Determination of Reinforced Fly Ash Concrete Columns’ Resistance Using Nonlinear Models of Materials

This article introduces experimental and analytical studies on the resistance under eccentric loads of reinforced fly ash concrete (RFAC) columns, in which fly ash (FA) is used to partially replace ordinary Portland cement (OPC) with a by-mass ratio of 20%. Based on experimental results of concrete specimens with mean 28-day cylinder strength of 30 MPa, modifications on simplified bi-linear and tri-linear models of stress-strain relationships of OPC concrete specified in the Russian and Vietnamese design standards are proposed. These nonlinear deformation models are incorporated into an analytical approach to establish the resistance of RFAC columns in the form of interaction surface, associated with an assessment method for safety factor based on the principle of inverse distance weighted average (IDWA). Parameters of the proposed analytical approach are determined by test results obtained from eight RFAC column specimens having 150 × 200 (mm) rectangular cross-section, 1600 mm-height, and 4Φ14 longitudinal rebars with yield strength of 362.6 MPa. In the tests, the specimens were loaded with uniaxial eccentricities ranging from 0 to 80 mm until failed. It is shown that with ε’b1 = 0.0022 and kE = 0.91, the corresponding safety factors of bi-linear and tri-linear models validated for the tested specimens are conservative and nearest to unity, proving that the proposed analytical approach is capable of closely predicting the RFAC columns’ resistance.