While foundation pile work continues on the new $1.2- billion Gerald Desmond Bridge Replacement Project in Long Beach, CA, crews are preparing to build the structure's deck that will rise 205-ft-high over the bay. To safely work at such heights, they will employ two moveable scaffolding systems (MSS), which project officials say are a first in California.
"The MSS was selected because of its safety, quality and production advantages," says Bill Corn, project director with SFI JV, the entity in charge of the design-build project.
The MSS form systems are similar to standard cast-in-place forming, where the bridge is built span by span. But they have the "advantage of segmental construction where each span can be completed independently," says Corn. "The MSS concrete construction method is very similar to the traditional Caltrans bridge construction methods used throughout California. The local work force is already familiar with the methods of construction allowing the work productivity to be maintained."
The moveable MSS is a system that constructs a bridge one span at a time and is comprised of four primary elements: supporting brackets, main girders, transverse trusses, and exterior concrete forms.
The supporting brackets are attached to the columns and used to support the main girders. The support brackets also include the launching wagons to launch the main girders between the bents. The main girders are the primary structural element that supports the system between the columns.
The transverse trusses are connected to the main girder and used to support the soffit, or the “dance floor.” The dance floor is the starting point for the construction of the bridge superstructure and looks like a dance floor, says Corn. The final elements are the exterior concrete forms for the exterior slopping girder “sloper” and the overhang of the deck.
The MSS will be used to construct the approach structures between bents 1 to 15 on the west approach and between bents 18 to 28 on the east approach.
"The MSS was selected because it provides safe working access for labor equipment and material, while it does not obstruct access below the structure," says Corn. "Additionally, the quality is optimized with this kind of segmental construction because with span by span construction the construction process is similar to other bridges that are traditionally built in California, with the benefits of segmental construction."
The design-build project to replace the 50-yr-old Gerald Desmond Bridge began in 2013 and is scheduled to complete in mid-2018. Work is currently about 57 percent complete, with crews preparing to construct the east and west approach structures as well as the towers for the cable-stayed center span 205 ft above a shipping channel.
Duane Kenagy, P.E., Capital Programs senior executive lead, for the Port of Long Beach, says crews are also continuing the effort to construct the underground foundations consisting of 350 CIDH piles (cast-in-drilled-hole) with tip grouting, plus pile caps and columns.
"The two main 515-ft-high towers are under construction and should be completed in early 2017," says Kenagy. "Traditional falsework is under construction for the lower elevation approach structures, while the first of two movable scaffolding systems has been assembled and is set to place the first bridge segment."
The project is being led by the SFI JV of Oakland, CA-based Shimmick Construction Inc., Spain-based FCC Construction and Italy-based Impregilo S.p.A. Subcontractors include: Arup - lead designer; Irving, TX-based CMC Rebar and Gerdau Rebar of Santa Fe Springs, CA for rebar; Coolidge, AZ-based Stinger for structural steel fabrication and erecting steel; and A&A Concrete.