Flexural Crack Widths in Concrete Girders with High-Strength Reinforcement: Fid-Bau Portal

Flexural Crack Widths in Concrete Girders with High-Strength Reinforcement

Harries, Kent A. / Shahrooz, Bahram M. / Soltani, Amir

Abstract

The introduction of steel reinforcing bars having yield strengths exceeding 517 MPa (75 ksi) and often approaching 827 MPa (120 ksi) may allow for significant economies to be realized, particularly when used in conjunction with high-strength concrete. One implication of the adoption of higher-strength reinforcing steel is that reinforcing bar stresses (and therefore strains and consequently crack widths) at service load levels are expected to be greater than when conventional bars [having a yield of 414 MPa (60 ksi)] are used. A study of flexural crack widths of beams reinforced with high-strength ASTM A1035 reinforcing steel is presented. Discussion focuses on the behavior at loads corresponding to longitudinal reinforcing bar stresses of 248, 414, and 496 MPa (36, 60, and 72 ksi), representing service load levels (i.e., 0.6 $f_{y}$ ) for steel having $f_{y}$ = 414,690, and 827 MPa (60, 100, and 120 ksi), respectively. Average measured crack widths obtained from a series of flexural beams having reinforcing ratios ranging from 0.007 to 0.023 are found to be below the present AASHTO de facto limits for Class 1 and Class 2 exposure. The demonstrated conservativeness of existing ACI and AASHTO crack control provisions allows present specifications to be extended to the anticipated higher service level stresses associated with the use of high-strength reinforcing steel.