Frost and snow could have disastrous effects upon modern pre-stressed concrete bridges because of the uneven expansion and contraction of the upper and lower surfaces.
LV. Towards Car coming towards on icy road, passes camera onto heated bridge.
LV. Towards Car travelling over bridge. Passes camera on to icy road, starts sliding more cars passing.
Bk. V. Car over bridge. Another car, coming towards camera pans.
Shot Snow falling on bridge and melting.
CU. Melted snow dripping through drain pipe under bridge.
SV. A technician examining the temperature below the bridge.
CU. Motor showing voltage.
SV. Technicians at voltage control.
GV. The Bridge.
LV. Pan From and covered rocks to man crossing bridge car pas???.
LV. Pan Car crossing bridge pan to snow covered rocks.
SV. Car having crossed bridge, skids on icy road.
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Background: Frost and snow could have disastrous effects upon modern pre-stressed concrete bridges because of the uneven expansion and contraction of the upper and lower surfaces. To combat this, Swiss engineers have fitted five such bridges at Murg, on the Walensee, with built-in heaters, comprising electrified wire mesh sunk into the concrete. The position of these bridges is ideal for the tests because they all lie within the shade during the three months of hard winter, so that variations which might be caused by the sun are eliminated. This particular bridge is kept at a temperature of 18 degrees fahrenheit above freezing point by passing only 25 volts through the insulated mesh. The tests, spread over the whole winter, will provide engineers with the statistics by which they will be able to decide the best temperature for all conditions and circumstances.