The flat jacks technique can be employed to establish the working tension, the breaking tension and the deformability module of a masonry.
The stressing state measurement (with a single jack) is based on the variation of the stension state generated in a zone of the structure through a cut made in the normal direction to the surface.
The tensions releasing causes the cut’s closing detectable by measuring the convergence between the two points symmetrical to the cut.
A specific flat jack is introduced into the cut and the pressure is gradually increased until the convergence previously created is cancelled. In these conditions the pressure into the jack is equal to the pre-existing stress in the masonry, to less than a constant that takes into account the relation between the load jack’s area and the cut’s area.
The convergence measurements are performed by gluing on the masonry metallic plates of a 5mm diameter and employing a millesimal mechanical removable deformometer. For establishing the deformability features, two parallel flat jacks are used (double jacks test); the jacks define an important masonry sample, on which it is performed an uni-axial compression test in normal direction to the substructure, without removing the sample.
The measurements’ bases for removable strain gauge, applied to the sample’s available face, allow to obtain a deformative complete view of the masonry septum in axial and transversal direction. It allows to establish the masonry deformability module.
The proposed test can provide also an estimation of the masonry compressing strength. It is possible, being careful, to approach the examined masonry’s collapse by increasing gradually the load applied by the flat jacks and then, to evaluate the tensile compression strength.
The technique of flat jack test can be cnsidered non-destructive, since when it ends, the flat jacks introduced into the masonry can be removed very easily and the martor’s strata can be easily reintegrated
- Establishing the tension working
- Establishing the deformability features
- Establishing the tensile strength
- Slightly invasive technique
- Eestablishing immediately the test values
- Establishing a security coefficient for the masonry di un coefficiente di sicurezza per la muratura