Effect of Base Conditions in One-Dimensional Numerical Simulation of Seismic Site Response: A Technical Note for Best Practice

Abstract

The effects induced by the choice of numerical base conditions for evaluating local seismic response are investigated in this technical note, aiming to provide guidelines for professional applications. A numerical modelling of the seismic site response is presented, assuming a one-dimensional scheme. At first, with reference to the case of a homogeneous soil layer overlying a half-space, two different types of numerical base conditions, named rigid and elastic, were adopted to analyse the seismic site response. Then, geological setting, physical and mechanical properties were selected from Italian case studies. In detail, the following stratigraphic successions were considered: shallow layer 1 (shear wave velocity, VS, equal to 400 m/s), layer 2 (VS equal to 600 m/s) and layer 3 (VS equal to 800 m/s). In addition, real signals were retrieved from the web site of the Italian accelerometric strong motion network. Rigid and elastic base conditions were adopted to estimate the ground motion modifications of the reference signals. The results are presented in terms of amplification factors (i.e., ratio of integral quantities referred to free-field and reference response spectra) and are compared between the adopted numerical models.

Stochastic Approach for 2D Superficial Seismic Amplification Based on Quad4M; City of L’Aquila (Italy) Test Case

“…Both models were implemented with a transmitting boundary at the base so that the need to absorb artificial wave reflections was satisfied [35,36]. also depend on the element size of the grid.…”

Defining the Boundary Conditions for Seismic Response Analysis—A Practical Review of Some Widely-Used Codes

“…Finally, the input motion application is a function of the way the seismic bedrock is modeled, which can be deformable or rigid. In this latter hypothesis, the properties of the bedrock are not used in the analysis, but they are implicitly taken into account in the applied input motion [50,51].…”

“…The choice to model the seismic bedrock as rigid or deformable has a remarkable impact on the size of the analysis domain, boundary conditions at the base of the model and the type of input motion to apply [51,53]. The latter two will be discussed in Sections 4.4 and 4.5, respectively.…”

“…In the double frequency control approach, the lower frequency, f 1 , is usually set equal to the natural vibration frequency of the soil column (2.5 Hz in this case), while the higher one, f 2 , is a multiplier of f 1 [51]. In DEEPSOIL, a multiplier equal to 5 is recommended, while 3 is suggested in [12].…”

Fragility curves of masonry buildings in aggregate accounting for local mechanisms and site effects

“…Sabetta and Pugliese 1996), roughly from studies at national scale (e.g. Falcone et al 2021), and more accurately from seismic microzonation studies at city-scale (e.g. Pagliaroli et al 2020).…”