Alternative Support Systems for Cantilever - National Transportation ...

4.4 Concrete Block and Tie-Down Design
For both tests, the concrete block was designed to provide a fixed base for the concrete
shaft. The design of the reinforcement was based upon a strut-and-tie model design outlined in
ACI 318-08 Appendix A (5). The reinforcement was also analyzed using the beam theory to be
sure that the reinforcement was adequate in shear and flexure. The information obtained from
these approaches determined that 6 #8 bars, each with a 12 in. hook on each end, would be
sufficient. 3 of the #8 bars would be placed on the top of the block and the remaining 3 #8 bars
would be placed on the bottom of the block. Additional reinforcement included two cages of #4
bars placed in the block’s front and back faces. These additional reinforcement cages would meet
the supplementary reinforcement requirements. Using this reinforcement arrangement, the
concrete block was determined to be a fixed base for the concrete shaft.
The tie-down was designed to be comprised of two channels connected by welded plates.
The channels individually and as a channel assembly were designed for flexure and local
buckling as specified in AISC 2005 (15). Each channel assembly’s resistance was required to not
exceed the floor capacity of 100 kips on either end, or 200 kips total. The bearing capacity of the
concrete at the point of contact between the channel assembly and the concrete block was also
checked to ensure that the loading from the channel would not cause the concrete to fail in that
region.
4.5 Instrumentation
To successfully obtain data from the experimental program, a plan for instrumentation
needed to be designed. The rotational stiffness of the concrete shaft was necessary to understand
the behavior of the newly designed concrete shaft. To obtain this information, a system of linear
variable displacement transducers (LVDTs) would need to be arranged.
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