Very often arches are used for effect in places where sufficient abutments cannot be provided to resist the thrust of the arch. In such cases one or more steel beams should be placed in the wall just above the arch, with the ends resting over the vertical supports and an empty joint left beneath the centre of the beams. The wall above can then be built on these beams, leaving the arches with only their own weight to support. The additional weight which the beams carry to the abutments also greatly increases their resistance to a horizontal thrust. The beams should also be provided with anchors at their ends, with long vertical rods passing through them, to tie the wall together.
Wherever segmental arches are used it is always a safe precaution to place steel rods back of them to take up the thrust of the arch while the mortar in the abutments is green.