Effect of Normalization Approaches on Shear Modulus Degradation Curve of Saturated Sand in Shaking Table Tests

Shear modulus degradation curves are fundamental inputs in nonlinear site response analyses and are conventionally normalized by the small-strain shear modulus, Gmax, defined at shear strains on the order of γ ≈ 10−4%. In shaking table experiments, however, reliable measurements at very small strains are often unattainable due to instrumentation resolution and strain demand limitations. Consequently, normalization is frequently performed using the shear modulus at a higher reference strain (γ = 0.01%). The impact of this alternative normalization on the resulting shear modulus degradation relationship has not been systematically evaluated. This study investigates the influence of normalization strain level on shear modulus degradation behavior using stress–strain relationships reconstructed from shaking table acceleration records. The shear modulus values were computed from individual hysteresis loops. The shear modulus normalized by Gmax estimated from empirical correlations was compared with the shear modulus normalized by its value at γ = 0.01% directly obtained from shaking table measurements. Results indicate that normalization at γ = 0.01% produces slightly lower normalized modulus values for shear strains exceeding 0.01% compared with the curve normalized by Gmax. Normalization using Gγ=0.01% resulted in reduced scatter and uncertainty.