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(a) FL2R (Proposed EZR) (b) FL2L (LRFD EZR)
Figure 3.27. Comparison of ends FL2R and FL2L.
Figure 3.25. End VA1R after bearing failure.
The corresponding image, Figure 3.30, shows the shear
the girders to contain only half the amount of shear reinforce- cracks experienced by End FL2R just before the loading was
ment requested, leading to the premature failure of the ends stopped. The figure illustrates how the shear cracks form in
in shear. One girder was observed to contain half of the spec- the opposite direction as the end zone cracks.
ified shear reinforcement when it burst in shear failure. How- End FL1L unexpectedly failed in shear due to the lack of
ever, the girder that was tested first did not fail, keeping the adequate shear reinforcement. Images of the shear failure are
reinforcement hidden, so it is only assumed that it also con- shown in Figure 3.31. One can see how the prestressing force
tained half the specified shear reinforcement. In most cases, pulled the bottom flange in toward the center of the girder
the design capacity of the specimens was more than the test once there was no web to resist it. This is the same force that
setup could apply. The team decided to continue with test- pulls on the web of precast girders causing end zone cracking.
ing and use the first half of the load versus deflection curves Once the reinforcement had been exposed, the team was able
to determine when the girders would fail. to calculate the theoretical shear design capacity for the girder
Figure 3.29 shows the load-deflection curve for End FL2R. to be around 700 kips. The experimental failure point was still
The loading of this end had to be stopped before failure greater than the calculated shear capacity value.
because the three hydraulic jacks had reached capacity at
1,200 kips. However, it can be inferred that if more load
3.2.5 Full-Scale Testing Conclusions
had been applied, the test values would have risen above the
experimental values. The full-scale tests on eight full-scale girders has indicated
that end zone cracking due to prestress bursting forces does
(a) FL1L (FL Typical EZR) (b) FL1R (FL Modified EZR)
Figure 3.26. Support with roller. Figure 3.28. Comparison of ends FL1L and FL1R.
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1200000
1000000
Load (lb)
800000
600000
Capacity Using
Capacity Using Estimated
Estimated Values
Values (1,195
(1,195 k) k)
400000
Capacity Using Measured Values (1,229 k)
System Capacity (1,200 k)
200000
Load vs. Deflection
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0
1
Deflection (in)
Figure 3.29. Load versus deflection curve for End FL2R.
not cause a reduction in the structural capacity of prestressed
concrete girders. The orientation of the diagonal cracks is
nearly perpendicular to the forces caused by diagonal tension
(i.e., shear). When external loads are applied, they induce
compressive stresses across the bursting force cracks, and
therefore the types of cracks are not cumulative to each other.
Even when end zone cracks were induced in the testing that
were significantly larger than cracks commonly observed in
practice, there still was not a measurable reduction in struc-
tural capacity. All specimens had capacities at or higher than
the expected theoretical capacity.
When repairing was performed with epoxy injection in an
attempt to restore concrete tensile capacity across the cracks,
there was no significant change in capacity between repaired
(a) General View
(b) Close View Showing Relative
Movement of the Bottom Flange
Figure 3.30. Shear cracks on End FL2R after loading
was stopped. Figure 3.31. End FL1L after failure, east side.
