Maria Rossella Massimino

Experimental study in the shaking table of the input motion characteristics in the dynamic SSI of a SDOF model

In conventional seismic design the capacity of the system is generally exploited only at the superstructure level. However, soil non-linearity as well as soil-foundation interface non-linearity can be crucial in the seismic response of structures. The results of tests performed on physical models allow the main aspects of these interaction mechanisms to be identified and also provide a benchmark for subsequent theoretical or numerical analyses. The present paper deals with two shaking table tests performed at the University of Bristol’s EERC laboratory. The tests were performed on a physical model consisting of a Leighton Buzzard sand deposit and a one-storey steel model structure. Some of the test results are presented and discussed in terms of acceleration and displacement responses. Both time- and frequency-domain representations were adopted to highlight the influence of the frequency and amplitude of the input motion on the coupled and/or uncoupled response of the tested soil-structure system, as well as the effect of soil non linear behaviour.

Finite element modeling of a shaking table test to evaluate the dynamic behaviour of a soil‐foundation system

The deep investigation of soil‐foundation interaction behaviour during earthquakes represent one of the key‐point for a right seismic design of structures, which can really behave well during earthquake, avoiding dangerous boundary conditions, such as weak foundations supporting the superstructures. The paper presents the results of the FEM modeling of a shaking table test involving a concrete shallow foundation resting on a Leighton Buzzard sand deposit. The numerical simulation is performed using a cap‐hardening elasto‐plastic constitutive model for the soil and specific soil‐foundation contacts to allow slipping and up‐lifting phenomena. Thanks to the comparison between experimental and numerical results, the power and the limits of the proposed numerical model are focused. Some aspects of the dynamic soil‐foundation interaction are also pointed out.

Noto Cathedral: soil and foundation investigation

Abstract On 13th March 1996 the dome of the St. Nicolo Cathedral of Noto fell due to a post-seismic structural collapse. In order to study the soil–structure interaction a comprehensive laboratory and in situ investigation has been carried out to obtain a soil profile. In this paper the dynamic characterisation results and normalised laws are proposed to consider shear modulus decay and damping ratio increase with strain level. The existing foundations of the cathedral were investigated by means of excavations and tests on the stones and the mortar. In this way the foundations were subjected to visual inspections to detect their size and their embedment level. Now, the soil–foundation interaction has been analysed by means of the finite element code SOFIA, considering at this stage the superstructure weight through the influence area approach. In particular, the effects of the designed remedial work of the foundation have been studied, comparing the two configurations before and after the foundation improvement.

Numerical modelling of centrifuge tests on tunnel–soil systems

The number of tunnels in seismic regions has grown significantly in recent decades. It has usually been assumed that tunnels perform better than surface structures during seismic events. However, recent cases have shown that tunnels can be significantly damaged by seismic events. Thus, an evaluation of their response to earthquakes has become increasingly necessary. This paper presents a FEM blind prediction of centrifuge tests on a reduced scale tunnel. The main objective of the paper is to evaluate the numerical model that reproduces the response recorded in the centrifuge. The centrifuge tests involved a tunnel in dry sand. The numerical simulation was performed on the physical-scale model of the transverse direction of the tunnel, which is of prime importance, as it can show large stress–strain levels in the tunnel lining. The tunnel behaviour was assumed to be visco-linear-elastic, while the soil behaviour was assumed to be visco-elastic-perfectly plastic. The soil model parameters were calibrated on the basis of laboratory tests performed on the sand used for the test. The comparison between the experimental and numerical results is presented in terms of acceleration in the time and frequency domains. The experimental and numerical settlements of the sand surface and displacements of the sand-tunnel system, as well as the bending moments and hoop forces acting in the tunnel are also compared. Increments of the bending moments and hoop forces are also evaluated using the closed-form solution proposed by Wang (Seismic design of tunnels: a simple state-of-the-art design approach. Parson Brinckerhoff, New York, 1993) and Penzien (Earthq Eng Struct Dyn 29:683–691, 2000). A very good agreement between the experimental and numerical results is achieved in terms of horizontal acceleration time-histories and their Fourier spectra, as well as in terms of vertical displacements of the sand surface. Moderate differences exist between the experimental and numerical bending moments and hoop forces; experimental, numerical and analytical increments of the bending moments and hoop forces are in a quite good agreement with each other.

Evaluation of shallow foundation settlements by an elasto-plastic kinematic-isotropic hardening numerical model for granular soil

A numerical model based on a recent non-associative elasto-plastic model for sands (the Severn–Trent model), implemented in an FEM code, is presented. This model, which simultaneously takes into account the effects of the relative density D R and the mean effective stress level p reproduces the stress–strain behaviour of granular materials with reasonable accuracy. The constitutive relations are arranged in the form of a forward stress integration algorithm in a new subroutine. The algorithm is validated by comparison with the experimental results of several triaxial tests; the computed and experimental results are generally in good agreement for both loose and dense sands. Finally, the settlement of full-scale shallow foundations resting on a sand deposit is analysed; the numerical results obtained are very close to the experimental data.

Soil-Structure Interaction for Seismic Improvement of Noto Cathedral (Italy)

Noto Cathedral, one of the most famous example of Baroque architecture in Italy, was damaged by the December 13, 1990 earthquake (ML = 5.4) and because of the damage it partially collapsed on May 13, 1996. After the collapse, accurate investigations were performed on the structure and on the subsoil, in order to rebuild and improve this very significant religious heritage building.

Validation of a New Soil Constitutive Model for Cyclic Loading by FEM Analysis

Nowadays, there is an increasing need to understand the behaviour of geotechnical structures during earthquakes. The damage caused by the recent earthquakes has shown that the local geology and the geotechnical characteristics of the foundation soil can influence significantly the seismic response of structures. So, in order to correctly predict the behaviour of a structure subjected to an earthquake, it is necessary to focus attention on the dynamic soil behaviour. In general, very simple soil constitutive models are implemented in commercial codes. Several studies have shown that when shear strains in the soil are small, it is possible to use the elastic-linear model; for medium strains it is convenient to use equivalent linear or nonlinear models. Elastic-plastic models, incrementally nonlinear models or hypoplastic models can more accurately capture response for sites that experience higher strains. A recent elasto-plastic constitutive model including both isotropic and kinematic hardening has been implemented in a FEM code. The numerical results achieved by the new version of the FEM code, are discussed and validated by means of the comparison with laboratory experimental results involving sands of different relative densities. An interesting parametric analysis is also presented, in order to investigate the effects of the implemented constitutive model parameter variation in the soil cyclic behaviour.

Parametric analysis of the seismic response of coupled tunnel–soil–aboveground building systems by numerical modelling

Abstract During an earthquake, the presence of tunnels may affect the seismic wave propagation in the involving soil and in turns the response of aboveground structures. At the same time, the vibrations of aboveground structures may create a complex interaction with the tunnel and, consequently, they may modify the dynamic response of the tunnel. Most of the published papers considered only tunnel–soil systems or only soil−aboveground structures; analyses involving tunnel plus soil plus aboveground structures (full-coupled analyses) are still very rare. The present paper deals with a parametric analysis: starting from a real case-history regarding the Catania (Italy) underground network, and in particular a cross-section including an aboveground building, the depth of the tunnel, the position of the aboveground building and the seismic inputs were modified in order to study their effects on the dynamic tunnel–soil–aboveground building interaction. Thirty different recorded accelerograms were adopted. Results are reported in terms of accelerations in the time and frequency domains, as well as in terms of seismic bending moments and axial forces of the tunnel lining.

Site seismic response for a strategic building in the city of Messina by two-dimensional finite element analysis

It is well recognized that local seismic effects can exert a significant influence on the distribution of damages during earthquakes. Traditionally, these effects have been studied by means of simple one-dimensional (1-D) models of seismic wave propagation which take only the influence of the stratigraphic profile and soil/bedrock properties into account on the seismic response. Conversely, local effects derived from surface topography such as ridge, cliffs etc., which are typically two-dimensional (2-D) and three-dimensional (3-D) problems, have received less attention because of computational time, lack of experimental data and the need of more refined models. It is therefore of great interest to quantitatively evaluate the relative contribution on seismic response of stratigraphic as well as of topographic effects, which can be very different depending on the specific morphological conditions and geotechnical characteristics of the site.

Large scale soil-foundation-structure model in Greece: dynamic tests vs FEM simulation

This paper provides the results of FEM simulation of dynamic tests recently performed in Thessaloniki on a large-scale single-degree-of-freedom structure resting on a soft soil. The structure (named EuroProteas) was specifically designed to mobilize strong soilstructure interaction (SSI), being a particularly stiff structure founded on soft soil. It consists of a simple steel frame with removable X-bracings founded on a RC slab and supporting the superstructure mass of two RC slabs identical to the foundation slab. It is a totally symmetric structure. Subsoil stratigraphy and dynamic properties of the foundation soil are derived from extended geotechnical and geophysical surveys, including static and dynamic in-situ and laboratory tests. Extensive freeand forced-vibration tests were performed. This paper deals with one set of forced-vibration tests. An eccentric mass shaker was used as a source of harmonic excitation (f input = 3, 4.5, 5, 7 Hz and eccentricity 6.93kg-m) imposed on the roof of the structure. The structural response is recorded by seven accelerometers, five of which are located at the top of the roof slab and two at the top of the foundation slab. Soil response is recorded with seismometers installed on the free soil surface in both horizontal directions. Dynamic FEM modelling of the tests were conducted in the time and frequency domains in order to detect the main aspects of SSI, taking into account soil nonlinearity. Numerical and experimental results were extensively compared. Very interesting results were reached above all in terms of the effects of soil-foundation interface behaviour. 1347 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 1347-1359