Maximum Crack Width in Reinforced Concrete Flexural Members

THE MAXIMUM CRACK WIDTH MEASUREMENTS FROM A NUMBER OF CRACK WIDTH INVESTIGATIONS WERE EXAMINED USING STATISTICAL METHODS. PREVIOUSLY PROPOSED EQUATIONS FOR MAXIMUM CRACK WIDTH WERE COMPARED AND NEW EQUATIONS WERE PROPOSED AS A RESULT OF THE ANALYSES. INTEREST IN CRACK WIDTHS IN FLEXURAL MEMBERS HAS BEEN STIMULATED BY THE TREND TO USE HIGH STRENGTH DEFORMED REINFORCING BARS. VARIOUS INVESTIGATIONS HAVE PRODUCED MUCH INFORMATION ABOUT THE WIDTH AND SPACING OF CRACKS. HOWEVER, DUE TO THE RELATIVELY LARGE SCATTER IN THE WIDTH OF THE LARGEST CRACKS, AND TO THE LARGE NUMBER OF INTERRELATED VARIABLES PRESENT IN REINFORCED CONCRETE BEAMS, AGREEMENT WAS LACKING AMONG THE INVESTIGATORS AS TO THE MOST PERTINENT VARIABLES INFLUENCING THE SIZE OF THE CRACKS. BY USING DATA FROM SIX DIFFERENT INVESTIGATIONS, THE SAMPLE WAS LARGE AND DIVERSE ENOUGH TO PERMIT RELIABLE STATISTICAL ANALYSES. THE MAXIMUM CRACK WIDTH MEASURED ON A BEAM AT A CERTAIN STEEL STRESS LEVEL REPRESENTED A STATISTICAL SAMPLE. IN THE COMPUTER INPUT, EACH SAMPLE WAS ACCOMPANIED BY ALL BEAM DETAILS THAT COULD INFLUENCE THE CRACK WIDTH. THE MAXIMUM CRACK WIDTH ON THE TENSION FACE OF THE BEAM AND THE MAXIMUM CRACK WIDTH ON THE SIDE OF THE BEAM AT THE LEVEL OF THE TENSILE REINFORCEMENT WERE ANALYZED SEPARATELY. THE FOLLOWING MAJOR CONCLUSIONS RESULTED FROM THE ANALYSIS OF THE MAXIMUM CRACK WIDTH: (1) THE STEEL STRESS IS THE MOST IMPORTANT VARIABLE, (2) THE DIAMETER OF THE REINFORCING BAR IS NOT A MAJOR VARIABLE, (3) THE THICKNESS OF THE CONCRETE COVER IS IMPORTANT, BUT IT IS NOT THE ONLY FACTOR REFLECTING GEOMETRY, (4) THE AREA OF THE CONCRETE SURROUNDING EACH REINFORCING BAR, A, ALSO INFLUENCES THE CRACK WIDTH, (5) THE SIZE OF THE SIDE CRACK WIDTH IS REDUCED BY THE PROXIMITY OF THE COMPRESSION ZONE (NEUTRAL AXIS) IN FLEXURAL MEMBERS, (6) THE BOTTOM CRACK WIDTH IS INFLUENCED BY THE STRAIN GRADIENT FROM THE LEVEL OF THE STEEL TO THE TENSION FACE OF THE BEAM. /ACIJP/