Getting fresh concrete to flow freely around an intricate maze of rebar has always been a challenge at construction sites throughout the world. Hanns Baumann found this out for himself several years ago in San Francisco.
He was having difficulty getting the concrete around rebar on a 17-story dormitory building at San Francisco State University. After some brainstorming, Baumann, who was serving as a consulting structural engineer on the project, came up with BauGrid Welded Reinforcement Grids (WRG). Baumann's system does not have many of the hoops, stirrups, and crossties found in conventional reinforcement cages in columns, beams, and sheer walls. This saves material and labor costs, leading to lower overall construction costs.
Today, Baumann, a consulting structural engineer for 50 years, leads BauTech and BauGrid Construction Systems of Laguna Beach, Calif. Specializing in reinforced concrete construction, he has received seven U.S. patents and is a co-inventor on two others.
BauGrid's WRG is manufactured from cold-drawn, high-strength steel conforming to ASTM A82. Delta Building Systems has an exclusive license from BauGrid to manufacture and distribute the product in North America and Asia. “We sell the product directly to precast producers who make their own rebar cages, in addition to rebar companies who deliver cages to the project site if it's poured in place,” Baumann says.
Baumann says his unique reinforcement system has several advantages over conventional reinforcement. “We use high-strength steel, so it is lighter,” he says. This leads to a 50 percent savings in confinement steel weight, resulting in savings in labor in assembling and installing the cages. Also, the “corkscrewing” of cages at the jobsite is nearly eliminated, which reduces crane time. Other advantages include minimum wire tying and savings in construction time. With plus or minus 1/8-inch manufacturing tolerance, it is possible to install a two-story cage with vertical rebar couplers in 30 minutes.
The company also claims the product leads to improved ductility, which results in better seismic performance. The Precast Seismic Structural Systems (PRESS) research project, partially funded by the National Science Foundation and the Precast/Prestressed Concrete Institute (PCI) concluded that conventional reinforcement was not as economical as the BauGrid system, Baumann says.
The system has been used in projects in many California cities, including San Francisco, Los Angeles, San Diego, Long Beach, Oakland, and Daly City. Five-eighth-inch WRG was used in the shearwall boundary elements of the 40-story St. Regis Museum Tower, a condominium and cultural center development in San Francisco.
Also, the recently completed 60-story Millennium Tower in San Francisco, the tallest reinforced concrete structure in California, set several milestones for BauGrid application, including use of the product with high-strength concrete. So far, this is the tallest structure containing BauGrid in a severe seismic region.
“We used 2000 tons of the product and it was a huge success,” says Baumann. “There is no limits to the height of a building that can use this.”
For more information and to see a video, visit www.bautech.com.