Dorton Arena - Pushing the Limits: New Adventures in Engineering - page 85

Dorton Arena
Not very long ago, I picked up at the Raleigh-Durham airport a prominent and very busy structural
engineer who had flown in from Chicago to give a talk at Duke University. As we were driving
toward Durham, I asked him if there were any structures in the area that he would like to see during
his brief visit. He did not hesitate before naming just one: Dorton Arena. Since we were driving in
the opposite direction from Raleigh and the North Carolina State Fairgrounds on which the arena
sits, and since we did not have that much time to spare before his talk, I told him we would risk
getting caught in traffic if we went there first. Perhaps we could go by after his talk.
Dorton Arena, completed in 1952, was an early stadium-like structure designed to enclose a large,
covered, column-free space. It is thus a predecessor of such covered stadiums as the Houston Astro-
dome, completed in 1965, and the variety of superdomes that so dominate sports-stadium design
today. Yet for all of its influence on subsequent design and construction, the significance of the
unique Dorton Arena remains relatively unknown outside the structural-engineering and architec-
tural communities. Instead of relying strictly on the primitive principle of compression, in which
loads are carried by bearing down on what supports them, as do pyramidal piles, planar walls, cir-
cular arches, and domes of stone, the Dorton Arena is a structure with a roof that is supported in
tension.
Tension structures carry their loads by resisting being pulled apart. Suspension bridges, with their
graceful cables, are very prominent tension structures. Tents are also tension structures, with their
fabric stretched over poles the way the bridge cables are slung over towers. Indeed, although not of-
ten visualized in this way, a large circus or event tent can appear in profile or silhouette to resemble
a suspension bridge or a number of suspension bridges in tandem. Because tensile structures work
by resisting being pulled apart, they also have to pull against something; thus, suspension bridges
require anchorages, as tents require stakes in the ground, to maintain their configuration. Among
the Dorton Arena's unique features is the elimination of any anchorage or stakelike components,
making it a more economical and elegant structure. So how does it bear the essential tension?
The roof cables pull against a pair of crossed and inclined concrete parabolic arches that are per-
haps the arena's most dominant feature. Like all arches, these work in compression, and the pull
of the cables in the plane of each arch is transformed into a compressive force that flows down the
legs of the arch into the ground. The structural action of the building has been given the anthro-
pomorphic interpretation of being like two men who lock arms and pull against each other. If they
were standing upright, their mutual pulling action would tend to make them fall toward each other.
To keep this from happening, each of the men can place his feet behind those of the other as he
leans backward and pulls with his arms. In this cross-tied stance, each would only fall backward if
he let go of the other. However, the men might also slide on the ground if they did not have their
heels dug in or their legs tied together in some way. An analogous action is going on beneath the
surface in the Dorton Arena, where the feet of the arches bear against massive abutments and where
the crossed legs are tied together with steel cables.