A METHOD TO PREDICT LOAD EQUIVALENCE FACTORS FOR SPECIALISED VEHICLES

Methods for predicting pavement damage caused by the passage of various wheel and axle configuration loads are examined. Factors considered are load, tyre size, tyre pressure, number of tyres, tyre spacing and axle spacing. Factors considered to influence pavement deflection under an axle are axle load, tyre size, number of tyres and tyre spacing. A simple procedure is developed for predicting the load equivalence factor, the ratio of damage caused by the specialised vehicle axle to that caused by a standard axle (where the standard axle is a load of 80 kn on a single axle with conventional dual tyres). The ratio for any axle is determined by the criterion that it causes the same damage when it produces the same maximum pavement deflection as the standard axle. Having determined the axle load which produces the same maximum pavement deflection as the standard axle, damage caused by some other load on the axle is then determined on the basis that damage is proportional to the fourth power of the load. Damage caused by an axle system is determined by summing the damage caused by individual axles. A step-by-step procedure for predicting the load equivalence factor for any specialised vehicle is presented (a). (TRRL)