Author: Dr. Alireza Akhtari
1- SOCIAL, POLITICAL and ECONOMIC CONTEXT:
In the late-1970’s, there were several components that lead to the recovery of the building market. First was a rise in the number of office workers and a corresponding demand for office space. The second component was the staunch support of the new presidential administration of Jimmy Carter to revitalize and restore urban areas through urban-aid programs and federal grants. With this commitment, President Carter wanted to promote the idea that urban areas are “the backbone of the social and economic structure of our country.1” This led to a rise in government funded projects specifically for metropolitan development.
At the same time, Fazlur Khan’s mentorship with graduate students at Illinois Institute of Technology facilitated the ongoing research of evaluating the effectiveness of different structural systems. Based on the work of one of his students Robin Hodgkison, Khan decided to implement the idea of a diagonally braced concrete building for the Onterie Center.
Location: Chicago, 441 East Erie St
Start of Construction: 1979
Number of Floors: 58
STRUCTURAL SIGNIFICANCE :
Regarded as Fazlur Khan’s last major project, the Onterie Center is a mixed-use development with residential, office, and retail space. Currently the 57th tallest building in Chicago, this concrete trussed tube structure is visibly accentuated by its concrete in-fill panels. The Onterie was the first concrete high-rise in the world to use diagonal shear panels at the perimeter.
STRUCTURAL SIGNIFICANCE :
The Onterie is comprised of two buildings, a 58-story main tower and a 12-story auxiliary tower. Figure 2 shows a street view of the building. The combination of closely spaced perimeter columns and spandrels as well as the integration of diagonal concrete infill panels make up the lateral load-resisting system. As a whole, these infill panels create X-formations on the perimeter serving two purposes. The first is to act as shear panels to resist the effects of lateral loading, and the second is to join the perimeter columns and spandrels to distribute vertical loads. Figure 3 shows an infill panel detail where the reinforcement ties the vertical and horizontal systems together.
Figure 4. illustrates one challenge with designing this type of structural system. As its shown in the figure below, the horizontal component of the axial force in the diagonals induces a force at each corner where the braces meet. Typically these forces are resisted with the presence of a perimeter tension tie that essentially bounds the structure in place. However, in the case of the Onterie Center, this horizontal thrust is resisted by increasing the depth of the slab and adding additional reinforcement in the spandrels.
The base of the tower spreads to create more office space and to increase the amount of sunlight that enters. The main public lobby for the main and auxiliary tower contains retail space. Floors 6-10 of the main tower and floors 2-11 on the auxiliary tower are for office space. The additional floors are residential spaces.
Special thanks to: Farideh Givehchi