NPCA Staff Report
NPCA Director of Codes and Standards Daryl Burns recently authored an article about ACI 318-19 “Building Code Requirements for Structural Concrete” that was published in the August issue of Informed Infrastructure magazine.
Within the article, Burns breaks down the code and the minimum criteria it sets in relation to how it has had an overall negative effect on precast concrete production within the industry.
“One such section that has had a particularly negative impact on the precast industry is the change to the shear capacity of reinforced concrete beams and slabs,” Burns writes. “ACI Committee 318 … added a size effect factor (λs) that reduces the calculated shear capacity by approximately 30 to 40 percent, especially if the design section has a low reinforcement ratio (ρ) as is likely in double-tee flanges, other precast slab elements or cast-in-place slabs.
“The added size factor begins to effect slabs greater than 10 inches thick, which impacts buried structures such as manhole flattop slabs and vault top slabs. Based on the resounding successful performance of these buried slabs – with a previous required thickness of 12 inches or less for the last several decades – the precast industry strongly believes this shear capacity reduction modification should not apply to buried precast structure flat slabs.”
You can read the full article on Page 15 of the August 2022 edition of Informed infrastructure magazine or by clicking here.