Making sense of minimum flexural reinforcement requirements for reinforced concrete members

摘要

>Minimum flexural reinforcement requirements have been a source of controversy for many years. The purpose of such provisions is to encourage ductile behavior in flexural members by providing a reasonable margin of safety between first cracking and flexural failure or, alternatively, a reasonable amount of overstrength beyond the applied factored loads. The primary objectives of this study were to summarize the apparent origin of current minimum reinforcement provisions, examine the margin of safety provided by existing provisions for reinforced concrete members of different sizes and shapes, and propose new requirements when they provide more-consistent results than those from existing provisions. Five existing or proposed methods were included in the study. Parametric analyses show that the proposed method provides the most reasonable margins of safety among the methods examined. The study focuses on determinate reinforced concrete beams, which include only mild tensile reinforcement and no prestressing. High-strength steel and concrete were included. The study also found that, in many cases, flexural failure at minimum reinforcement levels can be initiated by crushing of the concrete rather than the fracture of the reinforcing steel.>References>1. American Association of State Highway and Transportation Officials (AASHTO). 2007. AASHTO LRFD Bridge Design Specifications. 4th ed. Washington, DC: AASHTO. >2. American Concrete Institute (ACI) Committee 318. 2008. Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary (ACI 318R-08). Farmington Hills, MI: ACI. >3. Freyermuth, C. L., and B. O. Aalami. 1997.target="_blank" title=" Unified Minimum Flexural Reinforcement Requirements for Reinforced and Prestressed Concrete Members." href=" http://dx.doi.org/10.14359/492 "> Unified Minimum Flexural Reinforcement Requirements for Reinforced and Prestressed Concrete Members. ACI Structural Journal, V. 94, No. 4 (July- August): pp. 409-420. >4. American Segmental Bridge Institute (ASBI). 2007. ASBI Proposed Specification Revision WAI 106B, Minimum Flexural Reinforcement. Unpublished proposal prepared for AASHTO Technical  Subcommittee T-10. >5. Seiss, C. P. 1992. Minimum Reinforcement Requirements for Flexural Members in ACI 318 - Reinforced and Prestressed Concrete. Unpublished paper prepared for ACI Committee 318, Farmington  Hills, MI. >6. Wang, C., and C. G. Salmon. 2002. Reinforced Concrete Design. 6th ed. pp. 558-560. Hoboken, NJ: John Wiley and Sons Inc. >7. ACI Committee 318. 1995. target="_blank" title="Building Code Requirements for Structural Concrete (ACI 318-95) and Commentary (ACI 318R-95" href="http://dx.doi.org/10.1061/(asce)1076-0431(1996)2:3(120.3) ">Building Code Requirements for Structural Concrete (ACI 318-95) and Commentary (ACI 318R-95). Detroit, MI: ACI. >8. CEB-FIP. 1990. target="_blank" title="CEB-FIP Model Code for  Concrete Structures" href="http://dx.doi.org/10.1680/ceb-fipmc1990.35430 ">CEB-FIP Model Code for  Concrete Structures. 4th ed. London, England: Thomas Telford Ltd. >9. ASTM Internationaltarget="_blank" title=" A615, 2007" href="http://dx.doi.org/10.1520/a0615_a0615m-14 "> A615, 2007. Standard Specification for Deformed and Plain Carbon Steel Bars for Concrete Reinforcement. West Conshohocken, PA: ASTM International. >10. Leonhardt, F. 1964. Prestressed Concrete Design and Construction. 2nd ed. [In German.] Translated by C. Armerongen. Berlin-Munich, Germany: Wilhelm, Ernst & Sohn. >11. Collins, M. P., and D. Mitchell. 1991. Prestressed Concrete Structures, pp. 61-65. Englewood Cliffs, NJ: Prentice-Hall Inc. >12. ASTM International target="_blank" title="A706. 2006" href="http://dx.doi.org/10.1520/a0706_a0706m-06 ">A706. 2006. Standard Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement. West Conshohocke