R.C.DE VEKEY and J.S. SKANDAMOORTHY Building Research Establishment

The flat jack is a flat flexible envelope which is filled with hydraulic fluid and can be pressurised using a pump and used to generate small movements in structures and apply substantial forces. Suitable arrangements allow the measurement of compressive stress in members and the local stress strain behaviour with minimal, easily reparable damage of the masonry. Flat jacks are most accurate if they are of comparable size to the masonry units but this is often impossible in stonework with large dressed stone blocks where insertion of such large jacks would have safety implications. The paper describes some calibration trials using jacks of various sizes in a sandstone block wall.