Structural Engineering Award of Excellence: Tianjin CTF Finance Centre, Tianjin
Ronald Johnson
Associate Director
Skidmore, Owings & Merrill LLP, Chicago
Navigating the Elements by Working Outwards
The design and engineering approach to Tianjin CTF Finance Centre integrates three distinct program elements in a form that is both sculptural and rational. Working outward in a core-to-envelope approach, the sinuous topography is optimized to accommodate the relationships between different leasing spans, the varying structural core widths, and the perimeter walls. Square in plan with rounded corners, the structural approach integrates both architectural and engineering objectives.
The project is in an area of high seismicity, yet outriggers and dampers were not desired. Instead, a system of “soft braces,” consisting of variably sloped columns, optimizes structural performance for both frequent and rare seismic events. The sloping columns at the lower office zone do not engage each other at the center of the building, which allows for ductile deformation of the beams in the center bay, while the bays with sloping columns resist wind and frequent seismic forces. This allows the office floors to have relatively wide bay spacing while providing relatively high stiffness. A moment frame provides enhanced ductile performance through the middle zone. At the higher zone and crown, the sloping column system acts as a multistory belt truss. A belt truss at mid-height transfers the apartment-zone grid to the office grid, and transfers lateral loads to the megacolumns at the building’s corners.
Two additional levels of belt trusses equalize column shortening, and function as virtual outriggers to stiffen the building. Different column configurations were used over the height of the building, along with round concrete-filled-tube (CFT) columns in the office zone, to both minimize column size and reduce differential creep and shrinkage between the core and the perimeter.
