Innovation in flat-jack application to evaluate modern high-strength hollow concrete block masonry

Abstract

Flat-jack testing is considered efficient in the analysis of historical masonry built with stones or solid bricks. The advantage of this technique is obtaining important properties to a structural analysis, such as the stress-strain curve of the wall, masonry modulus of elasticity and an estimate compressive strength, without any permanent damage to the structure. Due to its advantages, the technique could also be applied in modern masonry, but the current available equipment has limitations in its geometry and maximum applied pressure. This paper presents the development and application of a new flat-jack equipment, that can fit hollow blocks and allow applying high pressures of more than 20 MPa, way more than the usual flat-jack limit of 5 to 7 MPa. The developed flat-jack was used to test hollow concrete-block masonry to evaluate masonry strength and elastic modulus values, that were compared to values obtained from destructive testing also performed. A good correlation on both results was observed. Based on the experimental results and using the Abaqus FEM package, a detailed micro modelling is presented considering the masonry units, mortar and their interfaces. The numerical model was able to successfully capture crack pattern and strain and stress distribution of the walls in good agreement with the experimental results. Both on the experimental and numerical analyses the testing procedure on where to clean the mortar joints, on the top-bottom of the tested area or also at the lateral vertical joint of the region, was assessed. Result indicate the success and validation of using flat-jack application in modern high-strength hollow block masonry, as far as we know for the first time, and point suggestions on were the cut the mortar joint before testing.