I do not want to inflame the situation but feel, being as John Napier has tried to be precise ('What's the crack with the cruck?', AJ 29.7.04), that further words need to be written on this matter.
If Mr Napier had read the words of the article (Building Study, AJ 15.7.04) in their entirety then he would have found a more detailed description in the text. To paraphrase directly from the discussed article, the parabolic arch form was created to mimic the function of the traditional cruck frame without the need to source large, naturally curved sections or to use fabricated, homogenised, glulam sections .
The article states that it is a parabolic arch that is mimicking the cruck frame, which in structural and functional terms it clearly does. If, today, 12 large curved trees were commercially available, these would have been considered.
To finally comment on the suggested description of the frame as a fabricated portal frame, this is not correct. As previously stated in the article, the frame is a parabolic arch. Portal frames have thickening at the junctions, which are haunched zones to carry the bend forces around the corners.
This structure can be described as a parabolic arch and uses compression as the primary structural mechanism to support the applied load.
Portal frames use their bending strength to carry the loads.
The Kindersley Centre structure at Sheepgrove Organic Farm is a modern interpretation of a traditional cruck building form. I do not know whether this response is being helpful or inflammatory but trust that it adds to debate, which could be considered as the cornerstone of a balanced society.
Mark Lovell, Mark Lovell Design