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Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete.
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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Examination of Stress Block Parameters for High-Strength Concrete in the Context of ACI 318 Code
Author(s): Sungjin Bae and Oguzhan Bayrak
Publication: Special Publication
Appears on pages(s): 1-20
Keywords: high strength concrete; stress block; interaction curve; column; beam.
Abstract:In an attempt to provide consistently conservative yet reliable estimations of flexural and axial strengths of concrete columns, various stress block parameters have been proposed within the last two decades. The fact that flexural and axial strengths of many tested high-strength concrete columns were overpredicted by the current ACI 318 stress block parameters is the primary motivation behind all of the proposals for stress block parameters.
Chapter 10 (Flexure and axial loads) of ACI 318-11 introduces the concrete stress block parameters and provides design formulas for calculating flexural and axial strengths and bearing strengths. The stress block is also used for various design applications in other chapters of ACI 318. Those chapters include Chapter 18 (Prestressed concrete), Chapter 22 (Structural plain concrete), Appendix A (Strut-and-tie models) and Appendix B (Alternative provisions for reinforced and prestressed concrete flexural and compression members). All ACI 318 design implications stemming from any suggested changes for the concrete stress block parameters needs to be examined holistically.
This paper provides a comprehensive examination of various stress block parameters. Flexural and axial strengths predicted by different stress blocks are compared with experimentally-obtained strengths from 224 column tests. Normalized P-M interaction curves are developed for this purpose. In addition, the impact of change of stress block parameters on other design expressions is examined. They include the bonded tendon stress in prestressed concrete and the compressive stress of bottle-shaped struts in strut-and-tie model.
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