The reason gages ST1 and ST3 did not record a rapid increase of strain as did gage

ST2 was due to their location. Gages ST1 and ST3 were located close to the load plates

that provided confinement to the surrounding concrete. The confining effect of the load

plates was much higher close to the load points and decreased away from the load points.

At the mid-span location that was located the farther from the load points than any other

point inside the constant moment region the effect of the load platens was much smaller.

The confinement from the load plates restrained the tensile lateral expansion of the

concrete and reduced the lateral strains at the two locations close to the load points.

 160
 140
 s 120
 S100
 S80o
 so
 3 60
 H 40 -A-ST1 -B-ST2 -e-ST3
 20
 0
 0 1000 2000 3000 4000
 Top Poisson Strain (microstrains)

Figure 4-19. Transverse expansive strains for control beam

 The strain gages attached to the top of both beams in the transverse direction were

able to detect the impending concrete failure as the data from gage ST2 indicated.

However the peak strains recorded by gage ST2 for the control and tube beams were

significantly different in magnitude. The peak strain of the control beam was

approximately 3170 tE while the peak strain for the tube beam was 2230 tEs. That

difference can be explained by the presence of the CFRP grid tubes. As the concrete tries

to expand laterally, due to the Poisson effect, the CFRP grid tubes restrain and resist that