The 3D numerical simulation of near-source ground motion during the Marsica earthquake, central Italy, 100 years later

In this paper we show 3D physics-based numerical simulations of ground motion during one of the most devastating earthquakes in the recent Italian history, occurred on Jan 13, 1915, Marsica, Central Italy. The results provide a realistic estimate of the earthquake ground motion and fit reasonably well both the geodetic measurements of permanent ground settlement, and the observed macroseismic distribution of damage. In addition, these results provide a very useful benchmark to improve the current knowledge of near-source earthquake ground motion, including evaluation of the best distance metrics to describe the spatial variability of the peak values of ground motion, the relative importance of fault normal vs fault parallel components, the conditions under which vertical ground motion may prevail, as well as the adequacy of 1D vs 3D modelling of site amplification effects

Hybrid Galerkin numerical modelling of elastodynamics and compressible Navier–Stokes couplings: applications to seismo-gravito acoustic waves

We introduce a hybrid Galerkin modelling tool for the nonlinear acoustic and gravity wave propagation in planetary atmospheres coupled through topography to a solid medium. We rely on a 2-D spectral-element technique to model linear visco-elastic solid media and couple it to a discontinuous Galerkin method for the atmosphere modelled by the fully nonlinear Navier–Stokes equations. Significant benefits of such a method are, first, its versatility because it handles both acoustic and gravity waves in the same simulation, second, it enables one to observe nonlinear effects as convection or wave-breaking and, finally, it allows one to study the impact of ground-atmosphere coupling for waves propagating from seismic sources. Simulations are performed for 2-D isothermal atmosphere models with complex wind and viscosity profiles. We validate the computations by comparing them to finite-difference solutions, already validated in a previous paper. Specific benchmark validation cases are considered for both acoustic and gravity waves subject to viscosity variations, wind duct and nonlinear wave breaking. We apply this tool to study acoustic and gravity waves generated by a strong seismic source and its nonlinear breaking in the upper atmosphere

Inertial control of the mirror suspensions of the VIRGO interferometer for gravitational wave detection

In order to achieve full detection sensitivity at low frequencies, the mirrors of interferometric gravitational wave detectors must be isolated from seismic noise. The VIRGO vibration isolator, called 'superattenuator', is fully effective at frequencies above 4 Hz. Nevertheless, the residual motion of the mirror at the mechanical resonant frequencies of the system are too large for the interferometer locking system and must be damped. A multidimensional feedback system, using inertial sensors and digital processing, has been designed for this purpose. An experimental procedure for determining the feedback control of the system has been defined. In this paper a full description of the system is given and experimental results are presented.Comment: 17 pages, 11 figures, accepted for publication on Review of Scientific Instrument

Non-linear analysis of reinforced concrete structures subjected to transient forces

Abstract unavailable please refer to PD

Soil-structure interaction for bridge abutments: two complementary macro-elements

In recent years, the designers of girder bridges in seismic areas have frequently opted for a continuous structural scheme, in which the abutments are called to carry large seismic forces engaging the dynamic response of the soil-abutment system. It follows that the abutment response assumes a central role in evaluating the seismic performance of a bridge as an effect of its strong interaction with both the soil and the superstructure. This consideration introduces the cardinal question pursued in the present research: how and to what extent can the dynamic response of the abutments alter the global behaviour of a bridge and vice versa? To this end, this study proposes a method of analysis based on two complementary macro-elements, which simulate the salient aspects of the dynamic soil-abutment-superstructure interaction in the structural and geotechnical analyses of the bridge, preserving a manageable computational demand of the numerical soil-structure models. The two models consist of a macro-element of the soil-abutment system, developed as a useful tool for the structural analysis, and a macro-element of the superstructure to be included in the local model of the abutment instead. The internal responses of the macro-elements define a link between the dynamic response of the soil-abutment system and the global response of the superstructure, representing a step forward to a semi-direct approach for the study of the dynamic soil-structure interaction. The macro-elements were coded in the open-source finite element analysis framework OpenSees and validated against the results obtained with advanced nonlinear dynamic analyses of fully coupled soil-structure interaction models implemented in OpenSees

Application of Tuned Mass Dampers for Structural Vibration Control: A State-of-the-art Review

Given the burgeoning demand for construction of structures and high-rise buildings, controlling the structural vibrations under earthquake and other external dynamic forces seems more important than ever. Vibration control devices can be classified into passive, active and hybrid control systems. The technologies commonly adopted to control vibration, reduce damage, and generally improve the structural performance, include, but not limited to, damping, vibration isolation, control of excitation forces, vibration absorber. Tuned Mass Dampers (TMDs) have become a popular tool for protecting structures from unpredictable vibrations because of their relatively simple principles, their relatively easy performance optimization as shown in numerous recent successful applications. This paper presents a critical review of active, passive, semi-active and hybrid control systems of TMD used for preserving structures against forces induced by earthquake or wind, and provides a comparison of their efficiency, and comparative advantages and disadvantages. Despite the importance and recent advancement in this field, previous review studies have only focused on either passive or active TMDs. Hence this review covers the theoretical background of all types of TMDs and discusses the structural, analytical, practical differences and the economic aspects of their application in structural control. Moreover, this study identifies and highlights a range of knowledge gaps in the existing studies within this area of research. Among these research gaps, we identified that the current practices in determining the principle natural frequency of TMDs needs improvement. Furthermore, there is an increasing need for more complex methods of analysis for both TMD and structures that consider their nonlinear behavior as this can significantly improve the prediction of structural response and in turn, the optimization of TMDs

Wave Propagation in Rocks – Investigating the Effect of Rheology

Rocks exhibit beyond-Hookean, delayed and damped elastic, behaviour (creep, relaxation etc.). In many cases, the Poynting–Thomson–Zener (PTZ) rheological model proves to describe these phenomena successfully. A forecast of the PTZ model is that the dynamic elasticity coefficients are larger than the static (slow-limit) counterparts. This prediction has recently been confirmed on a large variety of rock types. Correspondingly, according to the model, the speed of wave propagation depends on frequency, the high-frequency limit being larger than the low-frequency limit. This frequency dependence can have a considerable influence on the evaluation of various wave-based measurement methods of rock mechanics. As experience shows, commercial finite element softwares are not able to properly describe wave propagation, even for the Hooke model and simple specimen geometries, the seminal numerical artefacts being instability, dissipation error and dispersion error, respectively. This has motivated research on developing reliable numerical methods, which amalgamate beneficial properties of symplectic schemes, their thermodynamically consistent generalization (including contact geometry), and spacetime aspects. The present work reports on new results obtained by such a numerical scheme, on wave propagation according to the PTZ model, in one space dimension. The simulation outcomes coincide nicely with the theoretically obtained phase velocity prediction