Chicago is currently experiencing a boom in high-rise construction with 43 projects currently underway and more in the works. The tallest of this group is One Bennett Park near Navy Pier.
The new 69 story high rise building will include both rental apartments and condominiums. Standing approx. 255 m (836 ft) tall, One Bennett Park is the highest building in the Streeterville neighbourhood. The project also includes a large park that is actually the roof of a new subterranean parking structure.
The new tower is supported by belled caissons. The shafts of 18 of these caissons were reinforced by large steel cages made with 43 mm Ø, Grade 80 DYWIDAG reinforcing bars. In total, approx. 16,518 m of reinforcing bars including accessories was used for the reinforcement cages.
The original design consisted of cages with 36 mm Ø, Grade 75 reinforcing bars. This would have meant that 28, 85 and 105 reinforcing bars would have had to be installed into the cages. Due to the larger diameter of 43 mm bar, the number of bars was reduced to 19, 56 and 62. Going to the higher grade of steel and a larger bar diameter, 11 % of weight was removed and the total number of bars in the cages was reduced by 34 %, lowering the overall cost of material and labour and shortening the time to build each cage.
Another driving force in bringing down the cost of material was the ability to produce bars with customized lengths shipped direct from the mill to the jobsite.