Deformation characteristics of brick masonry due to partial unloading

Experimental investigation into the behaviour of half-scale brick masonry panels wereconducted under cyclic loading normal to the bed joint and parallel to the bed joint. For each cycle, fullreloading was performed with the cycle peaks coinciding approximately with the envelope curve.Unloading, however, was carried out fully to zero stress level and partially to two different stress levels of25 percent and 50 percent of peak stress. Stability point limit exhibits a unique stress-strain curve for fullunloading but it could not be established for partial unloading. Common point limit was established for allunloading-reloading patterns considered, but its location depends on the stress level at which unloading iscarried to. Common point curves were found to follow an exponential formula, while residual strainsversus envelope strains can be expressed by a polynomial function of a single term. The relation betweenresidual strain and envelope strain can be used to determine the stress level at which deterioration due tocyclic loading began.