Vertical Stress in the Gravel Decking of Log Bridges

As the forest industry moves into second growth stands with smaller tree diameters the design of gravel-decked log stringer bridges becomes more critical. This article considers the stress field at the base of the gravel decking. The results of this article indicate that stress equations derived from elastic theory for a semi-infinite solid underestimate the magnitude of the maximum vertical stress at the base of the gravel decking. Therefore, a finite element model (FEM) was used to estimate the stress field at the base of the gravel decking. A single equation was fit to the FEM results for a range of gravel depths using a unit load. This equation provides a method for estimating the vertical stress at the base of the gravel decking that is a function of the horizontal distance from the center of the tire contact patch and the total depth of the gravel decking.