Abstract: In the three-dimensional space, the conventional strain state is expressed by three normal strains and three shear strains. Therefore, six strain gauges at least are required to determine the strain state of a point. Based on the strain state theory, a contacting three-dimensional strain rosette that can measure strain in concrete or geomaterials is developed. The device is made up of six strain gauges, and the layout of strain gauges must meet a special condition. According to the relations of components of strain between representations for the conventional strain and the linear strain in an arbitrary direction, transition matrix is built to bridge relationships between the test results and the traditional strain state. Subsequently, the solution qualification is derived and expatiated in order to illustrate the layout of the six strain gauges. The two schemes, namely the orthogonal tetrahedron and the normal tetrahedron, are studied in detail after considering the construction convenience, rational and logical methods are constructed. The tests on the device itself and further on a rectangular shaped sample made of mortar show that the two three-dimensional strain rosette is reasonable and convenient to measure the strain state of concrete, rock and soil in engineering.

Key words: civil engineering, strain state theory, three-dimensional strain rosette, transition matrix, normal tetrahedron shape