Deformation Capacity and Strength of RC Frame Members with High-Strength Materials

Synopsis: Some implications of using high-strength concrete and steel materials in reinforced concrete frame members are discussed in terms of both flexural design and behavior. Through an example, it is demonstrated that the computed sectional curvature is highly sensitive to the choice of rectangular stress block used to model compression zone stresses of high-strength concrete. Comparison of various models suggests that the use of the stress block model defined in the ACI Building Code tends to overestimate curvature for concrete strengths exceeding 12 ksi (83 MPa). In addition, recent test data are presented for flexure-dominated concrete members reinforced with high-strength steel bars. The effects of replacing Grade 60 (410) flexural reinforcement with Grade 100 (690) steel on deformation capacity, stiffness, and strength are examined. Test data support the viability of using Grade 100 (690) longitudinal reinforcement to resist loads that induce force-displacement response well into the nonlinear range.