A SIMPLIFIED METHOD FOR ESTIMATING THE NATURAL FREQUENCY OF BRIDGE SUPERSTRUCTURES

The draft edition of the limit state NAASRA bridge design specifications expresses the Dynamic Load Allowance as a function of the first flexural frequency of the bridge superstructure. In this paper, a simplified accurate method for estimating the fundamental frequency of bridges is proposed, and the higher vibration modes excited by vehicular traffic are examined. The significance of dynamic modulus of elasticity for concrete in vibration analysis is quantified. The effect of asphaltic concrete surfacing is also examined.