The 40-ft-long a-36 steel rails on a train track are laid with a small gap between them to allow for thermal expansion. determine the required gap d so that the rails just touch one another when the temperature is increased from t1=-20f to t2=90f. using this gap, what would be the axial force in the rails if the temperature rises to t3=110f? the cross-sectional area of each rail is 5.10 in2