Historic Structural Detail: Cast Iron, Hiding In Plain Sight

by Don Friedman on January 7, 2016

More from Tuesday’s site visit. At another opening in an interior bearing wall, we had an interesting-looking lintel (click to enlarge):

IMG_1221

First, some clarifications about this picture. The main opening, at the bottom, is original. The smaller opening above it (at the green arrow) was a later alteration, probably to pass a ventilation duct through the wall. The yellow line is a temporary power cable.

On to the actual topic: The lintel is visible (at the red arrow) as a thick plate of meal with a rough surface. It could, in theory, be a steel plate but (1) steel plates were not typically used as lintels in the 1890s and are still rare today and (2) that would be a very thick plate for building use in that era.

What was in common use for lintels in bearing walls in the 1890s? Brick jack-arches, which this is not. Brick jail-arches in combination with a wood lintel, which this is not. One-piece stone lintels, which this is not. And cast-iron inverted Ts, which…jackpot! The third edition of Architectural Iron and Steel, by William Birkmire, had illustrations of the various shapes of iron lintel in 1903:

Architectural Iron and Steel 3e - William Harvey Birkmire (dragged)

Lintel elevations are on the left and cross-sections on the right. After the iron lintel was laid on top of the opening, brick would be built up around the vertical web (see figures 1 and 2), leaving only the bottom flange exposed.

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