Bracing. Gary R. Steficek, SOM's project engineer for the commercial tower, adds that not all of the core bracing continues to the top of the building, either. Some of the bracing stops at the 16th floor, some stops at the 40th and the rest continues to the 50th floor. Tight bay spacing was needed at the corners to help transfer the wind loads around the corners of the building. There are four 11-ft-wide bays at each end and alternating 19-ft and 11-ft bays in the center. Each end bay has a chamfered corner. Columns that had beam stubs spiced on at midspan to form Ts were used between the 11-ft-wide bays. "The [horizontal] stubs were welded on in the shop where it is a lot easier to make a moment connection," says Steficek. Mosher Steel Co., Houston, fabricated the structural steel for the theaters and commercial tower. Steficek adds that the stubs could not exceed 5-ft because they had to be transported through tunnels into New York City. That meant that for the 19-ft-wide bays, stubs could only be shop-welded onto one side of the columns and additional beams for the frame had to be fieldwelded.
The steel framing that surrounds the tube in a wedding cake pattern at the building's base does not add to its stability. Steficek explains that the 18 floors of framing around the base of the tube carry only their own gravity load. The curved masonry on the exterior that is designed to mirror the arcade inside is six stories high. Steficek adds that the floor area varies from about 45,000 sq. ft at the base to about 25,000 sq. ft on the upper floors.
12. Answer the questions to part IV:
1. Who is the project engineer for the commercial tower?
2. Does all of the core bracing continue to the top of the building?
3. What was needed to transfer the wind loads around the corners of the building?
4. What columns were used between the 11-ft-wide bays?
5. What welding was used for the horizontal stubs?
6. What company fabricated the structural steel?
7. What needed field welding?
8. What is the steel framing compared to?
9. What load do the 18 floors of the framing carry?
10. How high is the curved masonry?
11. How does the floor area vary?