Kolbjørn Saether

Kolbjørn Saether P.E., M.ASCE (July 16, 1925 in Trondheim, Norway – May 3, 2007 in Chicago, IL) was an American structural engineer in the City of Chicago for 47 years.

Saether dedicated his life to engineering and was known as a leader in his field.

He was a past director of the Structural Engineers Association of Illinois and was the organization's president from 1980 to 1981.

During his career he developed innovative engineering solutions for skyrise building construction that are now part of the Chicago skyline, published theoretical insights to enhance the state of the art in structural engineering, and patented novel techniques to advance the art of building construction.

400 East Ohio Street, Chicago, IL (1982)

400 East Ohio Street is a 50-story apartment building containing 85 flights of Saether Staircast stairs.

East Ohio was the first building to utilize Saether's invention of the Staircast System.

Office and apartment building, 30 East Huron Street, Chicago, IL (1983)

"A unique design resulting in a very slender structure in which the lightness of post-tensioned slabs were blended with an innovative method for reducing lower story moments through the use of outrigger supports."

Huron Plaza is 56-story high-rise with an adjacent 10-story garage located north of downtown Chicago.

The structural system is a post-tensioned cast-in-place concrete frame that forms the

exterior of the building with exposed architectural concrete columns and spandrel beams.

The typical floor is 70' X 130' yielding 9,100 square feet for a total of 510,000 square feet for the tower.

The garage is 80' X 180' or 14,400 square feet for a total of 144,000 square feet.

The design program asked for 8 office floors with a column-free area around a compact center core below 48 apartment floors.

Due to the narrow tower, it was necessary to provide three lines of "couple" shear walls to maintain acceptable stiffness.

The shear walls, however, could not be permitted within the 8 commercial floors at the lower level of the tower where only the shaft could be accommodated.

By modifying the "coupled-shear wall" design, it was possible to determine the effect of the "outriggers," resulting in a moment diagram for the shear wall, center core.

These moments were readily handled by the shear wall system.

The slabs were designed as a combination of oneway-banded design post-tensioned slabs.

The architectural layout did not lend itself to a straight and disciplined column layout.

This, however, was easily overcome by deflecting the banded-tendon runs in the traverse direction laterally to correspond to the column layout.

The longitudinal tendons were generally uniformly spaced except where they had to be deflected laterally around slab openings and mechanical obstructions.

Whereas the selection of post-tensioning was a natural choice for the 10-story parking garage, the decision to use post-tensioned design for the tower was based upon a number of circumstances.

The need for a column-free floor plan for the 8 commercial floors at the lower level of the tower, plus the need to place concrete shear walls on the dividing lines between the apartments, pushed the layout toward long-span designs with the typical spans in the order of 27'6". With weigh at a premium, only with post-tensioned design was it possible to achieve these spans with a 7" thick slab.

In order to allow casting of two floors each week, three days per floor, a slight upgrading of the concrete design strength was necessary, from fc'=4000 psi to 4600 psi.

On the other hand, with improved concrete strength, and relatively low shear stresses, it was possible to show that the post-tensioning greatly reduced the need for shoring and re-shoring, which allowed the finishing work to closely follow the casting of the concrete frame.

The more subtle advantage of post-tensioned construction is the resulting flatness of the slabs, making it easier for the finishing trades to install drywalls, shower bases, bathtubs and tiles, kitchen cabinets, and to align trims and moldings.

Also, the crack-free exterior spandrel system is to a great extent to be credited to the compression introduced by the pre-stressing tendons.

123 SW Jefferson Avenue, Peoria, IL (1984)

Twin Towers in Peoria, Illinois is a 28-story condominium and office complex, which used 120 flights of Saether Staircast stairs.

Twin Towers is truly a unique complex for Peoria.

Rising high above the city, the twin 28-story residential condominium towers afford owners luxurious living space and unexcelled convenience in a totally safe, secure environment.

3660 North Lake Shore Drive, Chicago, IL (1986)

The 48-story New York Private Residences is located in Chicago's Lakeview area.

The New York is the world's tallest masonry building.

Kolbjørn Saether generated numerous patents to provide cost saving solutions to various aspects of high-rise building construction.

A sample of some of his more influential innovations are listed below.

The Saether Staircast System is a uniquely designed system for erecting precast stairs in high-rise construction.

A launching truss consisting of individual, adjustable rigid steel frames interconnected to the precast stair flights, holds the stairs above the floor being constructed.