In November 2018 our company performed structural tests at the British Embassy in Vienna (AT). Single Horizontal Flat Jack tests and In-Situ Shear Tests were performed on the masonry walls.
The purpose of the Single Horizontal Flat Jack test is to determine the compression stress in place in an existing masonry wall by inserting a thin bladder-shaped Flat Jack in a special slit obtained in the mortar around the bricks.
The operator pressurizes the Flat Jack by pumping oil through a high pressure circuit; at each increase in pressure, the operator records the distance between each pair of reference points, previously fixed on the masonry above and below the cut in the wall. This operation is carried out until the initial stress conditions are restored, before the cutting is carried out in the wall.
Instead, the Shear Test is used to provide an index of the Horizontal Shear Resistance of mortar joints in the masonry. International standards describe three methods for performing the test: Method C is used here, which consists of inserting a small flat jack into the head joint at one end of the test unit (ASTM C1531-16). The operator shall increase the pressure on the flat jack until a brick cracks or slips; at that point, the maximum pressure is recorded.
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