The nowadays problems in exploitation of groin vault construction built of the Middle Ages are exiting due to overloading, dynamic vibrations, settlement, as well in-plane and out-of-plane deformations which can cause failure of masonry structures. Safety criteria must be specified by determining deformation limits between interacting parts of groin vault, to prevent emergency situation in heritage buildings. Three-dimensional scanning of arch structure by means of 3D laser scanners has been done and was used for geometric modelling of masonry arch shell. The structures thrust line changes position in cross section and internal forces relocate significantly after the abutment deformations and crack forming in groin vaults. Riga Dome Cathedral has a good example of groin vault in deformed condition which monitoring is esssential and which model has been created using improved rotation mechanism of masonry rib parts and cracks opening measurements. Deformed condition vault model and long term crack monitoring will be used for analysis of the abutments deformations influence. Deformation criteria have been developed for safety exploitation of heritage masonry structures