The new City Hall Annex in Roseville, Calif., is the first precast concrete building ever built in this rapidly growing city, and the first to be accredited by the U.S. Resiliency Council (USRC) for its seismic capacity.
But its strength is not the only attribute that make this structure special. As the most prominent building downtown, the owners wanted a structure that would convey a sense of stability and stature appropriate for an important civic building, without overshadowing the City Hall next door. It was also important to demonstrate responsible use of public funds.
Like many award-winning projects this year, design of the annex did not initially include precast concrete. However, during schematic design, the project team determined that switching from steel to a precast concrete structure would result in multiple benefits for the city. “Precast concrete was a building material that provided durability, structural reliability, sustainability, and provided the presence of a stable and permanent civic structure,” says Curtis Owyang, vice president and principal at LPAS Architecture + Design in Sacramento, Calif.
During the design phase, the precast concrete producer presented value-engineering ideas that removed columns and used double tees to create 56-ft spans, with hollow-core slab for the remaining 28-ft span. That concept reduced costs and helped get precast concrete within the cost range of the steel system, while lowering long-term maintenance costs. The panels used integral colored concrete with three different levels of sandblast to mimic the architecture of City Hall, says Farid Ibrahim, director of preconstruction services at Clark Pacific in West Sacramento, Calif. “The recessed windows set in the precast exterior also recall the pattern, proportions, and detailing of City Hall.” The use of precast concrete also helped meet the tight 12-month deadline.
One of the most unique attributes of this project was the use of a precast hybrid moment frame for seismic resistance. This system uses precast concrete column and beam elements connected with reinforcing bars and post-tensioning to absorb energy caused by movement of the joint while simultaneously holding the joint together during an earthquake. “It has the unique ability to self-right after a major seismic event,” Ibrahim says. Internally, the use of the precast hybrid moment frame system also allowed for the elimination of two lines of columns, opening up the space and providing more flexibility for planning.
No less than 538 precast pieces, including panels, columns, beams, walls, double tees, and hollow-core slabs, were manufactured off-site in just 10 weeks. Casting the pieces off-site helped ease congestion and allowed for “just-in-time” delivery of pieces to the jobsite. The carefully scheduled delivery process kept the project on track, and the entire structure was erected in just 38 days. “Precast construction was efficient from a material use standpoint as well,” Ibrahim says. “By fabricating the building parts in a controlled facility, a higher degree of precision can be attained while minimizing wasted material and time.”
The result is an efficient, functional, resilient, and cost-effective building that effortlessly fits into the fabric of the community. Referring to the project, Mike Isom, development services manager at City of Roseville, says: “We have an obligation to our local taxpayers that we’re being as efficient as possible with the resources we have available. Clark Pacific has gone a long way in helping us to do that.”