ANALYSIS OF DYNAMIC BEHAVIOR OF ROADS SUBJECT TO LONGITUDINALLY MOVING LOADS

THE FLEXURAL MOTION OF A LONG ROAD PAVEMENT OF UNIT WIDTH, VISCOUSLY DAMPED AND UNIFORMLY SUPPORTED BY AN ELASTIC SUBGRADE, WAS FOUND FOR THE CASE OF A STEADY, NORMAL, CONCENTRATED LOAD MOVING LONGITUDINALLY AT CONSTANT VELOCITY. DEFLECTIONS OF THE PAVEMENT WERE WRITTEN IN TERMS OF THE ROOTS OF THE CHARACTERISTIC EQUATION ASSOCIATED WITH THE EQUATION OF MOTION OF THE PAVEMENT. A DETAILED STUDY OF THE ROOTS DEMONSTRATED THAT THE SOLUTIONS FOR THE DEFLECTIONS FALL INTO THREE DISTINCT REGIMES DISTINGUISHED BY THE VALUE OF THE DISCRIMINANT OF THE FOURTH-ORDER CHARACTERISTIC EQUATION. IN TERMS OF THE CONCEPTS OF /A/ SUBGRADE DAMPING RATIO, /RATIO OF SUBGRADE DAMPING COEFFICIENT TO SUBGRADE CRITICAL DAMPING/ AND /B/ THE VELOCITY RATIO, /RATIO OF THE LOAD VELOCITY TO THE PROPAGATION VELOCITY OF A TRANSVERSE-DISPLACEMENT WAVE ALONG A FREELY VIBRATING, ELASTICALLY SUPPORTED PLATE OF UNIT WIDTH WITH ZERO DAMPING/, IT WAS FOUND THAT FOR LIGHT DAMPING IN THE SUBGRADE /SDR LESS THAN 0.7/ AN INCREASE IN THE VELOCITY OF THE LOAD TO THE VICINITY OF A VELOCITY RATIO OF UNITY PRODUCES AN INCREASE IN THE DYNAMIC VALUE OF THE MAXIMUM PAVEMENT DEFLECTION. FOR HEAVY DAMPING IN THE SUBGRADE /SDR GREATER, OR LESS THAN 0.7/ AND INCREASING LOAD VELOCITY, THE MAXIMUM DEFLECTION DECREASES FROM THE CORRESPONDING STATIC VALUE. THE LATTER RESULT IS OBSERVED TO BE IN ACCORDANCE WITH MEASUREMENTS THAT HAVE BEEN OBTAINED BY OTHERS. /AUTHOR/