Numerical Investigation on the Use of Flat-Jack Test for Detecting Masonry Deformability

Abstract

Correct determination of masonry deformability is fundamental for evaluating the seismic response of masonry structures. For existing buildings, double flat-jack tests are largely used to estimate elastic modulus, but many problems arise for a reliable interpretation of the test outcomes. Formulas provided by standards or available in the literature follow different approaches, the results of which are strongly variable. Furthermore, these formulas do not take into consideration important practical aspects of the test apparatus, like the position of the measurement reference points in the masonry sample. The arrangement of the gauge points can influence the displacement measurements and, consequently, the value of elastic modulus. This work aims at numerically investigating-through finite element (FE) models-the effects of the position of the gauge points on the outcomes of a double flat-jack test. In particular, a continuous FE mode is adopted, in which the concrete damage plasticity model implemented in Abaqus code is used to model the nonlinear behavior of the masonry. This study provides recommendations on the correct way to determine reliable values of elastic modulus from double flat-jack testing. Furthermore, numerical results and their comparison with experimental data allow for important considerations with regard to both the research field and professional and practical activities.