A constant ultimate concrete strain, regardless of axial load, can produce inaccurate strain representation in concrete sections. While this assumption minimally impacts section capacity, it contradicts basic mechanics, especially for sections under concentric axial load, where the ultimate resistance is reached when concrete strain is about 0.002. Based on specific design assumptions, more accurate values for the ultimate strain and stress-block parameters (alpha1, beta1) can be determined using the Stress-Block Parameters Tool for sections reinforced with steel or shape memory alloy bars. A proper understanding of these implications is essential for accurate use.
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Elbahy Y.I., Youssef M.A., Nehdi M., 2009, “Stress Block Parameters for Concrete Flexural Members Reinforced with Shape Memory Alloys”, Materials and Structures, 42(10): 1335-1351. The unique properties of superelastic Shape Memory Alloys (SMAs) have motivated researchers to explore their use as reinforcing bars. The capacity of a steel Reinforced Concrete (RC) section is calculated by assuming a maximum concrete strain εc-max and utilizing stress block parameters, α1 and β1, to simplify the nonlinear stress-strain curve of concrete. Recommended values for εcmax, α1, and β1 are given in different design standards. However, these values are expected to be different for SMA RC sections. In this paper, the suitability of using sectional analysis to evaluate the monotonic moment-curvature relationship for SMA RC sections is confirmed. A parametric study is then conducted to identify the characteristics of this relationship for steel and SMA RC sections. Specific mechanical properties are assumed for both steel and SMA. Results were used to judge on εc-max, α1, and β1 values given in the Canadian standard and to propose equations to estimate their recommended values for steel and SMA RC sections.
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