Light Prestressed Segmented Arch (LPSA) Bridges: A Demonstration of Sustainable Engineering

A jointing method combining slide-fitting with tension-induced compression is presented in this paper. It eliminates the “analysis black box” at each node of a timber structure. Mathematical and computational modeling is further enhanced by the use of small diameter timber (SDT), due to its more predictable natural growth-ring structure. This is the core concept of the LPSA (light prestressed segmented arch) structural system as applied to timber-in-the-round. It represents a significant leap forward in the sustainable use of timber in construction, offering a sustainable alternative to steel and concrete, especially for bridges. The slide-fitting jointing mechanism produces a unique property of harmless distortion energy dissipation via internal rigid-body motion. Therefore, LPSA structures have inherent resistance to the actions of earthquakes, hurricanes and flooding. The LPSA outlines a framework for an urgently needed research, design and innovation field of sustainable engineering, in a world on the verge of environmental instability. SDT is a vast, untapped, sustainable resource. Its use as a premium construction material could provide a recipe for saving what remains of the world's forests and for profitable sustainable development. Two 19,5 m LPSA bridges have recently been constructed, using black locust (robinia pseudoacacia) SDT. This is a least desirable but decay-resistant species with two-to-three times the crushing strength of concrete.