Proposed Minimum Steel Provisions for Prestressed and Nonprestressed Reinforced Sections

The current ACI code includes two separate provisions for minimum steel reinforcement: one for nonprestressed reinforced sections, and another for prestressed sections. For nonprestressed reinforced sections, the current minimum steel requirement is written in terms of geometric and material properties of the section. For prestressed concrete, the current provision is written in terms of the cracking moment of the section. Consequently, when bonded prestressing steel quantities are increased, the cracking moment of the section increases. Depending on the shape of the cross section and ultimate strength requirements, in certain instances it is possible that a section can contain a large volume of bonded prestressing steel and yet not meet the minimum reinforcement requirement. A parametric study of several cross sections was performed to investigate this behavior. This article describes an exact and unified solution approach for specifying minimum reinforcement for both nonprestressed and prestressed sections. A second parametric study to validate the proposed minimum steel provisions is also presented.