Alternative Support Systems for Cantilever - National Transportation ...

5.2.1 Behavior of Specimen During Testing
5.2 Torsion and Flexure Test
The second test comprising of both flexural and torsional loading was conducted on
January 6, 2010 at the Florida Department of Transportation Structures Research Center. There
were concerns with bolt slippage due to both the flexural and torsional moment arm connections.
Prior to testing, the system was loaded with the crane only to remove some of the initial rotation
due to bolt slippage (See Figure 5-8). During testing, the test specimen was loaded at
approximately 100 pounds force per second and the formation of cracks on the surface of the
concrete was monitored. At approximately 10.8 kips, bond between the concrete and the
embedded pipe loosened, causing a change in stiffness. At approximately 14.3 kips, flexural and
torsional cracks began to form on the concrete shaft (See Figure 5-9). At approximately 20.2
kips, concrete breakout failure cracks began to form on the concrete shaft while the torsional
cracks continued to widen (See Figure 5-10). At approximately 24.5 kips, the concrete breakout
failure cracks began to widen noticeably (See Figure 5-11). The foundation continued to be
loaded until the specimen stopped taking on additional load. The applied load peaked at
approximately 26.3 kips. At failure the foundation displayed the predicted breakout cone
indicated by bulging concrete deep within the foundation. As intended, the rest of the test
specimen did not fail before the predicted breakout failure occurred. Note that an applied load of
1 kip produces a flexural moment of 8 kip-ft and a torsional moment of 9 kip-ft.
The formation of the initial cracks was noteworthy because it indicated a change in the
concrete behavior from a concrete pedestal with anchor bolts and confining reinforcement. rather
than the 45 degree torsional cracks forming at the surface of the concrete closest to the base
plate, cracks parallel to the embedded pipe formed at the surface closest to the base plate. These
parallel cracks extended several inches down the foundation and then began to exhibit typical
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