An appraisal of the ACI strut efficiency factors

Abstract

The strut-and-tie modelling recommendations of the American Concrete Institute (ACI) 318-08 Appendix A are widely followed for the design of disturbed regions in concrete structures. In this investigation, an experimental appraisal of the ACI 318-08-recommended efficiency factors for prismatic and bottle-shaped struts has been carried out and inconsistency in the recommendations for bottle-shaped struts highlighted. It has been demonstrated that a bottle-shaped strut is in no way inferior to a prismatic strut in terms of strength and, consequently, the efficiency factor of bottle-shaped struts needs to be revised. An error in the ACI 318-08-recommended formulation for minimum effective transverse reinforcement in reinforced bottle-shaped struts is identified and corrected.