Appendix H.Two Strain Gauges Mounted One Above The Other

Where only one surface of the straining member is accessible, you can use two strain gauges, one weld-mounted above the other, to separate axial strains from strains due to bending.

 

Figure 22: Two Strain Gauges Mounted One Above the Other

E₁ and E₂ are two measured strains at distances d₁ and d₂ from the neutral axis of a steel member (e.g., a sheet pile).

Note: E₂ must be welded onto E₁ 

If R = d₂ / d₁ then:

The Axial Strain along the neutral axis = (RE₁ – E₂) / (R–1)

The Bending Strain at a distance d₁ from the neutral axis = (E₂ – E₁) / (R–1)