Images via Contemporist
Have I mentioned that I love wood as a building material? If sustainably harvested it provides a strong, beautiful material that can last for centuries and sequester CO2 the whole time. People have built bridges from it forever, but in such exposed circumstances they don't last forever.
But now there are better wood preservation techniques, and Kris De Decker of No Tech Magazine points us to a lovely new bridge in the Netherlands, purported to be the first wooden bridge in the world that can support the heaviest load class of 60 tons.
it's prefab too!
Spanning 105 feet and rising more than 50 feet in the air, the structure will serve as a grand entrance to the city of Sneek. The €3.5 million bridge was commissioned after a 2005 design competition, and is designed by OAK Architects (a collaboration between Achterbosch Architectuur and Onix architects) and constructed by German firm Schaffitzel Holzindustrie.
It is made from Accoya Wood, where source-certified sustainable species, including FSC certified wood, is treated by acetylation. The supplier, Titan Wood, writes:
Acetylation effectively changes the free hydroxyls within the wood into acetyl groups. This is done by reacting the wood with acetic anhydride, which comes from acetic acid (known as vinegar when in its dilute form). When the free hydroxyl group is transformed to an acetyl group, the ability of the wood to adsorb water is greatly reduced, rendering the wood more dimensionally stable and, because it is no longer digestible, extremely durable.
It is neat stuff, enabling locally sourced woods to be used outdoors without toxic treatments or importing tropical hardwoods. It is a stretch to call it a "new wood species" like the supplier does, it's a treatment.
But if it makes local, sustainably harvested wood more durable then teak, it has a bright future.
New Brunswick, Canada
The old way of protecting a wood bridge was lovely, but the new way is more elegant.
More at Contemporist and No Tech Magazine
UPDATE: Robert Rapier of the excellent R-Squared Energy Blog is Engineering Director for Accsys Technologies, which owns Titan Wood. He explains how it is made and how it works in much greater detail than the website, and answers a lot of questions, at Carbon Sequestration in Practice . He writes:
In a nutshell, Titan Wood chemically modifies fast growing softwood species like (but not limited to) Radiata pine in a way that results in their performance characteristics being superior to some of the best tropical hardwoods such as teak. It is important to note that the modification we make is at the molecular level; we do not impregnate the wood with chemical preservatives that can leach out into the environment.
More on Modern Wood Construction
Wood Construction vs Deforestation
Wood Construction Scales Up
Forest Research Center is Built, Logically, of Wood
School Built From Wood By Sheppard Robson
FMO Tapiola: Prefab Wood Office Building in Finland
Waugh Thistleton's Timber Tower