I've seen a few calibration courses set up on bridges, and have a question:
Since bridges expand and contract with temperature variations (notice the expansion joints at either end) is the calibration considered valid only at the temperature at which it was originally taped off? Or is the expansion not enough to worry about?
This is merely to satisfy my own curiosity.
I suppose the same discussion holds true for cal courses on regular roads as well.
Good question. The coefficient of expansion for steel is 3.3 (m/m.K x 10-6). Consider temperature extremes of 0 deg C to 40 deg C. This will be a change of 0.02%. Much smaller than our SCPF of 0.1%. If the two ends of the course are on solid ground on either side of the bridge, there should be no effect. A road should not be affected since it is attached to the ground.
I wondered about this in 1985 when participating in a group ride to measure the New York City Marathon. When we rode across the Verrazzano Narrows Bridge, we had to dismount in at least two places and carefully wheel across giant expansion joints. These joints were like the fingers on two hands pushed together so that they were adjacent, but permitted some back-and-forth movement. As I recall the range of relative movement was five or six feet. The gaps between adjacent fingers were barely wider than a narrow bike tire, and only a circus rider could go across non-stop without experiencing pain. Autos, with nice fat tires, of course have no problem.
As Alan has pointed out, the bridge deck is not going to expand and contract that much, but it is curved, and supported by the suspension structure, which expands and contracts also. Cold weather will raise the deck, making the bridge a bit longer, while warmer weather will lower it, shortening the bridge.
I lack the capability to calculate how much actual movement occurs in those monster expansion joints, but I’d bet it’s a foot or more.
Perhaps we need an RRTC rule to prohibit calibration courses from crossing suspension bridge expansion joints.
While we're on the subject of"different" cal courses, what about a course that has been laid out on a street that later had speed bumps ( or speed humps for that matter) added.
Is it still valid?
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