Title:
Under-Reinforced Concrete: A Realistic Examination of Strain Compatibility Concrete in Flexure
Author(s):
Robert W. Cannon
Publication:
Structural Journal
Volume:
91
Issue:
2
Appears on pages(s):
221-228
Keywords:
anchorage; compressive strength; cracking (fracturing); ductility; flexural strength; modulus of elasticity; shrinkage; Structural Research
DOI:
10.14359/4598
Date:
3/1/1994
Abstract:
The development of the ultimate strength approach to design of reinforced concrete and its test basis is reviewed and discussed. Code requirements for compatibility of stress and strain are limited principally to balanced strain conditions at failure, and most designers associate code design capacity with structural failure. This paper examines the compatibility of stress and strain, throughout the depth of the compressive stress block, to relate maximum strains at the surface of the concrete and steel strains at failure with design capacity, and evaluates structural performance with respect to the degree of under-reinforcement. Design capacity in flexure is not synonymous with structural failure of rectangular concrete members, as normally assumed, particularly with steel ratios less than 1/4 of balanced steel requirements. Recommendations are made for increasing design shear allowables dependent on the degree of under-reinforcement for reducing usable strain limits for high-strength concrete, for lowering maximum steel ratios for combined bending and axial loads without compressive reinforcement, and for designing moment connections for multiple anchors in concrete.