Finding Maximum Moment: Determining HL-93 Truck Position on Simple Spans

Abstract

In the days of the AASHTO standard bridge design specifications, engineers used simple equations for calculating the HS-20 live-load moment for a simple span bridge. Engineers computed and compared the lane load moments to the truck load moments. The larger moment controlled the design. The second axle of the design truck was not placed at midspan but rather at a 2 ft 4 in. (0.711 m) offset from midspan. The correct orientation of the offset required that the truck’s resultant force reside on the opposite side of the midspan from the second axle. As an example, for a 50 ft (15.240 m) span, this 2 ft 4 in. (0.711 m) offset yielded a