Efficiency Factors for Plastic Design in Concrete: Influence of Brittleness in Compression, High Tech Concrete: Where Technology and Engineering Meet

A large number of design approaches for structural concrete rely on the applicability of limit analysis. This is for instance the case of bending and shear design in members with transverse reinforcement, where it is assumed that plastic compression fields develop in the concrete. The behaviour of concrete in compression, however, cannot be directly assumed as perfectly plastic. In order to consistently apply limit analysis, the compressive strength of concrete is usually reduced by a number of strength reduction factors. In this paper, the factor accounting for the brittle behaviour of concrete in compression is reviewed. The aim is to assess the need for a brittleness factor when determining the capacity of concrete columns subjected to pure compression. Theoretically, the need for this factor is justified as a reinforced column is a composite system, where an interaction (redistribution of forces) potentially occurs amongst the longitudinal bars and the concrete as well as with the transverse (confinement) reinforcement. A total of 207 specimens from the scientific literature were considered in this research. They were all characterized by low slenderness (no second order effects) and presented variable concrete compressive strength (24 to 200 MPa), cross-section (square or circular), longitudinal reinforcement ratio (0.8 to 6.8 %), transverse reinforcement ratio (0.1 to 3.5 %), tie arrangement and spacing, yield strength of the longitudinal reinforcement (260 to 820 MPa) and yield strength of the transverse reinforcement (300 to 1000 MPa). Their compressive capacity was evaluated according to a rigid-plastic approach as well as to EN1992-1-1:2004. On that basis, a series of conclusions are drawn on the need for a brittleness factor.