The American Concrete Institute (ACI) has issued revised recommendations for achieving quality, safety, and economy in forming and shoring operations. The new "Guide to Formwork for Concrete," prepared by ACI Committee 347, replaces a previous standard, ACI 347-78. Changes have been made in key areas to accommodate recent changes in concrete mixing and placing technology. Some of these changes are:
- Lateral pressure formulas have been changed to reflect the fact that although freshly placed concrete behaves much like a liquid, it is not a true fluid.
- A safety factor of at least 2.0 is now recommended for all form ties to match minimum safety factors.
- A minimum requirement of 70 percent of concrete design strength before supporting forms and shores can be removed from horizontal members has been added to encourage improved safety in field practice.
- Recommended tolerances for concrete construction have been deleted in preparing the new guide since ACI now has a separate standard listing dimensional and position tolerances.
- Provisions for "backshoring" have been inserted to replace "permanent shores," as a reflection of current field practice.