Title:
Rectangular Stress Block for Nonrectangular Compression Zone
Author(s):
Lawrence F. Khan and Karl F. Meyer
Publication:
Structural Journal
Volume:
92
Issue:
3
Appears on pages(s):
304-310
Keywords:
flexural strength; high-strength concrete; modulus of elasticity; strains; stress block; Structural Research
DOI:
10.14359/1131
Date:
5/1/1995
Abstract:
Tests of nineteen beams made with high-strength concrete showed that use of the current ACI rectangular stress block on both triangular and circular compression zones provided conservative results. Concrete strengths were 9630, 12,800, and 14,830 psi (66.4, 88.2, and 102.2 MPa). Eight beams were constructed with a semicircular cross section to model the compression zone found in a circular column under combined axial load and bending, while eleven were constructed with a triangular cross section to model rectangular columns under biaxial bending. The amount of reinforcing was varied to influence the size of the compression zone and location of neutral axis. Each beam was gaged to measure strain in both the concrete and steel. The rectangular stress block may be used to predict the moment strength of sections with nonrectangular compression zones made with high-strength concrete, although it is slightly unconservative for triangular compression zones.