In November 2018 our company perform structural tests at the British Embassy in Vienna (AT). Single horizontal flat jack and in-place shear tests were performed on the masonry walls.
Single horizontal flat jack test scope is to determinate the in-situ compressive stress in an existing masonry wall by inserting a thin, bladder-like flat jack into an appropriate slot cut in the mortar around the bricks.
The operator pressurizes the flat jack by pumping oil through a high-pressure circuit; at each pressure increment, the operator records the distance between each pair of gauge points, previously attached on the masonry above and below the wall cut. This is done until the initial stress conditions — before the wall cutting was made — are restored.
The in-place shear test is used instead to provide an index of the horizontal shear resistance of the mortar joints in the masonry. International standards describe three methods to carry out the test: here is used Method C, consisting in the insertion of a small flat jack into the head joint at one end of the test unit (ASTM C1531-16). The operator increases the pressure on the flat jack until a brick cracks or slips; at that point, the maximum pressure is recorded.