Flexural Strength and Ductility Improvement of NSC beams
In order to calculate the flexural strength of
normal-strength concrete (NSC) beams, the nonlinear actual concrete
stress distribution within the compression zone is normally replaced
by an equivalent rectangular stress block, with two coefficients of α
and β to regulate the intensity and depth of the equivalent stress
respectively. For NSC beams design, α and β are usually assumed
constant as 0.85 and 0.80 in reinforced concrete (RC) codes. From an
earlier investigation of the authors, α is not a constant but significantly
affected by flexural strain gradient, and increases with the increasing
of strain gradient till a maximum value. It indicates that larger
concrete stress can be developed in flexure than that stipulated by
design codes. As an extension and application of the authors- previous
study, the modified equivalent concrete stress block is used here to
produce a series of design charts showing the maximum design limits
of flexural strength and ductility of singly- and doubly- NSC beams,
through which both strength and ductility design limits are improved
by taking into account strain gradient effect.
[1] ACI Committee 318, Building Code Requirements for Reinforced
Concrete and Commentary ACI 318M-08, Manual of Concrete Practice,
American Concrete Institute, Michigan, USA, 465pp, 2008.
[2] A.H. Mattock, L.B. Kriz, and E. Hognestad , "Rectangular concrete stress
distribution in ultimate strength design", ACI Journal, vol. 57, no. 1,
pp.875-928, 1961.
[3] E. Hognestad, N.W. Hanson, and D. McHenry, "Concrete stress
distribution in ultimate strength design", ACI Journal, vol. 52, no. 12,
pp.455-480, 1955.
[4] European Committee for Standardization (ECS), Eurocode 2: Design of
Concrete Structures: Part 1-1: General Rules and Rules for Buildings,
British Standard Institution, London, UK, 225pp, 2004.
[5] G. Fathifazl, A.G. Razaqpur, O.B. Isgor, A. Abbas, B. Fournier and S.
Foo, "Shear strength of reinforced recycled concrete beams without
stirrups", Magazine of Concrete Research, vol. 61, no. 7, pp.477-490,
2009.
[6] H. J. Pam, A. K. H. Kwan, and J. C. M. Ho, "Post-peak behavior and
flexural ductility of doubly reinforced normal- and high-strength concrete
beams," Structural Engineering and Mechanics, vol. 12, no. 5,
pp.459-474, 2001.
[7] H. J. Pam, A. K. H. Kwan, and M. S. Islam, "Flexural strength and
ductility of reinforced normal- and high-strength concrete beams,"
Structures and Buildings, vol. 146, no. 4, pp.381-389, 2001.
[8] H.H.H. Ibrahim and J.G. MacGregor, "Flexural behavior of laterally
reinforced high-strength concrete sections", ACI Structural Journal, vol.
93, no. 6, pp.674-684, 1996.
[9] H.H.H. Ibrahim and J.G. MacGregor, "Modification of the ACI
rectangular stress block for high-strength concrete", ACI Structural
Journal, vol. 94, no.1, pp.40-48, 1997.
[10] J. C. M. Ho and J. Peng, "Strain gradient effects on flexural strength
design of normal-strength concrete beams," The Structural Design of Tall
and Special Buildings, doi: 10.1002/tal.655, 2010.
[11] J. C. M. Ho and J. Peng, "Strain gradient effects on flexural strength
design of normal-strength concrete columns," Engineering Structures,
vol. 33, no. 1, pp.18-31, 2011.
[12] M. Pecce and G. Fabbrocino, "Plastic rotation capacity of beams in
normal and high-performance concrete", ACI Structural Journal, vol. 96,
no. 2, pp.290-296, 1999.
[13] P.G. Debernardi and M. Taliano, "On evaluation of rotation capacity for
reinforced concrete beams", ACI Structural Journal, vol. 99, no. 3,
pp.360-368, 2002.
[14] S.A. Ashour, "Effect of compressive strength and tensile reinforcement
ratio on flexural behaviour of high-strength concrete beams",
Engineering Structures, vol. 25, no. 8, pp.1083-1096, 2000.
[15] S.S.E. Lam, B. Wu, Z.Q. Liu and Y.L. Wong, "Experimental study on
seismic performance of coupling beams not designed for ductility",
Structural Engineering and Mechanics, vol. 28, no. 3, pp.317-333, 2008.
[16] Standards New Zealand, NZS 3101, Concrete Structures Standard, Part
1 - The Design of Concrete Structures, Concrete Standard New Zealand,
Wellington, New Zealand, 2006.
[17] T.H. Tan and N.B. Nguyen, "Determination of stress-strain curves of
concrete from flexure tests", Magazine of Concrete Research, vol. 56, no.
4, pp.243-250, 2004.
[18] T.H. Tan and N.B. Nguyen, "Flexural behavior of confined high-strength
concrete columns", ACI Structural Journal, vol. 102, no. 2, pp.198-205,
2005.
[19] T. Ozbakkaloglu and M. Saatcioglu, "Rectangular stress block for
high-strength concrete", ACI Structural Journal, vol. 101, no. 4,
pp.475-483, 2004.
[1] ACI Committee 318, Building Code Requirements for Reinforced
Concrete and Commentary ACI 318M-08, Manual of Concrete Practice,
American Concrete Institute, Michigan, USA, 465pp, 2008.
[2] A.H. Mattock, L.B. Kriz, and E. Hognestad , "Rectangular concrete stress
distribution in ultimate strength design", ACI Journal, vol. 57, no. 1,
pp.875-928, 1961.
[3] E. Hognestad, N.W. Hanson, and D. McHenry, "Concrete stress
distribution in ultimate strength design", ACI Journal, vol. 52, no. 12,
pp.455-480, 1955.
[4] European Committee for Standardization (ECS), Eurocode 2: Design of
Concrete Structures: Part 1-1: General Rules and Rules for Buildings,
British Standard Institution, London, UK, 225pp, 2004.
[5] G. Fathifazl, A.G. Razaqpur, O.B. Isgor, A. Abbas, B. Fournier and S.
Foo, "Shear strength of reinforced recycled concrete beams without
stirrups", Magazine of Concrete Research, vol. 61, no. 7, pp.477-490,
2009.
[6] H. J. Pam, A. K. H. Kwan, and J. C. M. Ho, "Post-peak behavior and
flexural ductility of doubly reinforced normal- and high-strength concrete
beams," Structural Engineering and Mechanics, vol. 12, no. 5,
pp.459-474, 2001.
[7] H. J. Pam, A. K. H. Kwan, and M. S. Islam, "Flexural strength and
ductility of reinforced normal- and high-strength concrete beams,"
Structures and Buildings, vol. 146, no. 4, pp.381-389, 2001.
[8] H.H.H. Ibrahim and J.G. MacGregor, "Flexural behavior of laterally
reinforced high-strength concrete sections", ACI Structural Journal, vol.
93, no. 6, pp.674-684, 1996.
[9] H.H.H. Ibrahim and J.G. MacGregor, "Modification of the ACI
rectangular stress block for high-strength concrete", ACI Structural
Journal, vol. 94, no.1, pp.40-48, 1997.
[10] J. C. M. Ho and J. Peng, "Strain gradient effects on flexural strength
design of normal-strength concrete beams," The Structural Design of Tall
and Special Buildings, doi: 10.1002/tal.655, 2010.
[11] J. C. M. Ho and J. Peng, "Strain gradient effects on flexural strength
design of normal-strength concrete columns," Engineering Structures,
vol. 33, no. 1, pp.18-31, 2011.
[12] M. Pecce and G. Fabbrocino, "Plastic rotation capacity of beams in
normal and high-performance concrete", ACI Structural Journal, vol. 96,
no. 2, pp.290-296, 1999.
[13] P.G. Debernardi and M. Taliano, "On evaluation of rotation capacity for
reinforced concrete beams", ACI Structural Journal, vol. 99, no. 3,
pp.360-368, 2002.
[14] S.A. Ashour, "Effect of compressive strength and tensile reinforcement
ratio on flexural behaviour of high-strength concrete beams",
Engineering Structures, vol. 25, no. 8, pp.1083-1096, 2000.
[15] S.S.E. Lam, B. Wu, Z.Q. Liu and Y.L. Wong, "Experimental study on
seismic performance of coupling beams not designed for ductility",
Structural Engineering and Mechanics, vol. 28, no. 3, pp.317-333, 2008.
[16] Standards New Zealand, NZS 3101, Concrete Structures Standard, Part
1 - The Design of Concrete Structures, Concrete Standard New Zealand,
Wellington, New Zealand, 2006.
[17] T.H. Tan and N.B. Nguyen, "Determination of stress-strain curves of
concrete from flexure tests", Magazine of Concrete Research, vol. 56, no.
4, pp.243-250, 2004.
[18] T.H. Tan and N.B. Nguyen, "Flexural behavior of confined high-strength
concrete columns", ACI Structural Journal, vol. 102, no. 2, pp.198-205,
2005.
[19] T. Ozbakkaloglu and M. Saatcioglu, "Rectangular stress block for
high-strength concrete", ACI Structural Journal, vol. 101, no. 4,
pp.475-483, 2004.
@article{"International Journal of Architectural, Civil and Construction Sciences:52058", author = "Jun Peng and Johnny Ching Ming Ho", title = "Flexural Strength and Ductility Improvement of NSC beams", abstract = "In order to calculate the flexural strength of
normal-strength concrete (NSC) beams, the nonlinear actual concrete
stress distribution within the compression zone is normally replaced
by an equivalent rectangular stress block, with two coefficients of α
and β to regulate the intensity and depth of the equivalent stress
respectively. For NSC beams design, α and β are usually assumed
constant as 0.85 and 0.80 in reinforced concrete (RC) codes. From an
earlier investigation of the authors, α is not a constant but significantly
affected by flexural strain gradient, and increases with the increasing
of strain gradient till a maximum value. It indicates that larger
concrete stress can be developed in flexure than that stipulated by
design codes. As an extension and application of the authors- previous
study, the modified equivalent concrete stress block is used here to
produce a series of design charts showing the maximum design limits
of flexural strength and ductility of singly- and doubly- NSC beams,
through which both strength and ductility design limits are improved
by taking into account strain gradient effect.", keywords = "Concrete beam, Ductility, Equivalent concrete stress,Normal strength, Strain gradient, Strength", volume = "5", number = "11", pages = "535-7", }
