 100 cubic yards per hour without the placing boom’s end hose searching, or moving, as much as if it weren’t secured as firmly as it is,” comments Campos.
For the core walls, columns and downturn beams, according to both Rebelowski and Campos, a rich or “hot” 8,000-psi concrete mix was used.
“This was a challenging mix to specify because southern California has naturally poor aggregate. As a result of the poor aggregate, we have to add more cement content than usual to the mix,” says Rebelowski. “In other locations, such as northern California, they don’t have to use as much cement as we do. If we have to use 10 sacks of cement per yard to achieve an 8,000-psi concrete mix, then northern California would probably use about six sacks per yard to achieve the same amount of psi.”
“Additionally, this hot mix was tricky to place,” says Campos. “With the large amount of cement in the mix, we needed to work closely with JLS to specify a mix that would be pumpable. If the concrete becomes sluggish in the delivery line, the pipe could freeze and we couldn’t take that risk. We needed to make sure the mix specified would keep flowing, to prevent it from hardening. At the end of each pour, we blow the delivery line back with air using a foam ball. This prevents the concrete from setting up in the delivery line.”
Placing the Concrete
To place the 50,000 cubic yards of concrete to the top of the 300-foot high North and South Towers for Skyline, JLS has their 28Z-meter boom pump at ground level. Concrete is pumped from the boom pump’s SBU hydraulic circuit on the head side where a slick line travels to the freestanding pin tower and up to the placing boom on either the North or South Tower, according to Navarro.
JLS opted to use their truck-mounted boom pump versus a trailer pump because of its versatility, says Navarro. “When we were done with deck pours in the lower levels, we could use that same boom pump that same afternoon to place concrete for the walls and columns. All we had to do was hook the back end of the pump up and adjust the release valve to go through the boom, and we were ready to roll.”
According to Navarro, the truck-mounted boom pump was then able to reach up to 1,800-psi concrete piston head pressure and up to 140 cubic yards per hour.
In late June 2007, JLS placed 450 cubic yards of concrete for the seventh floor of the North Tower.
According to Rebelowski, about 400 cubic yards of concrete on a 16,000 square-foot deck are placed with the boom on the Skyline project every four days for both of the towers.
“After a deck is placed, the next day we immediately place about 200 cubic yards of concrete for the walls and columns,” notes Rebelowski.
According to Rebelowski and Navarro, this tight schedule keeps the project moving along and will continue until they reach the top of both towers.
JLS will be on the site until the placing of the concrete for the two towers is complete in January 2008.
Looking into the Future
When complete, the North and South Towers will offer residents numerous luxurious features:
•349 ultra chic, spacious condominium homes including luxury penthouses on the top levels.
•Homes boasting extraordinary views of the Orange County skyline.
•Spacious one to two bedroom floor plans ranging from 1,018 to 2,800 square feet and priced from $700,000 to $2.8 million.
•A two-and-a-half acre lake surrounded by scenic walking path.
•Resort-style, half-acre outdoor amenity deck including a junior Olympic swimming pool, two Jacuzzi spas, barbeque and picnic areas with fire pits, bocce ball court and putting green.
•Spa clubs with sauna and steam rooms, massage rooms and relaxation areas.
•3,700-square foot fitness center with state-of-the-art equipment and yoga/pilates studio.
•The 3,000-square foot entertainment lounge offers a full demonstration kitchen, pool tables, game tables and a wine bar.
Although completion of the North and South Towers for Skyline will be in 2008, Nexus still has their work cut out for them. There is a third tower that will be built as part of the Skyline complex. The tower will be 25 stories high, similar to the North and South Towers, and will include 150 condominium units. This section of the project will be called “Skyline Phase II.”