Geokon 4000 Series, Инструкция по эксплуатации

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8
Consider the example of an I-beam shown in Figure 6A.
Figure 6A - Strain Gages Mounted on Central Web measures Axial Strain and Bending
Moments about both XX and YY Axes
Four strain gages (1, 2, 3 and 4) are welded in two pairs back to back on the central web.
The gages are at a height (d) above the center of the web (axis yy) and at a distance (2c)
apart. The I-beam has a flange (2b wide) and a web (2a deep).
The axial stress is given by averaging the strain reading from all four strain gages and
multiplying by the modulus.
Equation 1 - Axial Stress Calculation
The stress due to bending is calculated by looking at the difference between pairs of gages
mounted on opposite sides of the neutral axis. Thus the maximum stress due to bending
about axis yy is given by:
Equation 2 - Stress due to bending on Axis yy
The maximum stress due to bending about axis xx is given by:
Equation 3 - Stress due to bending on Axis xx
Equation 4 - Maximum Stress
In all of the above calculations pay strict regard to the sign of the strain.
AXIS YY
AX IS X X
2 a
2 b
1 2
2c
d
3 4
 

   
axial
=
4
1 2 3 4
  
 
   
max imum axial xx yy
  
   

   
yy
b
d

  
 
1 3 2 4
2

   

   
xx
a
c

  
 
1 2 3 4
2
