Uniaxial Load
The arrangement shown below, for a centrally loaded column or tension member, is somewhat more complex.

Uniform uniaxial stress, with Poisson gage orientation:

It can be seen from the figure that the bridge currents change with applied strain, and thus the output voltage is a nonlinear function of strain even before calibrating with a shunt resistor. Because the nonlinearity is different in tension and compression, separate calibration equations are required as follows:

To simulate compression in ,

(514.30)

And, for tension in ,

(514.31)

Equations (514.30) and (514.31) provide for correctly simulating the longitudinal surface strain in compression and tension, respectively, at any strain magnitude. In common with the corresponding half bridge, the instrument indication at the calibration strain level is precise, but operation at a different strain level will introduce a small error due to bridge-circuit nonlinearity. When necessary, the corrected strain can be calculated from [see Eq. ( 514.18 ) for notation]:

(514.32)

Page 41 of 50