Title:
Myth and Misinterpretation of "Overdesign"
Author(s):
Hover
Publication:
Web Session
Volume:
ws_S23_Hover.pdf
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
4/2/2023
Abstract:
Few terms in the concrete industry generate as much controversy, confusion, and downright disagreement as “Overdesign,” applied to the rational quality control provisions in the ACI 318 code. These provisions require that the average strength of concrete as delivered must exceed the required strength of the concrete used by the engineer to design the structure. If the average strength matched the required strength, cylinders would break low 50% of the time. These provisions are frequently misinterpreted as arbitrary conservatism that merely raises the bar and the aggravation for the concrete producer, increasing cost and carbon footprint in the process. Far from being arbitrary, the code provisions secure appropriate reliability of the structure while setting a value of required average strength that is unique to each concrete producer based on each producer’s unique quality control record. As improvements in concrete production and testing reduce within-batch and batch-to-batch variability, a concrete producer can reduce the required average concrete strength. Used in quality control and quality assurance programs for many industrial applications, these routine provisions came into the code upon adoption of the “limit-state” approach to design. That strategic transformation resulted in improved economy, constructability, and structural reliability. The presentation aims to explain the validity of the provisions using analogies such as catching a plane at the airport, target shooting, and playing poker.