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The seismic actions transmitted to a structure can be limited by inserting a frictional system between the foundation and the underlying soil. This allows a controlled sliding when the seismic forces reach a given critical value, that should be chosen to provide a desired seismic performance of the structure. Although this type of dissipative foundation has recently been adopted for the towers of two long-span bridges, its design still requires the development of a clear and robust design approach. In this view, the present paper studies the response of dissipative foundations, developing a generalised non-dimensional formulation that can be useful for design. The dynamic response of the foundation is analysed using a Newmark rigid block model, that is modified to account for the multi-directionality of the ground motion and to include a simplified description of the dynamic response of the superstructure. The main factors affecting the dynamic response of the dissipative system are highlighted through an extensive parametric study, leading to the definition of an optimised design approach of the dissipative foundation. • The paper studies the response of friction dissipative foundations of the type adopted in two recent long-span bridges. • A modified dynamic sliding-block model is developed to carry out an extensive parametric study. • The model results are expressed in a rigorous non-dimensional form. • The results show that the seismic performance of the system depends on the features of the entire soil-structure system. • A design approach is proposed to maximise the seismic efficiency of the dissipative foundation. [ABSTRACT FROM AUTHOR]

• A roadway tunnel was damaged by the Norcia Earthquake, in Italy. • A back-analysis of the damage was carried out with an original methodology. • The analysis was based on the available seismic records of the same event. • The damage was principally caused by seismic load acting on a lining with a reduced thickness. • The dynamic response of the lining contributed substantially to the observed damage. This paper deals with the interpretation of the damage originated by the 2016 Norcia earthquake, Italy, in a deep tunnel excavated in a calcareous rock mass. A careful investigation of the damage pattern, together with the availability of seismic signals recorded in the vicinity of the tunnel during the earthquake, prompted a back-analysis of the observed phenomenon. The study hinged on a combination of site response analyses, simulation of the tunnel construction, and computation of the effect of the earthquake on the tunnel lining. Specifically, the damage caused by the earthquake in the tunnel lining was evaluated both with a decoupled procedure, based on equivalent static loading, and with a fully coupled dynamic analysis of the soil-structure interaction. The results obtained from the back-analysis were in a good agreement with the observations, and contributed to evidence the main causes of the damage, related to the specific geometry and to the dynamic response of the lining. The approach used in the paper, validated for the present case study through the comparison with the observed tunnel damage, may be useful to assess the seismic vulnerability of existing tunnels and for the seismic design of new underground structures. [ABSTRACT FROM AUTHOR]

A hyperplastic macroelement is proposed as an efficient means for simulating nonlinear and multi-directional soil-piles interaction in the nonlinear analysis of structures. The macroelement relates the generalised forces exchanged between the superstructure and the foundation to the corresponding displacements and rotations of the foundation raft. The inertial effects developing under dynamic loading can be reproduced by coupling the macroelement with the participating masses of the soil-foundation system, obtainable with a modal identification of the pile group. Failure conditions of the foundation are described by a hyper-ovoidal ultimate limit state surface in the force space, which is calibrated through standardised procedures. The plastic behaviour, controlled by a series of yield surfaces with kinematic hardening, produces the desired directional coupling and allows to model the cyclic response and the irreversible deformation of the foundation. The macroelement is implemented in the analysis framework OpenSees for a prompt use in earthquake engineering applications. Its predictions under monotonic loads are validated against experimental data and advanced, fully coupled numerical modelling, while its dynamic response is tested on a reference case study. [ABSTRACT FROM AUTHOR]

This paper analyses the dynamic behaviour of a seismic isolation technology adopted for the foundations of the towers of two recent long-span bridges, consisting of a dissipative layer of granular soil placed at the contact of the foundation caisson with a group of foundation piles. The fundamental aspects of this isolation device is studied through a three-dimensional modified Newmark model that accounts for the multi-directionality of the seismic motion and includes a simplified description of the dynamic response of the superstructure. This simplified model is expressed in a rigorous non-dimensional formulation and is validated against the results of three-dimensional dynamic analysis of the soil-structure interaction for a specific case of a suspension bridge. Taking advantage of the non-dimensional formulation of the simplified dynamic model, a parametric study of general validity is carried out, that highlights the most significant factors influencing the performance of the dissipative device. [ABSTRACT FROM AUTHOR]

This study deals with the detrimental effects of consolidation on the behaviour of excavations carried out in fine-grained soils. With the aim of reproducing the main aspects of the mechanical behaviour of medium-soft clays, an advanced constitutive model was adopted, which is based on bounding surface plasticity and can take into account the damage to the soil microstructure induced by plastic strains. In a first stage of the work, this constitutive model was implemented into a finite element program, and its response was studied through a series of single-element tests, evidencing the effect of the different soil parameters and initial conditions. In the present paper, the constitutive model was used to simulate the behaviour of an idealised excavation, studying the effect of the progressive dissipation of the excess pore water pressures generated during the excavation stages. It was found that, under certain conditions, the initial degree of structure can be progressively lost during consolidation. This detrimental effect produces significant deformation increments and in some cases can drive the system to collapse. [ABSTRACT FROM AUTHOR]

Abstract: This paper illustrates an approach to the study of the seismic soil–structure interaction that was developed at the verification stage of the design of the Messina Strait Bridge in order to validate its seismic behaviour. It consisted of a series of two-dimensional, plane strain numerical analyses on models that included, in addition to the embedded foundation elements, a simplified structural description of the bridge towers: simplified structural models were specifically designed to reproduce the first vibrations modes of the towers, that were deemed to have the most significant influence on the system's dynamic response. Non-linear dynamic analyses were carried out in the time domain, studying the effects of two different natural records, each characterised by three orthogonal components of the soil motion. In the first part of the paper, essential information is provided about the foundations layout, the main properties of the foundation soil resulting from the in situ and laboratory investigation, and the assessment of the liquefaction potential. Then, the numerical models are discussed in some detail, with an emphasis on the modelling of the soil and of the structural elements. For sake of conciseness, details are provided only for one of the two shores. The results obtained with the present approach shed some light on the complex coupling between the soil's and the structure's behaviour, evidencing the significant role that the embedded, massive foundations of the bridge play in the dynamic response of the system. The computed time-histories of the displacements of the foundation elements are used to assess the seismic performance of the bridge. [Copyright &y& Elsevier]

Under seismic conditions a bridge abutment can transfer significant inertial effects to the superstructure due to its interaction with a large volume of soil. These effects can lead to a marked dynamic amplification of the abutment response that should be accounted for in bridge design. In order to quantify these effects, we present analytical solutions for the modal characteristics of the soil-abutment system at small strains, expressed in terms of the vibration periods and mass participation factors for the approach embankment considering different directions of motion. The effect of nonlinear soil behaviour is also investigated through nonlinear numerical analyses of the soil-abutment system in OpenSees, which establish the dependence of the vibration periods on the intensity of the external perturbation. The numerical results were used as a benchmark to validate the analytical predictions at small strains; they can also provide some indication on the applicability of the analytical formulation at medium and large strain levels. The proposed method of dynamic identification can be used as a tool to evaluate the dynamic characteristics of bridge abutments, which can be in turn regarded as the inertial features of macroelement representations for abutments in the structural analysis of bridges. • Analytical approach for the dynamic identification of the soil-abutment system. • Nonlinear soil behaviour investigated through numerical soil-abutment interaction models. • Inertial effects in the embankment control the dynamic response of the abutment. • Inertial effects controlled by the fundamental modes of the embankment. • Lengthening of the dynamic response of the soil-abutment system function of the load direction. [ABSTRACT FROM AUTHOR]

This paper studies the seismic response of a foundation pile embedded in a saturated coarse-grained deposit. The pile response is examined through a series of three-dimensional dynamic finite element analyses incorporating an advanced plasticity soil model and implementing a fully coupled interaction between the soil skeleton and the pore fluid. The study is mainly focused on the development of the internal forces in a pile immersed into a deposit including two soil layers with a different stiffness, and accounts for the development of excess pore water pressures during the seismic motion. The effects of the initial porosity and of the permeability of the soil layers are investigated, together with the effects of changing the pile length, the pile diameter, and the boundary condition at the top of the pile. Finally, the results of the finite element simulations are used as a benchmark to evaluate the capability of a number of simplified predictive methods and to provide guidance for their implementation. [ABSTRACT FROM AUTHOR]