An anchor plate is a structural component used mainly in masonry buildings. These plates are connected to a rod or bolt and are typically visible on the outside of the building. The anchor plate distributes the tension created by its anchor point and stabilizes the connected wall. These plates are usually decorated or stylized, as they are visible on the outside of the building. In older buildings, these plates are made of cast or wrought iron and are usually made of steel in modern construction.
The general construction of an anchor plate is the same, regardless of its actual appearance. These plates are wide and flat—the bigger they are, the wider the distribution area. On a residential building, they are rarely more than 2 feet (65cm) across; on a commercial or industrial structure, they may be much larger. In the center of the plate, there is a hole for connecting the tie rod or bolt that penetrates the masonry wall. In essence, the anchor plate is nothing more than a giant washer.
The rod that sits in the middle of the anchor plate completely penetrates the wall behind it. In connects to the inner frame of the building, often hooking directly into the horizontal floor supports. These connectors are placed approximately every 6 feet (2m) on the outside of a building, on every floor. They are essentially what keeps the outer wall of the building attached to the inner frame.
The outer wall exerts a lot of force on the sunken bolt. In order to counteract this stress, the anchor plate distributes the weight of that wall section over a larger area. The wall exerts the same force regardless of the size of the plate, so a larger surface area dramatically drops the pressure exerted on any given area. If the plate weren’t present, the wall would tear itself off the small head of the bolt.
Many anchor plates have an artistic appearance. These plates are extremely functional, but are crafted to look like a decoration. Even still, the plates have several spots where they make firm contact with the side of the building. Often, the plates are symmetrical, so the pressure spots are directly opposite one another. This improves the strength of the plate after the building begins to settle.
The cast or wrought iron used to make anchor plates before the 20th century were used because both of these materials were easy to work with. Cast iron is brittle and wrought iron bends easily, however. Therefore, neither metal was a perfect material. Modern buildings typically have anchor plates made of steel. High-carbon steel has a very similar appearance to wrought iron and is often used to give an antique look to an anchor plate.