Torsion Tests on Reinforced Concrete Slab Elements

Results of torsion tests to failure on nine orthogonally reinforced concrete slab elements are described and compared with various theoretical predictions. The specimens had dimensions of $200\mathrm{mm}\times 1\text{,}700\mathrm{mm}\times 1\text{,}700\mathrm{mm}(8\mathrm{in}\text{.}\times 67\mathrm{in}\text{.}\times 67\mathrm{in}\text{.})\text{.}$ Geometrical reinforcement ratios ranged from 0.25–1.0%. Post‐cracking behavior of the specimens, was accurately predicted by nonlinear analyses that take the softening of the concrete response in compression due to transverse tensile straining into account. Cracked linear response analyses provided very good approximations. Ultimate resistances were between 5–46% below yield‐line theory predictions. However, they were closely predicted by a lower‐bound limit analysis approach with an assumed effective concrete compressive strength equal to 45% of the measured uniaxial compressive strength. Observed peak moments exceeded ultimate resistance predictions based on the torsion design provisions of the current American building code requirements for reinforced concrete by 8%–117%. Except for one specimen that failed at a load 9% less than predicted, Canadian code predictions of the ultimate resistances were exceeded by 3–41%.