EXPERIMENTAL DATA OF FRICTION COEFFICIENT FOR SOME TYPES OF MASONRY AND ITS CORRELATION WITH AN INDEX OF QUALITY MASONRY (IQM)

This study constitutes the results of an experimental investigation into the description of certain types of wall masonry present in traditional southern Italy buildings. The parameter applied is that of the friction coefficient between the joints of the stone blocks which constitute the masonry. The wall-to-wall friction is as important as other mechanical parameters in that it acts on the structural behaviour of masonry with regard to in plane mechanisms and mixed mechanisms (both in plane and out of plane). The friction coefficient provides a useful indication in evaluating the type of masonry and its behaviour to be used in seismic areas. Similar friction values for all types of masonry are reported in literature, while in effect these values vary according to the type of masonry and materials used. The aim of this study is not to provide certain friction values, but a range of acceptable values in relation to the type of masonry considered in the study itself. Experimental investigations which allow the estimation of the friction coefficient associated with failure through sliding, are carried out with a hydraulic jack, coherent with the Mohr-Coulomb failure criterion. Shear strength depend by compression in the wall, so it is necessary evaluate ultimate shear strength (cohesion) in the absence of normal compression. In order to obtain this result, it is necessary to carry out two tests, on two walls belonging to the same masonry type, but subject to differing values of compression. The critical interpretation of the tests provides, for each sample, the experimental values of the coefficients of friction and cohesion as well as will be shown later in this work. A further interesting aspect of this study is the verification of the existence of a correlation between experimental results, and a qualitative judgement expressed through observation of the masonry. To this end, a method well established in literature has been used for the measurement of the quality of the masonry. An index of quality masonry (IQM) is evaluated on the basis of the survey of predetermined parameters that indicate respect for the rule of the art of building (size of the stones, regularity of the texture, quality of the mortar, etc..). This methodology has been applied to the masonry samples used in the experimental investigation, in such a way as to be able to compare the results of the two procedures. This comparison has provided encouraging results, establishing a satisfactory correlation between the qualitative evaluation of the masonry and experimental data.