Grillages: Testing and making plywood structures

The previous Australian timber design workshops were structured in a manner that divided the participants into 2 streams. One stream following a prescriptive series lectures and tours, the other focused on making a small public building. Doing everything-from design to completion. The ATDW 05 has just one stream-That starts off with three prescriptive days followed by a day of reflection. Participants then embark on building an experimental structure that continues the learning and allows for outcomes to be determined by the participants. Aims of ATDW 05 1. Learning by making extends and enhances design skills to include knowledge of construction and structure. 2. The aim of this experience is collaboration, to discover the sum of many contributions* makes a richer whole. 3. The final aim is to allow a team of participants to take unconditional responsibility to produce a finished product. Introduction-Breaking Timber samples. A. 20 90x35 samples of pine and hardwood where broken in front of participants. Failure mode, sloping grain, density and ultimate load where all discussed on a sample-by-sample basis. Then all the samples where visually graded and the order compared to the order based on ultimate load. There was a good correlation. B. 1 plywood box beam, 1 LVL beam, 1 I beam &1 LVL concrete composite where tested to destruction. During the tests the different engineered timber products where compared. Failure mode and deflection data played key roles in the discussion and discovery. C. Building Plywood Box Beams as part of the fabrication of 2 grillage structures. 1. The first grillage consists of 24 box beams, about 300 x50mm and 2.4 meters long. When assembled they form a simple vaulted grillage capable of spanning 10.5 meters. 2.The second grillage consists of smaller box beams, about 120x20mm and 1.2 meters long, assembled into a 3.6 meter structure and tested to failure. This simple structure took 800 kg before it failed. All participants where surprised at the result. The second grillage was built to demonstrate the behaviour of the grillage system under load-to get a ‘feel’ for the potential loads and spans. D. Building Portal After a discussion and demonstration of portal frame action the participants built 2 small “sheds”. Each shed consisted of 2 portal frames connected by girts and bracing. The connection was a 12mm plywood gusset. Special attention was payed to the design of the nailing pattern and size of the gusset. Each shed was put into the test rig and tested to failure. Both sheds took excess of 4 tonns before failure occurred. In both cases it was the gusset that was the point of failure, which was also the desirable mode of failure. Peter Yttrup provided insightful professional explanation of structural behaviour.