Tie rod

A tie rod, called gergi demiri in Turkish, is a horizontal bar that links the two supports of an arch or vault. Under load an arch pushes its feet outward; the tie takes that push as tension and keeps both sides locked together. This reduces the need for buttresses or very thick walls, so a span can rest on slimmer piers. Timber ties doing the same job are also found.

Role in the structure

The tie usually sits at springer level, where the curve of the arch begins. Its ends are buried in the wall or pier and secured with a cramp or anchor plate. Ottoman buildings use them widely in arcades, latecomers’ porticoes and large interior arches, which is why thin lines crossing between arches in photographs of historic interiors are most often ties. If a tie is removed or snaps, the arch can begin to spread, the keystone can drop and the piers can start to rotate.

Tie rods in surveys and restoration

The position, section and end detail of each tie are recorded separately in a measured survey, because the tie is part of the structural system rather than an ornament. Where the ends are hidden in masonry, corrosion swells the iron and can crack the surrounding stone. Restoration keeps the tie and, when needed, renews it on the same principle; removing one without understanding its role directly affects the stability of the building. For a wider view of conservation principles, see our article on conserving architectural heritage. In a 3D model ties are small details, yet they noticeably set the sense of scale in an interior view.