Wood shrinks in many different directions when it dries out, but it shrinks most along the parallel of the annual rings. It is suspected that purlins were originally placed in the forks of two posts. However, the conventional European building stood on the ground, hence the ventilation tended to be poor. In this case the brackets were mortised into the eaves closer board. During an earthquake, the joints so necessary to wood construction function somewhat like shock absorbers, affording wooden buildings a certain amount of give, which is not possible with rigid stone or brick construction.
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