Minimum Reinforcing Requirements for Concrete Columns

This on-going investigation involves the response of reinforced concrete columns under sustained axial load. It is being conducted to establish the feasibility of reducing the minimum longitudinal reinforcing steel percentage as currently required by the ACI code. A review and discussion of previous studies is included.

A total of 38 reinforced concrete columns have been fabricated and are being maintained in reduced-humidity enclosures. Twenty-four of the 38 columns are being subjected to near-constant axial load. The remaining 14 are unloaded control specimens. Of the loaded columns, four are loaded with an axial eccentricity of approximately 10% of the column diameter.

The variables investigated were concrete strength and percentage of longitudinal reinforcement. It is intended that the columns will be maintained for a period of at least two years from the time of casting.

Preliminary experimental results were compared to those obtained from current predictive formulas for creep and shrinkage as outlined by ACI 209. Reasonable agreement was found.