1 Sr. Design Engineer, Power Grid Corporation of India Ltd., Plot No. 2, Sector 29, Gurgaon (INDIA)
2 Professor, Civil Engineering Department, Indian Institute of Technology, Delhi (INDIA)

Loading-unloading and reloading stress-strain curves of interlocking grouted stabilised mud-flyash brick masonry under uniaxial cyclic compressive loading are described. Five cases of loading at 0°, 22.5°, 45°, 67.5° and 90° to the bed joints were considered. The brick units and masonry system developed by Prof. S N Sinha was used in the present investigation. The envelope stress-strain curve, common point curve and stability point curve were established for all five cases of loading. A stability point curve has been used to define the permissible stress level in the brick masonry. An analytical model to describe the loading-unloading and reloading response of this masonry system is proposed. The models account for the effect of residual (plastic) strain on the cyclic compressive behaviour. The model predicts the behaviour in terms of the non-dimensional axial stress, s, the non-dimensional axial strain, e, and non-dimensional plastic strain, er. The loading-unloading and reloading curves were found to be adequately modelled by the proposed polynomial functions. A parent polynomial function was modified to generate the different response curves by incorporating transformation factors that were found to be dependent on normalised plastic strains, er. The present model for loading-unloading and reloading curves compares well with the experimental data for all five cases of loading under consideration.

Key words
Interlocking brick, grout, uniaxial, cyclic loading, envelope curve, common point, stability point, reloading curve, unloading curve