Chicago's skyline is one of the most impressive in the United States – skyscrapers and residential towers make a glittering backdrop to parkland and museum complexes reaching to the shores of Lake Michigan. Although it seems as if there could not be room for one more structure, a new condominium complex will soon be part of Chicago's skyline.
The Legacy at Millennium Park will feature 355 luxury condominium residences, along with parking and retail facilities. The 72-story tower contains one-, two-, three-, and four-bedroom units, and penthouses. One of the most striking features of the building is the glass-wall architecture providing floor-to-ceiling windows offering panoramic views of Millennium Park, Lake Michigan, Grant Park, and the skyline.
Given Chicago's harsh winter environment and the close proximity of other structures, including elevated train tracks, constructing The Legacy presented its own set of challenges. The contractor, Walsh Construction, wanted to create a closed working environment that would not only increase production, but would also ensure worker safety.
The contractor was especially interested in having a protection screen installed on the tower to protect workers from Chicago's windy conditions, and to help contain heat in the cold, wintery months. Since the Legacy's design is radial (curved) on one side, configuring and anchoring the protection screen posed another challenge. The protection screen would also have to be reconfigured as the building progressed higher and the perimeter got smaller.
Doka, a supplier of engineered formwork, was ready to meet this challenge by creating a customized solution for the contractor. Although Doka had successfully used protection screens on many worldwide building sites, this was the first application for its Xclimb 60 protection screen in the United States.
“Although The Legacy building is not a perfect geometric square – the building tapers as it gets higher – Doka was able to adapt the Xclimb 60 protection screen to the complex geometry of the building,” says Jim Milam, Doka field supervisor.
Doka preassembled the entire protection screen system in its factory and delivered it ready-to-use to the condominium work site. Made of trapezoidal sheeting, each protection shield unit consisted of two panels. Panels are placed on the wall and spliced to create one protection screen unit that is securely anchored to the structure. Doka was able to set 26 units to cover the entire perimeter, enclosing the top four floors at one time and safeguarding the slab-forming operations on the structure shell.
The room-high enclosure provided complete protection around the perimeter edges of the floor slabs where edge falsework and column-forming operations are performed.
“We found that the Xclimb 60 protection screen's modular panel system adapted very well to the building's unusual design,” says Milam. “The protection screen enclosed three floors at one time, protecting workers and preventing material from falling off the work area.”
Doka's Xclimb 60 protection screen is structure-guided at all times, even while being repositioned. Positioning shoes guide the screen's vertical profiles up the side of a structure, permitting safe, fast and efficient repositioning under any weather condition. Even in wind speeds up to 45 mph, an entire screen unit can be repositioned safety and easily in one lift.
Portable hydraulic components can be added to the Xclimb 60 protection screen to allow hydraulic repositioning, making it independent of a crane.
“The capacity of the windscreen and loading platforms to be moved without the crane allowed us to keep on task,” says Dan Regan, concrete manager for Walsh Construction. “We were surprised how quickly we were able to set the windscreen. Further, the windscreen provided a secure working environment for the slab-forming operations, which resulted in increased production of those operations.”
The contractor also requested a self-climbing loading platform, and Doka suggested using its Xclimb 60 formwork system. Designed for exceptional climbing safety, this system, when combined with the protection screen, provides full high-rise perimeter protection for the working floor and three floors below. The guided system connects to the wall with a self-locking mechanism, and provides for fast, safe repositioning of site material.
Four Xclimb 60 loading platforms were used at the Legacy site to transport materials from one level to the next. These loading platforms, which climb on the building's exterior, allow for easy cycling of slab formwork and safe climbing, even in bad weather.
“The Xclimb 60 loading platforms are lined up flush with the floor level, and material is rolled out directly onto the platforms,” explains Milam. “A crane picks up the material and moves it to the next level. All material is recycled, moving from the setting floor to the working floor.”
Walsh Construction was especially pleased with Doka's Xclimb 60 protection screen and loading platform system because it did not interrupt the three-day building cycle. With this cycle, one entire floor is completed every three days.
“Even with the geometric shapes changing on the building, Doka was able to modify its protection screen and loading platforms to keep up with the construction,” says Milam. “There was not interference with Walsh Construction's three-day cycle.”
Doka also took charge of providing safe transport of material from the ground up to the staging level on the 15th floor. Because the work site was so close to other buildings and the elevated train tracks, there was no room on the ground to position equipment or deliver material.
“We took extreme precautions to make sure that material was safely transported from the trucks on the ground level up to the staging area,” says Milam. “From level 15, we positioned the protection screens into their location without any problem.”
In 2009, when The Legacy is completed, Chicago will have a bright, new addition to its glittering skyline. Doka's customized, “out-of-the-box” solution gave the contractor just what it needed right at the job site. With Doka's equipment, production levels were increased and workers were safe, even on a building with a challenging design.
|Editor's Note: Anita LaFond is senior editorial manager for Constructive Communication Inc.|