Springer

A springer, üzengi taşı in Turkish, is the first stone of an arch, set directly on top of a pier, column or capital where the curve begins. Its bottom face is flat, while its upper face is cut at an angle to follow the arch. The horizontal line where the arch starts is called the springing line.

How the load travels

The compression running through an arch arrives at the springers at each end. The springer takes this inclined force and passes it into the vertical support below. This is where the load changes direction: the inclined force along the arch becomes a vertical load and a horizontal thrust on the pier. So the springer both starts the geometry of the arch and ties the load into the support. It is often a larger and stronger stone than the other voussoirs, and in some buildings it is extended into the adjoining wall.

• Pier, column or wall: the vertical support
• Capital or impost block: the element that spreads the load
• Springer: the first stone of the arch
• Voussoirs and keystone: the rest of the curve

Survey and 3D modeling

The level of the springing line is one of the most important references in surveying an arch. Span and rise are measured from it, and a difference between the two springing levels can show that one support has settled. In an arcade, comparing all the springing levels helps to map how damage is distributed. In a 3D model, setting the springing line as its own reference plane makes it easier to build the arches at the right height.