Titan Wood of the Netherlands is promoting a revolutionary lightweight yet strong acetylated wood in the Arabian Gulf.

Called Accoya, the wood was used in the construction of the world’s first wooden heavy traffic bridge, which has just been completed in the Netherlands.
“Accoya wood is produced using a revolutionary wood modification technology — wood acetylation — which further enhances the superb qualities of wood. It is produced using a non-toxic process which effectively converts certified sustainable solid softwood lumber into what is best described as a ‘new wood species’ via acetylation,” says a spokesman for Titan Wood.
“Accoya wood weighs only 510 kg per cu m, which makes it twice as light as many tropical hardwood species. This strength-to-weight ratio, accompanied by the exceptional dimensional stability of this revolutionary wood, makes it possible to create large constructions, such as the bridge in Sneek, which are both classically beautiful and reliable in even the harshest of environments,” he says.
The 60-tonne-class heavy traffic bridge, known as ‘Akkerwinde’, has a free span of 100 ft, measuring 50 ft high and 45 ft wide, and has been designed to meet the heaviest traffic requirements. The bridge, located 125 km northeast of Amsterdam and providing a future connection across the A7 motorway, a major Dutch thoroughfare.
Accoya wood, the acetylated wood specified in the project, is a FSC (Forest Stewardship Council)-certified modified wood with the qualities of tropical hardwoods and proven constructional value.
“Unlike most tropical and European hardwoods, its colour does not degrade when exposed to ultraviolet (UV) light, making it particularly suited to exterior applications where performance and appearance are valued. Moreover, the Accoya wood production process does not compromise the wood’s strength or machinability. The combination of UV resistance, dimensional stability, durability, its reliability (in terms of consistency of both supply and quality) and retained strength means that Accoya wood offers a wealth of new opportunities to architects, designers and specifiers,” he says.
For the Sneek bridge, Titan Wood supplied more than 400 cu m of acetylated wood created from certified Radiata Pine. The 12-m steel roadway is supported by two identical wooden trusses bent to resemble a medieval arch. The pair of angled outer rods are approximately 1.10 m thick and are separated in the centre by a bearing consisting of three-layered interwoven rods of the same girth.
Each of the 30-m girders measure 1.10 by 1.40 m and weigh nearly 24 tonnes. Moreover, the four outer pressure arches (1.08 by 1.20 m) and all diagonals are twisted into the intertexture. The bearing is singly arched. The inner pressure arch has a radius of about 21 m. The connection at the top of the bridge is realised with a 12-tonne steel hinge featuring two steel plates with a thickness of 10 cm, a height of 1.5 m and a length of 5 m.
“Accoya is stable in form, which allows working details in such heavy wooden bevelled construction. When the construction is suspended, some 80 to 100 tonnes of power are released,” says Emil Lüning of Lüning Engineering, which served as overseer for the construction of the wooden aspects of the bridge. For this innovative application, Titan Wood supplied 38 mm planks and transported them as rough wood to Germany where the construction firm Schaffitzel Holzindustrie glued, planed and sanded the wood according to the specified bend and torsion.
Lüning adds: “For constructional reasons, we decided to laminate the wood in two phases. The acetylated planks are first machined into beams of 1.08 m height, which are rip-sawed into 60-mm-thick planks with a width of 1.08 m. Then they are glued in another direction and formed into straight, curved and twisted beams measuring 1.08 by 1.40 m.” All of the structural elements were assembled with 48 mm threaded rods, which were secured into the wood by way of injection with epoxy glue.
The SHR, an independent timber research institute, in Wageningen, Netherlands, carried out extensive research to verify the validity of this method of gluing. The strength of connection was then extensively tested by the Technical University Eindhoven under the direction of Professor André Jorissen.
Jorissen explains: “Considering the fact that the bridge was to be constructed with a new material, it was better to be on the safe side. Safety is now guaranteed by meeting all current requirements of strength. Standardised test programmes gave a good picture of new aspects which then could be established.”
Additionally, to maximise the life span of the acetylated wood, it was coated with a protective coating which will combat harmful UV rays.
All of the materials were assembled prior to the bridge construction to ensure that no detail was left undone. The bridge components were delivered to Sneek in kit form and were assembled at a site 2 km away from its final destination. The construction was then transported to its final destination, raised into place via crane, and attached to the steel roadway. Construction was recently completed and the bridge opened to traffic last month.
Elaborating on the advantages of wood as a construction material, the spokesman says: “Against a backdrop of growing concern about the environmental impacts of the materials we use, the popularity of wood is set to increase. Created by nature to be both strong and beautiful, wood offers warmth, character and endless design possibilities. However, it’s not just good looks and charm that will ensure a leading role for wood in our future, but a number of other reasons as well, including: the fact that it is a non-toxic, recyclable raw material; is light, yet strong and easily worked; offers good sound absorption properties, is a truly sustainable resource for construction, is a natural insulator and, as such, reduces energy use and reduces the effect of global warming, as trees and wood products act as carbon sinks.