> For the complete documentation index, see [llms.txt](https://docs.enercalc.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.enercalc.com/sel-faq/using-the-software/calculation-modules/beams2/concrete-beams/deflection-calculation-methods.md). # Deflection Calculation Methods Why the Deflection Calculation Method option was removed from the Concrete Beam module and how it affects existing calculations. ## What happened to the option to specify the "Deflection Calculation Method"? As of Build 20.25.01.16, the user-specified option for the "Deflection Calculation Method" in the Concrete Beam module has been removed. This change was made to ensure compliance with ACI 318 standards and to eliminate potential errors that could arise from users selecting methods not supported under their chosen ACI governing code. The deflection method is now automatically aligned with the governing code selected in the module to ensure that all calculations adhere strictly to the corresponding ACI 318 requirements. ## What does this mean for my existing concrete beam calculations? For projects created in versions prior to Build 20.25.01.16, you may notice some adjustments in the calculated effective moment of inertia, Ie, due to the standardized deflection calculation methods now employed. Specifically: **For governing codes adopting ACI 318-14:** The module calculates Ie using Branson's formula as outlined in ACI 318-14 Equation 24.2.3.5(a), but with powers of 4 instead of 3. The "fourth-power" version of Branson's formula, as recommended by ACI 435R-20, provides a more accurate representation of stiffness variations along the member for section-based analyses. In contrast, the "third-power" version in Equation 24.2.3.5(a) represents an averaged Ie over the full member length, which is not suitable for the section-based analysis performed by the Concrete Beam module. | **Original User-Specified Deflection Calculation Method** | **I\*\*\*\*e** **formula prior to** **Build 20.25.01.16** | **I\*\*\*\*e** **formula for** **Build 20.25.01.16 and later** | **Net Result** | | --------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------- | -------------- | | **Ieff using Bischoff Method** | I\_{e}= \left( \frac{M\_{cr}}{M\_{a}} \right)^{4}I\_{g} + \left\\\[1- \left( \frac{M\_{cr}}{M\_{a}} \right)^{4} \right\\]I\_{cr} | I\_{e}= \left( \frac{M\_{cr}}{M\_{a}} \right)^{4}I\_{g} + \left\\\[1- \left( \frac{M\_{cr}}{M\_{a}} \right)^{4} \right\\]I\_{cr} | **No change** | | **Ieff per ACI 318-14 24.2.3.5(a)** | I\_{e}= \left( \frac{M\_{cr}}{M\_{a}} \right)^{3}I\_{g} + \left\\\[1- \left( \frac{M\_{cr}}{M\_{a}} \right)^{3} \right\\]I\_{cr} | **Minor increase in deflections** | | **For governing codes adopting ACI 318-19:** The effective moment of inertia, Ie, is calculated based on the provisions in ACI 318-19. | **Original User-Specified Deflection Calculation Method** | **I\*\*\*\*e** **formula prior to** **Build 20.25.01.16** | **I\*\*\*\*e** **formula for** **Build 20.25.01.16 and later** | **Net Result** | | --------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------- | | **Ieff using Bischoff Method** | I\_{e}= \left( \frac{M\_{cr}}{M\_{a}} \right)^{4}I\_{g} + \left\\\[1- \left( \frac{M\_{cr}}{M\_{a}} \right)^{4} \right\\]I\_{cr} | | **Potential for moderate increase in deflections, particularly for shallow members or those with low reinforcement ratios** | | **Ieff per ACI 318-19** **Table 24.2.3.5** | | **No change** | | These changes ensure that all deflection calculations are compliant with the selected ACI code and remove any risk of non-code-compliant designs resulting from unsupported deflection methods. --- # Agent Instructions This documentation is published with GitBook. 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