Pendontive type of hammer-beam. Early sixteenth century.
hammer-post is, really, the weak part of the whole construction, the strength of the latter being invalidated by the insertion of three tenons from the principal, the purlin, and the main tie-beam, the three-inch tenon of the beam being taken through the hammer-post to the principal at F. The small tie-beams, G, inadequate as they appear, are strong enough to correct any tendency in the hammer-post to bend in the lengthwise direction of the roof, which might occur owing to the enormous downward strain upon it, even when partially relieved by the upward pressure of the principal, carrying, as it does, nearly the whole of the superimposed weight of the roof.
Actually, in spite of the rake of the principal and the common rafters from below the clerestory down to the walhhead, there is little, or no outward thrust from this roof.
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