The effect of local rebar geometry on global strain measurements in pull out tests.

Strain gauges are the common means to measure local strains in structural elements. It is well known that the strain at a given coordinate on the boundary of a structural element depends on the geometry, boundary conditions, loading system, and material properties. The precise location of the strain gauge along a line is not considered critical to obtaining a quality strain measurement at a specific location, wherever a continuous variation of strain along this line is expected, and a slight deviation of the gauge location will yield similar measurements. In a recent study, precise measurement of the circumferential strains on the outer face of cylindrical concrete specimens was carried out during pullout of a central rebar. Analyzing the measured data indicated that a slight shift in the strain gauge location on the order of millimeters only may considerably affect the measured strain. These controlled pullout tests highlighted the pronounced effect of the relative distance between the rebar rib and the strain gauge location on the strain magnitude and its variation with the increasing slip. This effect has not been reported before. It means that a slight difference in the strain gauge location yields different strain–slip relationships. This new finding may affect the interpretation of the measured strains. Attention should be given to the exact strain gauges' locations and detailed rebar ribs locations to properly interpret the measured data. [ABSTRACT FROM AUTHOR]