Forest Investment Account

Abstract of FIA Project Y051078

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Load sharing between log stringers in gravel decked log bridges:

Author(s): Lyons, Kevin
Imprint: Vancouver, B.C. : University of British Columbia, 2005
Subject: Forest Investment Account (FIA), Bridges, Design and Construction
Series: Forest Investment Account (FIA) - Forest Science Program


In this project a Finite Element Program (FEM) was developed for structural analysis of gravel decked log bridges. The FEM included components for modeling the load spread through the gravel decking and the load transfer between the stringers through the lashing. As the length of the bridge decreases the stringers (for a given diameter) become much stiffer; therefore, the lashing stiffness must be increased to maintain load transfer. For bridges less than 12m long the lashing stiffness required for full load sharing increases exponentially. In the case where the middle region of the bridge is between the lashing points and the load is applied at midspan the stringers will act independently in the region where the load will create the greatest bending moment in the bridge. Therefore, a bridge designer could dramatically underestimate the maximum bending stress in the bridge if full load sharing was assumed and a combined section modulus was used in the stress calculations.

For further information, please contact C. Kevin Lyons, University of British Columbia (

Updated September 08, 2005 

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