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A bridge to be fabricated of steel girders is designed to be 500 m long and 12 m wide at ambient temperature (assumed 20C). Expansion joints will be provided to compensate for the change in length in the girders as the temperature varies. Each expansion joint can compensate for a maximum of 20 mm of change in length. From historical records it is estimated that the minimum and maximum temperatures in the region will be -35C and 40C, respectively. Determine (a) the minimum number of expansion joints required and (b) the length that each bridge section should be fabricated. The coefficient of thermal expansion a=12(10-6)/C for steel. Aluminum has a density of 2.70 g/cm at room temperature (20C). Determine its density at 500C.