Structural Design Update
Thanks to the generous support of consulting engineers Powell Fenwick, one of our Wikiteers, Darren Kho, has been able to spend an average 8-12hrs a week working alongside three of their engineers. The access to peer review along with all their structural modelling software has proved invaluable in assessing the likely performance of our designs.
Martin Luff and Rachel Wood have been focussed on refining and testing the design iterations of the main structure. This has allowed us to undertake extensive calculations on how the structural frame stands up to both permanent and imposed loads. The permanent load is the weight of the building itself – the structure, cladding and everything else – and the imposed load is what gets added, like your grand piano in the lounge or library of books or loads during maintenance. On top of that, the other main loads are dynamic ones such as snow, wind and seismic (earthquake) loading.
Of highest concern is wind loading, which might surprise some people expecting that seismic loading would be top of the list, especially given the ferocity of some of the quakes Christchurch has recently experienced. However, on a day-to-day basis, a violent storm with loads of snow is more likely to destroy a building.
Because the planned WikiHouse is an exciting shape, with slightly sloping walls and a steep north-facing roof, we have had to do extra calculations in regard to wind loading. The steeper the roof pitch and the apex, the more there are low-pressure areas that form around the apex and the eaves. The difficulty with wind loading is that while it pushes really hard on one side of the building, there is also a corresponding negative or a lower-pressure area on the other side creating a suction (or pulling) effect on the building. Corners are critical for structural strength, and because the WikiHouse design has taken the joints away from the corners, it is crucial to determine the stresses here. We theorised that by taking the joint away from the weakest place in the building, that is, where the main wall elements meet the floor or the roof, the structure will be considerably stronger. Therefore we've designed our own system to transfer the load around those corners. This has been achieved over several iterations developed from our original initial proof of concept model, making our transfer plate different from anything we've seen anywhere else.
Other developments include working to eliminate the central supporting columns within the portal; providing greater adaptability for internal design layouts. This makes the whole building lighter, with lower mass and less foundation requirements. Secondly, it becomes easier and safer for ordinary people to assemble the building. As the portals get lighter, they are easier to handle - it also means less cutting time (cost) and fewer materials.
Although we still have further testing to complete, the initial house could have a clear span of 6.4 metres, by far the longest span achieved by any WikiHouse design to date. This gives us a lot more flexibility in the type of space we can craft, and will be better for such uses as public buildings and schools, which require larger internal spaces.