AW. FRIED Kingston University
An experimental programme of work to examine the changes in neutral axis position in masonry joints under combinations of direct loads and bending moments was carried out. Piers, two units high, were constructed using four different masonry unit types, cured by covering with polythene for 28d before testing. In the test, the bottom unit was clamped whilst vertical loads at varying eccentricities applied to the top unit enabled the ratio of direct/bending forces to be varied. Deformations were measured either side of the joint at the centre of the unit. A linear change in deformation was assumed to exist across the joint.
The failure surfaces of the broken specimens were examined and are discussed. At failure the tensile deformations were found to be much larger than compressive deformations, the difference increasing as the load on the specimens increased. When the tensile failure stress in the joint is calculated using elastic theory but allowing for different stiffnesses on the tension and compression sides of the joint, this tensile failure stress is found to be very nearly equal to the direct tensile stress determined using the crossed couplet test. Differences occur when simple bending theory with equal stiffnesses in tension and compression are used. Hence, using the simple bending theory appears to be inappropriate under these loading conditions.