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A palace of parts
By Kevin Flynn, News Staff Writer Think of the juicy sections of a tasty, plump grapefruit halved on your breakfast plate, and there you have an analogy for Invesco Field at Mile High. Because of its size and shape, the building that is the Denver Broncos' new home turf was built in eight distinct segments so that the mammoth superstructure and the steel-and-concrete filling can expand and contract in the severe Colorado weather extremes. From 30 below to 105 above, and even from the height of a summer afternoon to the mild nighttime cool-down, the stadium will be moving as much as six inches per section. A $400.2 million project that opened six days shy of just two years from its groundbreaking, Invesco Field's construction was phased so that each of those segments could be tracked separately from one another. Progress on each was charted as a separate item. While structurally distinct, the segments are inescapably linked together by utility systems such as electrical, plumbing, heating, communications and security, such as fire alarms. Charlie Thornton, project manager for the Turner-HNTB joint venture that led the construction effort, said provisions are made at the building joints to keep those systems secure as the building expands and contracts. It is essential in construction to provide for expansion of materials in heat and contraction in cool weather by building expansion joints. Frequently these will appear in larger buildings as metal plates across the floors and up the walls, and hidden above drop ceilings, bridging the open space of several inches between building segments. For Invesco Field, designers segmented the structure into eight pieces -- spaced roughly like the straight edges of a stop sign at north-south-east-west and at the four diagonals. "As a closed ring, if it were built in one piece, as temperatures changed with all the materials in it, the building would start to rip and tear," Thornton said. Even during construction, the steel treads and risers that form the floor for the seating bowl could be heard creaking under the heat of the summer sun and popping in the cool of the night. That's the noise the building is supposed to make. Thornton said the segmenting also helped construction meet the legal demands of the project. Erecting segments independently allowed the stadium district to keep McNichols Sports Arena open until the Pepsi Center, which replaced it, was ready. McNichols was soon demolished so that the southwest corner of Invesco Field could go up. Also, Denver's timetable for conveying land ownership to the stadium district -- Invesco Field was built on four separate legal real estate parcels -- didn't delay construction because workers could concentrate on segments located on district-owned land while the city waited to convey the remainder. At Mile High Stadium next door, built with additions over a 38-year period, material expansion problems were handled with each new segment. From the original west and north concrete lower level to the independently standing skyboxes that loom over the west grandstands, it is effectively in segments also. The entire east stands structure, from field level to the lights high atop, moves as a unit back and forth since it was originally designed to accommodate the larger baseball field as well. Contact Kevin Flynn at (303) 892-5247 or flynnk@RockyMountainNews.com.
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