Interpretation of in-situ shear test for brick masonry: a benchmark study

The determination of the shear strength parameters by means of in-situ shove test is a key issue in the material characterization of unreinforced brick masonry buildings. The wall stress distribution following the removal of the bricks and the mortar joint dilatancy affect the determination of the friction angle and the initial shear strength respectively. A new approach for the definition of the compression in the test unit and the evaluation of the effect of the joint dilatancy on the initial shear strength has been developed. The compression in the test unit is evaluated based on simple formulas which relate the compression stress on the test unit to both the geometry of the specimen and the existing compression on the wall. The joint dilatancy produces an increment of both shear and normal stress at the initial phase of the shove test when the specimen is at low level of compression and at small relative horizontal displacements. In particular, it was observed that the increment of normal stress is due to restrain the tendency of the joint to expand vertically while the brick is pushed. The new approach was validated by means of an experimental benchmark campaign developed at University of Pavia and Delft University of Technology in which specimens made by replicated brick masonry were subjected to triplet tests