As the path to innovation was not very successful after the mechanical testing, a more conservative way was chosen. Building variants that fit the Cradle to Cradle criteria such as only technological or biological materials will be compared.
These variants can be compared with a Life Cycle Assessment on environmental impacts. A strict boundary will be needed to compare them with the same functional unit.
The functional unit is 1 m2 roof including:
* boarding, insulation, waterproofing and inside finishing * construction of beams and connections equally distributed over 1 m2
The variants are:
* steel construction with 200mm glass wool insulation and gypsum inside finishing * wood-steel hybrid that can be disassembled or incinerated * wood laminated beam that can be incinerated * wood and natural adhesives that can be composted * massive wood as single material
An interesting variant that can be ad:
* bio based composite with soy oil and flax fibers
The variants are now tested on bending strength. The supporting points are 2.8 meter from each other. The load is spread over two points 0.7 meter from each other.
Variant 1 is the existing reference inspired by the Q-concept. The max load before collapsing is 9350 N. The area is 0,9 m2 so it is more than 1 kN per m2. Also bending is minimal. And collapse is announced by a lot of cracking.
Figures variant 1 during collapse.
Variant 2 was already bending under its own weight. The weak point is the combination of bending and shear force that lets the week point of the connection splice apart. The maximum resistance was 323 N.
Figures variant 2.
The biggest problem with variant 3 was that the bottom flenge gets loose from the web because its own weight. Especially with the dove tails that act like a hinge but also during the second attempt without the dove tail connection is mostly resisted with the web strengths. The max resistance was 833 N.
Material preparation For building the variants some materials were collected. Also cutting big boards and milling the profiles needed some preparation. Below are some pictures of preparation of the materials.
Figures sizing and milling variant 1.
Figures milling variant 2. Figure fitting variant 3. This all came together with 12 students building the three different variants.
A criteria in the design that will be tested is that it is totally biodegradable. This means that no synthetic glue or steel will be used, only wood and straw. Straw plates used in this test are from BCA-Boards and have known properties for structural use. Other properties like moisture effects will have to be taken into account with this material.
The design given has a span of nine meters with a limited height. The roof is a major challenge. So selecting, designing and testing of the roof have first priority. Second priority is the ground floor however that is not dealt with in this test.
Three variants for the roof are designed. Each group of 3 students will work on a different variant.
Variant 1, solid wood
This solid wood construction is manufactured by Inholz in Germany. They say no other materials than wood are used. Pieces of wood are connected with wood pins to make a solid floor prevent different bending of the beams.
Theoretical a span of 9 m is possible. Only to find these wood lengths is difficult. This can be solved by making cold connections. The pieces of wood next to the joint will transfer the load. Profiles like in section A will be available.
Variant 2, I-beam
A common FJI-beam has Kerto flenges and a wood particle board with a glue connection. The space between the beams can be filled with insulation.
This has been transformed to an I-shape without the use of glue. The connection between the straw board web and wood flenge is with a milled dove tail. A factory could mill these profiles very precise. We will have to do it with hand milled profiles which take some time to make it fit. Milling will be done by the Civil Engineering staff.
To connect the flanges an interlocking piece of wood can be placed between the flanges. The resulting cross section is half of the solid wood beam.
Variant 3, curved web
Corrugated steel webs are being used in beams. The thin material will not buckle and is strongly attached to the flanges.
This concept could also be applied with boards. The web can be guided trough a curved groove in the flanges.
A more simple solution is to let the web fit in holes in the flange. This can be made in the factory with milling or laser cutting.
To connect the flanges an overlapping board can be placed with wood pins.
Testing
Pressure will be put on the beams to create a bending moment. The distance it deflects is linear related with the time. Occurring force will be measured.
