Behaviour of brick masonry under compressive loading

Abstract

This study presents the results of investigations into the compressive behaviour of brick masonry constructed with cement mortar and mud mortar. For cement mortar, a particular cementsand ratio (1:4) has been used and for mud mortar different percentages of randomly distributed jute fibre and jute mat conforming uniform distribution have been used. Stack bonded prisms of different heights, prisms with vertical joints and wallettes(walls) have been used in the investigation. All the specimens have been tested under vertical compression in the laboratory. The deformation, strength characteristics and failure modes have been analysed and explained in the study. Besides ,two dimensional linear elastic finite element method of analysis has been used to investigate the platen effect imposed on the specimens used in the study. The study reveals that in case of five brick high prism, the effect of platen restraint is substantially minimized. It has been found that the deformation characteristics of masonry can be represented by a parabolic equation of best fit. However, with a minor modification, Saenz's stress-strain relation originally proposed for axially loaded concrete can also be used to represent the deformation characteristics of masonry with good approximation. The study also suggests that the wall(wallette) strength is 0.87 times the strength of five brick high stack bonded prism and 0.75 times the strength of five brick high pr~sm with vertical joint. A theoretical formula has also been proposed from finite element analysis to predict the compressive strength of stack bonded prism. The formula predicts the compressive strength of stack bonded prisms more closely than any other existing formula. Investigation into the mud mortar reveals that jute fibre prevents the formation of crack in mortar bed joints. A limiting maximum inclusion of 1.9% jute fibre results in a maximum increase of unconfined compressive strength of mud mortar by 35.3%. For resistance to lateral deformation the limiting inclusion lies between 1.5% to 2.0%. Above these limiting values the increase of both strength and resistance to lateral deformation are inhibited. The use of jute fibres in the mud mortar has no appriciable effect on the strength of the masonry.