Alternative Support Systems for Cantilever - National Transportation ...

4.6 Summary of Torsion Design
To summarize, the previous sections describe the design of the various components of both
experimental programs. For the torsion test, the key element of the design that dictated the rest of
the design was the concrete shaft. The concrete breakout or bearing strength of the shaft with the
embedded pipe and plate apparatus was the ultimate strength of the entire system. All other
components of the system were designed to preclude failure from these elements. This way the
experimental strength of the embedded pipe and plate system could be observed and appropriate
design guidelines could be written to detail the strength of the new system. Appendix A shows
detailed and dimensioned drawings of the testing apparatus. Appendix B shows detailed
calculations for the test apparatus.
The most critical components of the design were the embedded pipe and plate apparatus
and the reinforced concrete shaft. As long as the components of the concrete shaft and embedded
pipe and plate section exceeded that of the equivalent torsional concrete breakout strength then
the design was sufficient.Table 4-1, shown below, summarizes the essential design components,
their equivalent torsional strengths, whether the strengths are mean or nominal, and their ratio
compared to the concrete breakout strength.
Table 4-1. Summary of pertinent design strengths for torsion test with 5500 psi concrete
Failure Mode Capacity
58
Mean or
Nominal?
Predicted
Load
Ratio of Failure
Capacities
Embedded Pipe and Stiffeners
Equivalent Torsion from Shear
Parallel to an Edge 249 kip-ft Mean 27.67 1.00
Equivalent Torsion from Side Face
Blowout 391 kip-ft Mean 43.44 1.57
Circular Shaft - 26"
Torsion 373 kip-ft Nominal 41.44 1.50
Flexure 252 kip-ft Nominal 126.00 2.02
"Superstructure" Pipes - 16" x .5"
Torsion 359 kip-ft Nominal 39.89 1.44
Flexure 392 kip-ft Nominal 196.00 3.14