Shear Strength of Lightweight Concrete Bems wit Stirrups Near Code Minimum


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Title: Shear Strength of Lightweight Concrete Bems wit Stirrups Near Code Minimum

Author(s): J. A. Ramirez

Publication: Special Publication

Volume: 213


Appears on pages(s): 119-134

Keywords: beams (supports); crack control; ductility; high-strength concrete (HSC); lightweight-aggregate concrete; minimum shear reinforcement; shear strength; stirrups

Date: 5/22/2003

The new ACI 318-02 provision for minimum shear reinforcement, Equation (11-13), is based on tests of normal weight concrete beams. The evaluation of experimental data supported the code change making minimum shear reinforcement a function of the concrete cylinder strength. However, it also indicated that caution should be exercised when extrapolating current code minimums to beams with concrete cylinder strengths above 13 ksi (90 MPa). Because of the paucity of data on the shear strength of higher strength lightweight concrete beams with stirrups near code minimum values, the performance of this type of member is experimentally evaluated in this paper. The program consisted of four prestressed concrete beams, two specimens contained no stirrups, and two had stirrups near the code minimum. The specimens failed at shear capacities above calculated values. In the beams without stirrups, a 44% increase of the concrete cylinder strength resulted in a 28% increase of the measured shear strength. However, in the specimens with shear reinforcement (PC6S and PC10S), a 56% increase of the concrete cylinder strength only resulted in a 3% increase of the measured shear strength. The findings from the experimental program indicate that the current code minimum stirrups for lightweight concrete beams should he re-examined. The requirement results in a lower amount of minimum stirrups for higher strength lightweight concretes in comparison to the minimum amount required for an otherwise identical normal-weight concrete beam.