Title: Concrete Q&A: Minimum Reinforcement in Elevated Water Storage Tanks
Publication: Concrete International
Q. Table 5.2 in “Guide for the Analysis, Design, and Construction of Elevated Concrete and Composite Steel-Concrete Water Storage Tanks (ACI 371R-08),”1 includes recommendations for minimum wall reinforcement. Under the heading, “Seismic coefficient SD1 < 0.20,” the table has two minimum reinforcement ratios for vertically oriented bars, depending on the “maximum compressive fiber stress based on actual axial plus flexure stress resulting on gross concrete section” fc. The ratio is 0.0015 when fc is below 1 ksi (7 MPa), but it’s 0.005 when fc is 1 ksi or more. Why is there such a jump when fc exceeds 1000 psi? Also, could you provide more details on the calculation of fc?
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