Time domain simulation of soil–foundation–structure interaction in non‐uniform soils

Abstract

SUMMARYPresented here is a numerical investigation of the influence of non-uniform soil conditions on a prototype concrete bridge with three bents (four span) where soil beneath bridge bents are varied between stiff sands and soft clay. A series of high-fidelity models of the soil-foundation-structure system were developed and described in some details. Development of a series of high-fidelity models was required to properly simulate seismic wave propagation (frequency up to 10 Hz) through highly nonlinear, elastic plastic soil, piles and bridge structure. Eight specific cases representing combinations of different soil conditions beneath each of the bents are simulated. It is shown that variability of soil beneath bridge bents has significant influence on bridge system (soil-foundation-structure) seismic behavior. Results also indicate that free field motions differ quite a bit from what is observed (simulated) under at the base of the bridge columns indicating that use of free field motions as input for only structural models might not be appropriate. In addition to that, it is also shown that usually assumed beneficial effect of stiff soils underneath a structure (bridge) cannot be generalized and that such stiff soils do not necessarily help seismic performance of structures. Moreover, it is shown that dynamic characteristics of all three components of a triad made up of earthquake, soil and structure play crucial role in determining the seismic performance of the infrastructure (bridge) system.

Discretization effects in the finite element simulation of seismic waves in elastic and elastic-plastic media

“…Since then, it has been believed that approximately ten nodes per wavelength are appropriate in most cases, whereas fewer than ten nodes are likely to result in undesired numerical attenuation/dispersion. Accordingly, suitable maximum grid spacing is usually determined by considering the minimum relevant wavelength (or highest frequency f max ) in the input signal [28]:…”

“…When linear elastic wave problems are considered, either time-domain or frequency-domain solutions may be sought, whereas time-domain approaches are usually needed in the presence of non-linearities (constitutive or geometrical). In this respect, it should be remarked that much interest in earthquake engineering is nowadays on non-linear wave phenomena, since they govern (i) the occurrence of natural catastrophes (e.g., landslides and debris flows) induced by soil instabilities, such as liquefaction and strain localization [18,24,63]; (ii) the interaction between geomaterials and man-made structures [13,16,20,28,53,59].…”

Time-Domain Soil-Structure Interaction Analysis of Nuclear Facilities

“…The assumption of equivalent linear behavior does not explicitly consider the nonlinear behavior of soil-structure systems such as the hysteretic behavior of soil. In the time domain analysis method [2][3][4][5][6] , the dynamic analysis is carried out by solving the equation of motion at each time step using a direct numerical integration scheme. In this approach, a large soil domain and a structural system is modeled as a single numerical model such that the inertial and kinematic interactions are inherently considered in the analysis.…”

Seismic response evaluation of an urban overpass

“…This is particularly important when the subsoil conditions change importantly over the length of the bridge (e.g. [9,10]). Seismic loading acting upon a soil-foundation system is the result of the interplay of earthquake incoming waves with the structure-swaying-produced waves, which can lead to beneficial or detrimental effects on the structure (e.g.…”

“…This approach requires more precise predictions of the structural response, using advanced numerical and analytical tools to conduct seismic soilstructure interaction, SSSI, analyses (e.g. [9,17]). This should include an accurate estimation of the support beams displacements, in both the transverse and longitudinal components, to ensure that relative movements between them will not separate the central beam from its supports (Figure 1), reducing the probability of collapse of the upper deck.…”