From one of Ellen’s1 projects, a “government anchor”:
We find these in buildings, but not as often as we should. They are representative of a method, feasible using nineteenth-century technology, to tie wood-joist floors to the bearing walls that support them. Those ties brace the walls and also improve the overall structural action of the building by allowing the floor diaphragms to transfer load to the masonry shear walls. (Note that the diaphragms are terrible in most rowhouses and tenements – single layers of plank that are not well connected – but are significantly better in most commercial buildings of the era. Double layers of plank, tongue-and-groove plank, and diagonal plank all provide pretty good flexible diaphragms.)
That’s an iron rod embedded in a collar joint – ideally a joint at the center of the wall thickness, but that depends on how many wythes thick the wall is – with an iron strap wrapped around it. The inboard end of the strap is nailed or bolted to the side of a joist. If the wall starts to move outward, it pulls the joist along with it. If the wall starts to move inward, it pushes on the joist. Obviously, having this connection at one joist doesn’t do much for a whole building, but when we find government anchors, we typically find them at every third or fourth joist at each floor. Also, the whole idea requires that the wall be solid masonry, with the wythes tied together by headers.
Ellen also found a failed anchor:
That’s the strap with its end uncurled and no rod in sight. Given that there’s no sign of gross movement of the wall that is being probed and repaired, and the adjacent anchors were in fairly good condition, it’s extremely unlikely that the rod was somehow ripped out of the end of the strap. The rod might have rusted away completely, but that raises the question of why that one piece of iron rusted so badly while other embedments nearby did not. My pet theory is that this anchor was damaged during the original construction and no one bothered to replace it then. It also could have had the bent end of the strap and rod removed during a previous repair campaign.
Finally, the name. They’re not called “government anchors” because people were complaining that the “government made me do it.” They’re called that because anchors were explicitly required by building codes. Here, for example, is the 1892 New York City code requirement:
- In today’s post, Ellen will appear only as a disembodied hand. ↩︎
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