was approximately 2550 [E which was approximately 10% lower than the strain recorded
for the control beam.
160
140
S120
3 100
80
7g 60
S40
2 0-Si -SA- S2 -8-S3
20 <-S 4 E- SS5
0 1000 2000 3000 4000
Compressive Strain (microstrains)
Figure 4-16. Load-strain curves for control beam
The compressive strain for the extreme concrete fiber can be calculated by plotting
the strain profile (see Figs 4-17) of the beam. Assuming a linear distribution of strain
through the beam cross-section a straight line can be fitted and the equation of the fitted
line can be used to determine the strain at the extreme concrete fiber. The fitted lines
were in good agreement with the experimental results as it was evident in Figs 4-17. The
average R2 value (the proportion of the variance in y attributable to the variance in x) of
the fitted lines for the tube beams was 0.999 which was close to a perfect match (R2 = 1).
This was typical for both the control and tube beams. The high R2 values support the
assumption of a linear distribution of strain through the beam cross-section which also
suggests that plane sections remain plain.
The strains at the extreme concrete fiber in compression at increasing load levels
were calculated based on the fitted line equations and are presented in Table 4-3. The
strain at the extreme compression fiber at peak load (crushing strain) for the control beam
was approximately 3170 tE whereas for the tube beam was 3010 tE. The crushing strain