CONTROL OF FLEXURAL CRACK WIDTH IN CRACKED PRESTRESSED CONCRETE MEMBERS

Detailed crack-control procedures for prestressed concrete members that cracked under service loads are presented. The proposed method takes into consideration the bond characteristics of both prestressed and nonprestressed reinforcement in estimating the maximum crack width and can be applied to all practical combinations of prestressed reinforcement (pretensioned, post-tensioned, bonded or unbonded, strands, or wires) and nonprestressed reinforcement (deformed bars, strands, or wires). The method uses incremental steel stresses after decompression obtained by a rational cracked-section analysis. Design charts that facilitate one-step determination of steel stresses for rectangular, T-, and I-sections are presented. It is suggested that a more conservative limit on the maximum allowable crack-width to protect the prestressed tendons from the effects of corrosion (0.2 mm for exterior exposure and 0.3 mm for interior exposure) be adopted for effective crack control in cracked prestressed members.