Geokon 4911, Руководство по установке, Страница: 18 / 27

12
Because of the difference in these two coefficients, a correction is required to the apparent
strains, equal to the difference of the two coefficients. The equation for this correction is as
follows:
ε
load related = ((R
1
- R
0
) × C) + ((T
1
- T
0
) × K)
Equation 3 - Load Related Strain
Where;
T
0
is the initial temperature recorded at the time of installation.
T
1
is the current temperature.
K is the thermal coefficient from Table 1.
The strains thus calculated are due to load changes only.
Using the same theoretical example from Section 4.1, where R
0
= 8000 digits on channel B, and
R
1
= 7700 digits on channel B, with the addition of temperature, T
0
= 20 °C and T
1
= 60 °C
(during the concrete curing); the strain corrected for temperature (i.e. due to load changes only)
can be calculated as follows:
ε
load related = (7700 – 8000) 0.343 + (60 – 20) (12.2 – 10) = – 14.9
µ
strain (compression)
Please note that the actual strain undergone by the concrete, (e.g., that which would be measured
by a tape measure,) is given by the formula:
ε
actual = ((R
1
- R
0
) × C) + ((T
1
- T
0
) × K
steel
)
Equation 4 - Actual Strain
Apparent strain =
(7700 – 8000) x 0.343 = – 103 µ strain (compression)
Load related
strain =
(7700 – 8000) x 0.343 + (60 – 20) x (12.2 – 10) = – 15 µ strain (compression)
Actual strain =
(7700 – 8000) x 0.343 + (60-20) x (12.2) = +385 µ strain (tension)
From the above example, it can be seen that while the concrete was actually expanding by 385
microstrains due to the temperature increase, the apparent strain was 103 microstrains in
compression, and the actual change of strain due to increased stress in the concrete was only 15
microstrains compression.