The hole drilling technique for on site deduction of the stresses states in stone masonry by using eight strain gages

The hole drilling technique for the on site deduction of the stresses in structural elements of cultural heritage structures has been applied on two monuments: the Saint Jakobs Church (Leuven, Belgium) and the Cathedral of Tarazona (Zaragoza, Spain). The adjustment of the technique becomes an experimental methodology very different from the one employed for the deduction of residual stresses. There are two main differences in the experimental methodology: the experimental dimensions are thirty times greater and eight strain gages are placed instead of three. The latter is done to have sufficient redundancy in the system and to be able to make an objective analysis of the quality of the results. The paper basically deals with the derivation of the stress states from the strains caught by the eight strain gages in agreement with the general methodology of the hole drilling technique.