Role of Nonlinearity in the Soil in Earthquake-Resistant Design of Structures

The nonlinearity of the soil may considerably affect the response of structures subjected to seismic events. This paper aims to show under which circumstances geometry, soil, and earthquake-type; the nonlinearity is important. A simple model based on a 1D shear column was developed to calculate the maximum shear strain (γ) in the soil subjected to earthquake excitation. It was found that γ is a function of peak ground acceleration PGA and the maximum horizontal ground displacement (∆). EC8 provides an expression for calculating ∆ that is independent of the soil thickness. It was found that this expression is conservative for shallow layers and underestimates γ for thick ones, as a result, improvements have been suggested. By performing several time history analyses, simple formulas are developed which enable the designer to assess when nonlinearity must be taken into account. Four curves based on soil thickness and peak ground acceleration have been introduced for different soil types (A, B, C, and D) using a limit value of γ = 10–4. These curves show that depending on the soil depth, the threshold acceleration of nonlinear soil behavior is around 0.48, 0.36, 0.29, and 0.10 m/s2 for soil types A, B, C, and D, respectively. Obviously, nonlinear analysis must be performed for shallow soil layers under moderate seismicity.