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