1,720,986 research outputs found
Thermodynamic-Based Macroelement Approach for Dynamic Analysis of Soil-Structure Systems
No full textNonlinear dynamic analysis is becoming a routinary approach for assessing the seismic performance of structures, especially in the case of soil-structure systems with marked nonlinear features or in earthquake prone regions. In these cases, the conventional substructure approach, based on linearity, loses its effectiveness. On the other hand, a fully coupled modelling cannot be considered as a suitable analysis method for extensive studies or in standard design. A compromise is therefore proposed: an approach with macroelements simulating the combined frequency- and amplitude-dependent response of geotechnical systems in the time-domain analysis of structures, preserving a limited computational effort. The thermodynamic inertial macroelements (TIMs) describe the multiaxial force-displacement relationships of the geotechnical systems, such as bridge abutments, shallow, deep and caisson foundations. These models are implemented in Open-Sees as a new class of multiaxial materials, that can be assigned to a modified ZeroLength finite element with fully coupled translational-rotational response. The constitutive responses are completely defined by two potential functions having a straightforward calibration. The application of the TIM approach is presented with reference to some soil-structure systems exhibiting highly nonlinear responses, showing the comparison with the results of fully coupled numerical representations developed in OpenSees
A Class of Thermodynamic Inertial Macroelements for Soil-Structure Interaction
Full text linkThe seismic performance of structures can be significantly influenced by the interaction with the foundation soils, with effects that depend on the frequency content and the amplitudes of the ground motion. A computationally efficient method to include these effects in the structural analysis is represented by the macroelement approach, in which a geotechnical system is modelled with a single macroelement that describes the generalized force-displacement relationship of the system. While this method has been mainly developed for shallow foundations, the present study proposes a class of macroelements representing the macroscopic response of different foundation types, including abutments, piled and caisson foundations. The generalized force-displacement relationships for these models are elastic-plastic and are derived using a rigorous thermodynamic approach. The plastic responses of the macroelements are bounded by the ultimate capacities of the geotechnical systems, while the inertial effects associated with the soil mass involved in the dynamic response of the structure are simulated by introducing appropriate participating masses. The macroelements are implemented in OpenSees; in this paper they are applied to assess the seismic performance of a tall viaduct showing highly nonlinear features
Generalised ultimate loads for pile groups
No full textFoundation piles can be used as a means for increasing the capacity of the foundations under static loads or, at the same time, can be regarded as an additional source of energy dissipation for the structure during strong motion. Under multi-axial loading, the ultimate capacity of a pile group is closely connected with the attainment of the flexural strength in the piles, which can in turn vary significantly according to the specific load path followed. Nonetheless, the design of piled foundations is still based on an independent evaluation of the vertical and horizontal capacities without accounting for the interaction between the several loads acting on the footing. To overcome this issue, in this paper a simplified numerical procedure for evaluating the capacity of piled foundations under multi-axial loading conditions is developed, which is based on the lower bound theorem of plastic limit analysis. On the basis of the numerical results, an analytical model of ultimate limit state surface is proposed, representing the force combinations that activate global plastic mechanisms of the soil–piles system. The identification of the ultimate surface necessitates a limited number of parameters having a clear physical meaning. The ultimate surface can lead to an optimised design of pile groups, allowing for a better control of the ultimate capacity as a function of the expected load patterns under static and dynamic conditions. In structural analysis, the ultimate surface can also be regarded as a bounding surface of a plasticity-based macroelement for piled foundations to account for the nonlinear features of the soil–pile system
IMPIEGO DELL'ARTROSCOPIA NEL TRATTAMENTO DEI POSTUMI FRATTURATIVI DELLA CAVIGLIA
No full textValutazione clinica mediante" scheda Faos" in pazienti sottoposti ad artroscopia di caviglia in esiti fratturativi della tibio-tarsica: dati pre e post trattamento a confronto
Modelling Nonlinear Static Analysis for Soil-Structure Interaction Problems
No full textNonlinear static analysis is a well-established seismic design method for structur-al systems. However, soil-structure interaction can significantly affect the earthquake-induced effects in the structural members. This is particularly evident for bridges with integral abutments, that imply the full transmission of the inertial effects developing in the soil to the entire structural system. In this view, this paper proposes an extension of the capacity spectrum method to soil-bridge systems as a simplified numerical procedure directly applicable in design. In the proposed method, the capacity of the system is evaluated through two different distributions of equivalent inertial forces applied to a computationally manageable soil-bridge domain, reproducing the deformation patterns associated with the dominant vibration modes. These modes are mainly controlled by the soil response and can be reasonably determined by a modal analysis of the soil deposit. The entire procedure is implemented in OpenSees and validated against the results of several dynamic analyses carried out on a reference case study
On the dynamic response of shallow foundations in saturated soils
Full text linkIn recent years, the development of macroelement approaches to include the macroscopic nonlinear response of soil-foundation systems in the assessment of structures is receiving an increasing interest by virtue of the minimal computational effort required. However, existing formulations commonly neglect any undrained or partly drained soil behaviour, that may be crucially important for simulating the response under dynamic loading. The present study provides an insight into the effects of the hydro-mechanical coupling of the soil on the macroscopic multiaxial cyclic response of shallow foundations. This is accomplished through a series of nonlinear transient analyses on a fully coupled soil-foundation numerical model implemented in OpenSees, providing an explicit description of the pore water pressure build-up induced by the nonlinear soil behaviour. The numerical study explores different assumptions for the hydraulic regime, from drained to undrained conditions. The effect of the volumetric-deviatoric coupling on the cyclic response of the reference foundation is examined, highlighting the key role played by the drainage conditions on the stiffness and dissipative features of the foundation system. The effect of non-linearity on the above effects is discussed and interpreted in terms of degradation of the system response at the macro scale
Impact of soil‐structure interaction on the effectiveness of Tuned Mass Dampers
Full text linkTuned Mass Dampers (TMDs) can represent an attracting solution to mitigate vibrations of a structure under seismic excitation, but their effectiveness can be considerably altered by the dynamic interaction with the foundation soil. The available design criteria for TMDs do not account for these effects and can therefore lead to a non-optimised structural performance. In this paper an investigation on the dynamic interaction of the TMD with the whole soil-structure system is presented, with the objective of highlighting the system parameters governing the response and the effectiveness of the device as seismic protection. An interpretative model of the soil-structure-TMD system expressed in a rigorous non-dimensional form is proposed, and an extensive global sensitivity analysis on its performance under harmonic loading is carried out. The identification of the typical performance regions shows that the seismic effectiveness of a TMD is mainly controlled by a limited number of parameters describing the structural behaviour and the soil-structure interaction, such as the structure-to-soil relative stiffness and those governing foundation rocking. The non-dimensional system parameters leading to either a favourable or detrimental effect on the TMD performance due to soil-structure interaction are also identified, and two design methodologies proposed in the literature are critically assessed in light of the framework proposed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A coupled study of soil-abutment-superstructure interaction
No full textThis paper presents a coupled numerical modelling of the soil-structure interaction for a multi-span girder bridge, inspired by a case study in Italy, to analyse the importance of the local dynamic response of the abutments in the seismic performance of the bridge. The full soil-bridge model was implemented in the analysis framework OpenSees, describing the mechanical behaviour of the foundation soils by means of an advanced constitutive model calibrated against experimental data. The results of the simulations demonstrate the relevance of the inertial effects, deriving from the dynamic response of the embankment, that enhance the non-linearity in the behaviour of the soil-abutment system. The present study is part of a wider research project concerning the dynamic behaviour of bridge abutments and its effects on the global structural performance. In this view, the proposed soil-bridge representation constitutes a benchmark for the validation of simpler analysis methods, using macro-element representations for the simulation of the dynamic response of the soil-abutment system
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