Flexural Strength and Ductility of High-Strength Concrete Columns

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Title: Flexural Strength and Ductility of High-Strength Concrete Columns

Author(s): R. Park, H. Tanaka and B. Li

Publication: Special Publication

Volume: 176

Issue:

Appears on pages(s): 237-258

Keywords: Columns (supports); confinement; ductility; earthquake-resistant structures; flexural strength; high-strength concrete; reinforced concrete

Date: 10/1/1998

Abstract:
High strength concrete with a specified compressive cylinder strength fi of up to 70 MPa for ductile elements in seismic design and of up to 100 MPa for other elements is now permitted by the recently revised New Zealand concrete design standard NZS 3101:1995. Also, longitudinal reinforcement with a characteristic yield strength of up to 500 MPa is allowed, and for transverse reinforcement in strength calculations a useable steel stress of up to 500 MPa for shear strength and 800 MPa for confinement is permitted. For concrete with f' f' c greater than 55 MPa the parameters for the equivalent rectangular compressive stress block have been modified to take into account the stress-strain characteristics of high strength concrete. Also, new design equations for confining reinforcement have been included to better account for the affect of the variation of axial load level. Simulated seismic load tests have been conducted in New Zealand to investigate the behaviour of high strength concrete columns confined with normal and very high strength transverse reinforcement. The tests demonstrated that the yield strength of very high strength confining reinforcement may not be attained at the stage when the column reaches the peak flexural strength and that the thickness of concrete cover has an important influence on the behaviour of the columns.