Measurement of Truck Load on Bridges in Detroit, Michigan, Area

Abstract

The objective of the study was to determine the actual truck loads on selected bridges in the Detroit, Michigan, area. Seven representative bridges were selected. The measurements were taken by using a weigh-in-motion system. For each measured truck, the record included vehicle speed, axle spacing, and axle loads. The variation in the accuracy of the gross vehicle weight (GVW) measurement was estimated to be ±5 percent and that of the axle weights was estimated to be ±20 percent for most types of trucks. Selected bridges were instrumented, and measurements were taken for 2 or 3 consecutive days. There was a considerable variation in traffic volumes and the weights of trucks, even within a given geographic area. The estimated average daily truck traffic varied from 500 to 1,500 in one direction. The maximum observed truck weights varied from 360 kN (81 kip) to 1100 kN (250 kip). The maximum observed axle weights varied from 90 kN (20 kip) to 225 kN (50 kip). The percentage of trucks exceeding the legal limits in Michigan varied depending on the road. The heaviest GVWs and axle weights were observed on Interstate highways. The largest percentage of overloaded trucks was observed for 11-axle vehicles. The maximum lane moments and shears from the trucks varied between 0.6 and 2.0 times AASHTO load and resistance factor design values. It was found that there are similarities in GVW and lane moment distributions.