This paper presents results from experimental research into the composite construction of manufactured timber beams and unseasoned natural round logs with concrete. The authors, engineer Peter Yttrup and architect Gregory Nolan, are engaged in collaborative research to prolong the service life of timber bridges. This technology presents considerable benefits for bridges and for the construction of buildings. As timber is a natural material, exposed timber structures such as bridges biodeteriorate when environmental moisture enters the timber. To slow this process, a concrete deck can be introduced to act as a waterproof membrane and, if a suitable shear connection system can be included, a composite structural element with the timber beams.
Composite action stiffens the bridge while the exclusion of water greatly extended the service life.
In building design, CET systems offer performance and construction benefits. The concrete enhances the thermal and acoustic performance of the timber, while the timber is lighter and easier to work and fix than other similar systems. The research has shown that timber and concrete can be used together with increasing levels of cost, performance and sophistication. The simplest form of CET arrangement tested was a series of logs butted next together then overlayed with concrete. Various methods of shear connection between the materials were tested for effectiveness and ease of construction.