Here Mr. Bresler refers to the safety factor. However, they have no real commercial value or structural use. Changing this reality would lead to environmental, economic and technological breakthroughs of global dimensions. Model Wooden Truss Bridge Students in the Civil Engineering Program down under build this bridge as part of their curriculum. Information A nice list of timber bridge resources.
Links Here is a company that designs timber bridges.
They also provide a nice list of resources. The publications in this list present results of Forest Products Laboratory research. These publications were written to facilitate application of new and existing technologies. PO Box 1002 Millersville University Millersville.