Different material

Springers whose material is different from the rest of the voussoirs usually have this attribute due to their nature of structural interface between the vault and the site fixation. In the case of the Armadillo Vault, the springers are made of steel as they are required to hold the tensioned force exerted upon them by the thin tension ties; if made of stone, steel ties would eventually break cause cracks under this point pressure. The CorkVault Aarhus is built in the open air, and “given that the cobbled stone pavement should not be affected, a temporary springer was constructed from light concrete blocks held to the ground with 150mm metal poles stuck in the earth between the stones” (Azambuja Varela and Merritt, 2016, p. 774), as the cork blocks would not resist the pole pressure.