Home Grown stacked plank elements
The Business Challenge
This project came about through the development of an offsite manufactured service core, the e.Core by David Blaikie Architects. The e.Core would use home grown timber which would be formed into massive timber panels and be capable of being manufactured easily by semi-skilled workers using innovative construction methods. It would need to be robust enough to be transported to site and carry vertical loads and provide racking resistance for the dwelling in which it would be used. Nailed brettstapel, or stacked plank, was chosen as it fulfilled all the above requirements. It comprises low grade C16 timber planks fixed together with nails to form a solid timber panel, thereby adding value to the timber. The manufacturing process was monitored and evaluated so that lessons learned could be passed on. Structural properties of the panels and the nails which were used to manufacture them were found through testing to check the behaviour.
The timber used was Scottish grown Sitka spruce supplied at Grade C16 but in addition was acoustically sorted using a Hitman HT2000. This equipment uses the relationship between timber density and the speed of sound to provide an alternative means of classifying the strength of a piece of timber. This was carried out on all the test pieces but the timber strength was allocated using an average density for the whole sample.
Eight no. timber stud wall panels were manufactured by MAKAR 2.40m high x 2.34m long panels sheathed with OSB3 as per the specification supplied and tested in accordance with BS EN 594:2011.
Bending tests were conducted in accordance with BS EN 408 to investigate the behaviour of a basic panel in order to validate the acoustic sorting against the stated grade. In addition point load tests using 3 point bending were conducted in order to investigate the lateral load spread capability of the brettstapel panel both with and without a sheathing layer. A deck would however be required if a Brettstapel panel is used as a floor element in order to enable diaphragm action for whole building stability or as an airtight layer for external panels. Two separate test series were conducted: one with steel nails and one with aluminium nails. The 4 point bending tests resulted in values for global MoE only due to inadequacies in the test equipment but reasonable correlation was obtained with the acoustic sorting. This however gave MoE values lower than the stated grade on the CE mark. For the 3 point bending tests all the specimens failed at the planks immediately under the load head with a tension failure on the bottom face.
It is rare to find engineers who think creatively, innovatively and are able to communicate so effectively as to assess our obstacles, perform research and provide answers for our business. - MAKAR Construction
Related Project: Solid Timber
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