Document Type : Research Paper
Authors
Civil Engineering Department, University of Technology, Baghdad, Iraq
Abstract
The requirements of minimum flexural reinforcement in the last decades have been a reason for controversy. The structural behavior of beams in bending is the best way of investigating and evaluating the minimum reinforcement in flexure. For this purpose, twelve singly reinforced concrete beams with a rectangular cross-section of (125 mm) width by (250 mm) height and (1800 mm) length were cast and tested under two-point loads up to failure. These beams were divided into three groups with different compressive strengths (25, 50, and 80 MPa). Each group consists of four beams with different amounts of tension steel reinforcement approximately equal to (0% Asmin, 50% Asmin, 100% Asmin and 150% Asmin), two bar diameters (Ø6 mm and Ø8 mm) were used as the longitudinal tension reinforcement with different yield and ultimate strengths, the minimum amount of reinforcement required is calculated based on ACI 318M-2014 code. The results show that for the reinforced concrete beams, the flexural reinforcement in NSC beams increases the first cracking load and the increment increased with an increasing amount of reinforcement, while for HSC beams the increasing in first cracking load are very little when the quantity of reinforcement less than the minimum flexural reinforcement and increased with the increasing amount above the minimum flexural reinforcement. The equation of ACI 318M-14 code gives adequate minimum flexural reinforcement for NSC and overestimate value for HSC up to (83 MPa), A new formula is proposed for HSC rectangular beams up to (90 MPa) concrete compressive strength by reducing the equation of ACI 318M-14 code for minimum flexural reinforcement by a factor depending on concrete compressive strength.
Keywords
[2] C. Bosco, A. Carpinteri, and P. G. Debernardi, “Minimum reinforcement in high-strength concrete,” Journal of Structural Eng., ASCE, V. 116, No. 2, pp. 427-437, 1990.
[3] ACI Committee 318, “Building code requirements for reinforced concrete (ACI 318M-14) and commentary (ACI 318RM-14),” American Concrete Institute, Farmington Hills, Michigan,519pp, 2014.
[4] W. L. Gamble, “A minimum flexural reinforcement puzzle current requirements need to be updated for modern material strengths,” Concrete International Magazine, pp. 47-49, January, 2017.
[5] R. Park, “Ductility evaluation from laboratory and analytical testing,” Proceedings of the 9th World Conference on Earthquake Engineering, Vol. VIII, Tokyo–Kyoto, pp. 605–616, 1988.
[6] H. J. Pam, J. C. M. Ho, and A. K. H. Kwan, “Minimum flexural ductility design of high strength concrete beams,” Magazine of Concrete Research, V. 56, No. 1, pp. 13–22, 2004.
[7] T. M. Elrakib, “Performance evaluation of HSC beams with low flexural reinforcement,” Housing and Building National Research Center HBRC Journal, V.9, pp. 49-59, 2013.
[9] C.L. Freyermuth, and B. O. Aalami, “Unified minimum flexural reinforcement requirements for reinforced and prestressed concrete members,” ACI Structural Journal, V. 94, No. 4, pp. 409-420, 1997.
[10] ACI Committee 363, “Report on high-strength concrete (ACI 363R-10),” American Concrete Institute, Farmington Hills, Michigan, 2010.
[11] F.F. Wafa, and S. A. Ashour, “Minimum flexural reinforcements of high strength concrete beams,” ACI Special Publication SP 172-30, pp. 549-571, 1999.
[12] S. J. Seguirant, R. B. Brice, and B. Khaleghi, “Making sense of minimum flexural reinforcement requirements for reinforced concrete members,” PCI Journal, V. 55, No. 3, pp. 64-85, 2010.
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