Title:
Computing Deflections Using ACI CODE-318-19 and Beyond, Part 2
Author(s):
Peter H. Bischoff
Publication:
Concrete International
Volume:
47
Issue:
3
Appears on pages(s):
51-54
Keywords:
moment, member, cracking, stress
DOI:
10.14359/51745652
Date:
3/1/2025
Abstract:
This is the second article in a five-part series on calculating deflections for members not meeting minimum thickness requirements in accordance with ACI CODE-318-19. It reviews the development of a new expression for the effective moment of inertia Ie used to calculate immediate deflection of cracked reinforced (nonprestressed) concrete flexural members at service load and justifies the need for a change.
Related References:
1. ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19),” American Concrete Institute, Farmington Hills, MI, 2019, 624 pp.
2. Bischoff, P.H., “Computing Deflections Using ACI CODE-318-19 and Beyond, Part 1,” Concrete International, V. 47, No. 2, Feb. 2025, pp. 47-50.
3. Branson, D.E., “Instantaneous and Time-Dependent Deflections of Simple and Continuous Reinforced Concrete Beams,” HPR Report No. 7, Part I, Alabama Highway Department, Bureau of Public Roads, Montgomery, AL, 1965, 78 pp.
4. ACI Committee 318, “Building Code Requirements for Reinforced Concrete (ACI 318-71),” American Concrete Institute, Farmington Hills, MI, 1971, 78 pp.
5. ACI Committee 318, “Building Code Requirements for Reinforced Concrete (ACI 318-63),” American Concrete Institute, Farmington Hills, MI, 1963, 144 pp.
6. Bischoff, P.H., “Reevaluation of Deflection Prediction for Concrete Beams Reinforced with Steel and Fiber Reinforced Polymer Bars,” Journal of Structural Engineering, V. 131, No. 5, May 2005, pp. 752-767.
7. Bischoff, P.H., “Comparison of Existing Approaches for Computing Deflection of Reinforced Concrete,” ACI Structural Journal, V. 117, No. 1, Jan. 2020, pp. 231-240.
8. Rao, P.S., and Subrahmanyam, B.V., “Trisegmental Moment-Curvature Relations for Reinforced Concrete Members,” ACI Journal Proceedings, V. 70, No. 5, May 1973, pp. 346-351.
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11. Gilbert, R.I., “Deflection Calculation for Reinforced Concrete Structures—Why We Sometimes Get It Wrong,” ACI Structural Journal, V. 96, No. 6, Nov.-Dec. 1999, pp. 1027-1032.
12. Stivaros, P.C., “Control of Deflection in Concrete Slabs and Effects of Construction Loads,” Andy Scanlon Symposium on Serviceability and Safety of Concrete Structures: From Research to Practice, SP-284, P.H. Bischoff, E. Musselman, S. Gross, and H. Nassif, eds., American Concrete Institute, Farmington Hills, MI, 2012, pp. 17-1-17-22.
13. Gilbert, R.I., “Discussion of ‘Reevaluation of Deflection Prediction for Concrete Beams Reinforced with Steel and Fiber Reinforced Polymer Bars’ by Peter H. Bischoff,” Journal of Structural Engineering, V. 132, No. 8, Aug. 2006, pp. 1328-1330.
14. Bischoff, P.H., and Torres, L., “Rational Approach for Computing Long-Term Deflection of Reinforced Concrete,” ACI Structural Journal, V. 118, No. 2, Mar. 2021, pp. 215-224.
15. ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14),” American Concrete Institute, Farmington Hills, MI, 2014, 519 pp.
16. Bischoff, P.H., and Scanlon, A., “Effective Moment of Inertia for Calculating Deflections of Concrete Members Containing Steel Reinforcement and Fiber-Reinforced Polymer Reinforcement,” ACI Structural Journal, V. 104, No. 1, Jan.-Feb. 2007, pp. 68-75.
17. Bischoff, P.H., “Service Load Deflection of Tilt-Up Concrete Wall Panels,” Canadian Journal of Civil Engineering, V. 45, No. 8, Aug. 2018, pp. 684-689.
18. ACI Committee 440, “Building Code Requirements for Structural Concrete Reinforced with Glass Fiber-Reinforced Polymer (GFRP) Bars—Code and Commentary (ACI CODE-440.11-22),” American Concrete Institute, Farmington Hills, MI, 2022, 255 pp.
19. CSA A23.3:24, “Design of Concrete Structures,” CSA Group, Toronto, ON, Canada, 2024, 335 pp.
20. AASHTO “LRFD Bridge Design Specifications,” 10th edition, American Association of State Highway and Transportation Officials, Washington, DC, 2024.
21. CSA S6:25, “Canadian Highway Bridge Design Code,” CSA Group, Toronto, ON, Canada. (in-press–scheduled for publication in July, 2025).