Thanks, that looks like it may be a useful starting point. I was hoping someone may have already done some work on an arch structure. I need to work out lateral forces needed to support the arch from collapsing in on itself. Modelling unstructured stone and mortar masonry will be difficult but the first question is using a solid stone support pillar: how wide does the base area need to be to prevent it tipping over due lateral forces of the arch.
This is hard stuff with FEM alone. I think you need graphic statics too.