In seismic zones, construction of concrete high-rises keeps getting easier, thanks to advances in high-strength reinforcing steel used for confinement of high-strength concrete. The first use of 100-ksi rebar, in a just-opening 31-story tower in Seattle, is getting pretty high marks from the structural engineer and rebar fabricator. And the first use of a more price-competitive 90-ksi rebar in a project in nearby Bellevue, Wash., is getting even higher marks.
The advantage of using the material on both projects is reduced rebar congestion resulting from a reduction in horizontal rebar in columns and shear-wall boundary elements—by 40% for 100 ksi and 30% for 90 ksi, compared to standard 60-ksi steel. That means less field labor, less material that is lighter in weight, less hoisting, fewer problems threading things through the rebar and easier concrete casting. There also are fewer connections to 60-ksi rebar in beams and vertical rebar in columns and shear walls.
Because it can moderate the damaging effects of earthquakes, base-isolation is a technique used primarily in seismically active regions. ENR takes a look at some of the largest applications of base-isolation technologies in the world.