Optimal design of an equipment isolation system with nonlinear hysteretic behaviour

Vibration isolation is well recognized as an effective mitigation strategy for acceleration‐sensitive equipment subjected to earthquake. In the present paper, an equipment isolation system with nonlinear hysteretic behaviour is proposed and a methodology for the optimal design is developed. An integrable constitutive model, derived from the mathematical Duhem hysteresis operator, is adopted for the isolation system. The optimization procedure is defined through a dual‐criteria approach that involves a transmissibility criterion combined with an energy performance criterion: the former consists in limiting the absolute acceleration of the isolated equipment below an allowable threshold value; the latter, in maximizing the ratio between the energy dissipation due to hysteresis and the input energy to reduce the isolator displacements. The seismic effectiveness of the nonlinear hysteretic isolation system is numerically investigated under natural accelerograms with different frequency content and increasing levels of excitation. Both ground‐mounted and floor‐mounted equipment items are considered in the analyses; in the second case, the dynamic interaction between the equipment and its supporting structure is taken into account in the design of the isolation system, and its effects on the isolation performance and the structural response are discussed. Comparisons in terms of effectiveness and robustness with a linear isolation system with viscoelastic behaviour are eventually provided. Copyright © 2013 John Wiley & Sons, Ltd.     

Higher-order corrections to the relativistic perihelion advance and the mass of binary pulsars

We study the general relativistic orbital equation and using a straightforward perturbation method and a mathematical device first introduced by d’Alembert, we work out approximate expressions of a bound planetary orbit in the form of trigonometrical polynomials and the first three terms of the power series development of the perihelion advance. The results are applied to a more precise determination of the total mass of the double pulsar J0737-3039.     

Analytical prediction of ultimate moment and curvature of RC rectangular sections in compression

This paper presents closed form expressions linking the ultimate bearing capacity to the ultimate curvature of rectangular RC sections subjected to axial load and bending moment acting in one of the two symmetry planes of the section. With respect to possible simplified formulations the following effects are also considered: confinement of the concrete, hardening of the longitudinal reinforcement, and presence of reinforcing bars distributed orthogonally to the neutral axis. The formulation is proposed in dimensional terms after a preliminary definition of the geometrical and mechanical parameters governing the structural response of the class of sections considered. The analytical expressions derived using the proposed approach also allow one to determine the compression level that makes the ultimate bending moment maximum as well as to evaluate the curvature corresponding to the first yielding of the principal reinforcement in tension. Comparing this value of curvature with the ultimate one, an approximate estimation of the available ductility of curvature of the section can be made. The analytical procedure is validated by comparing the results with those obtained using a typical numerical approach. Some experimental results are also considered.     

Examining Granger causality between atmospheric parameters and radon

In this paper, we study the relationship between atmospheric parameters (i.e., temperature and humidity) and radon data. We use the linear Granger causality in order to observe possible connections, on short and mid time scale periods, between radon time series and meteorological parameters that strongly influence radon emissions. The analysis suggests radon emission is not affected by these atmospheric parameters on short periods, while there is an evidence of Granger causality on mid periods.     

Bombs behaving badly: unexpected trajectories and cooling of volcanic projectiles

We collected thermal infrared video of two explosive eruptions at Stromboli in June 2008 and manually traced the trajectories of 95 particles launched during two eruptions. We found that 10–15?% of the analyzed trajectories deviated from predicted curves due to collisions, causing one particle to travel horizontally more than twice as far as expected. Furthermore, we observed an oscillatory cooling behavior for the airborne pyroclasts, with a median period of 0.46?s. Measured cooling was typically much faster than model-predicted cooling with discrepancies of up to 40?% between measured cooling and theoretical modeling. We interpret the measured cooling curves as resulting from the spinning and twisting and tearing of particles during travel: the periodic re-exposing of the hotter core of the pyroclasts to the atmosphere may cause the observed oscillations, and the spinning may accelerate cooling by enhancing convective heat transfer. Current volcanic trajectory and cooling models do not account for projectile collisions, spinning, or tearing and can thus severely underestimate the maximum landing distance and cooling rates of large pyroclasts.     

Frequency of debris flows and their relation with precipitation: A case study in the Central Alps, Italy

Debris flows are very important and widespread mass movements, and represent a remarkable geomorphological hazard. This research deals with debris flows in an alpine environment, studied using dendrogeomorphological dating techniques, outlining their relation with precipitation, and analysing possible changes in their frequency and intensity over time. The study area is the upper Valle del Gallo (Northern Italy), a typical high mountain environment dominated by mass wasting processes, where many debris-flow fans occupy the valley bottom. Dendrogeomorphological research was conducted on twelve of these fans and two channels located on slopes. Tree growth anomalies (abrasion scars, compression wood and abrupt growth changes) were used as dating methods. Two hundred and thirty nine debris debris-flow events between 1875 and 2003 were dated using 757 trees (Pinus montana Mill.). Analysis between dated events and precipitation suggests that debris flows in the study area could be triggered by 20–30 mm of rain concentrated in a few hours. The debris-flow frequency tends to increase gradually, but the highest value seems to have occurred in the period 1974–1983. This trend agrees with the historical occurrence of flooding events in Northern Italy as inferred by literature, and with similar studies conducted in the Swiss Alps. The results of this research are intended as a contribution for understanding the response of geomorphological processes to climatic changes.     

Modelling river and riparian vegetation interactions and related importance for sustainable ecosystem management

We discuss the importance of modelling riparian vegetation and river flow interactions under differing hydrologic regimes. Modelling tools have notable implications with regard to the understanding of riverine ecosystem functioning and to promote sustainable management of water resources. We present both deterministic and stochastic approaches with different levels of simplification, and discuss their use in relation to river and vegetation dynamics at the related scale of interest. We apply such models to both meandering and braided rivers, in particular focusing on the floodplain dynamics of an alpine braided river affected by water impoundment. For this specific case we show what the expected changes in riparian vegetation may be in a ‘controlled release’ scenario for the postdam river Maggia, Switzerland. Finally, the use of these models is discussed in the context of current research efforts devoted to river restoration practice.     

Interpretation of regional aeromagnetic data by the scaling function method: the case of Southern Apennines (Italy)

A complex aeromagnetic anomaly in Southern Apennines (Italy) is analysed and interpreted by a multiscale method based on the scaling function. We use multiscale methods allowing analysis of a potential field along ridges, which are lines defined by the position of the extrema of the field at the considered scales. The method developed and applied in this paper is based on the study of the scaling function of the total magnetic field. It allows recovering of source parameters such as depth and structural index. The studied area includes a Pleistocene volcanic structure (Mt. Vulture) whose intense dipolar anomaly is superimposed on a longer wavelength regional anomaly. The interpretation of ridges of the modulus of the analytic signal at different altitude ranges allows recognition of at least three distinct sources between about 5 km and 20 km depth. Their interpretation is discussed in light of borehole data and other geophysical constraints. A reasonable geological model for these sources indicates the presence of intrusions, probably linked to the past activity of Mt. Vulture.     

The role of rainfall in the landslide hazard: the case of the Avigliano urban area (Southern Apennines, Italy)

Mass movements varying in type and size, some of which are periodically reactivated, affect the urban area of Avigliano. The disturbed and remoulded masses consist of sandy–silty or silty–clayey plastic material interbedded with stone fragments and conglomerate blocks. Five landslides that were markedly liable to rainfall-associated instability phenomena were selected.

The relationships between landslides and rainfall were investigated using a hydrological and statistical model based on long-term series of daily rainfall data. The model was used to determine the return period of cumulative daily rainfall over 1–180 days. The resulting hydrological and statistical findings are discussed with the aim of identifying the rainfall duration most critical to landslides.

The concept of a precipitation threshold was generalized by defining some probability classes of cumulative rainfall. These classes indicate the thresholds beyond which reactivation is likely to occur. The probability classes are defined according to the return period of the cumulative rainfall concomitant with landslide reactivation.     

The Finero phlogopite-peridotite massif: an example of subduction-related metasomatism

The Finero peridotite massif is a harzburgite that suffered a dramatic metasomatic enrichment resulting in the pervasive presence of amphibole and phlogopite and in the sporadic occurrence of apatite and carbonate (dolomite)-bearing domains. Pyroxenite (websterite) dykes also contain phlogopite and amphibole, but are rare. Peridotite bulk-rock composition retained highly depleted major element characteristics, but was enriched in K, Rb, Ba, Sr, LREE (light rare earth elements) (La_N/Yb_N = 8–17) and depleted in Nb. It has high radiogenic Sr (⁸⁷Sr/⁸⁶Sr₍₂₇₀₎ = 0.7055–0.7093), low radiogenic Nd (ɛNd₍₂₇₀₎= −1 to −3) and EMII-like Pb isotopes. Two pyroxenite – peridotite sections examined in detail show the virtual absence of major and trace element gradients in the mineral phases. In both rock types, pyroxenes and olivines have the most unfertile major element composition observed in Ivrea peridotites, spinels are the richest in Cr, and amphibole is pargasite. Clinopyroxenes exhibit LREE-enriched patterns (La_N/Yb_N ∼16), negative Ti and Zr and generally positive Sr anomaly. Amphibole has similar characteristics, except a weak negative Sr anomaly, but incompatible element concentration ∼1.9 (Sr) to ∼7.9 (Ti) times higher than that of coexisting clinopyroxene. Marked geochemical gradients occur toward apatite and carbonate-bearing domains which are randomly distributed in both the sections examined. In these regions, pyroxenes and amphibole (edenite) are lower in mg## and higher in Na₂O, and spinels and phlogopite are richer in Cr₂O₃. Both the mineral assemblage and the incompatible trace element characteristics of the mineral phases recall the typical signatures of “carbonatite” metasomatism (HFSE depletion, Sr, LILE and LREE enrichment). Clinopyroxene has higher REE and Sr concentrations than amphibole (^amph/cpxD_REE,Sr = 0.7–0.9) and lower Ti and Zr concentrations. It is proposed that the petrographic and geochemical features observed at Finero are consistent with a subduction environment. The lack of chemical gradients between pyroxenite and peridotite is explained by a model where melts derived from an eclogite-facies slab infiltrate the overhanging harzburgitic mantle wedge and, because of the special thermal structure of subduction zones, become heated to the temperature of the peridotite. If the resulting temperature is above that of the incipient melting of the hydrous peridotite system, the slab-derived melt equilibrates with the harzburgite and a crystal mush consisting of harzburgite and a silica saturated, hydrous melt is formed. During cooling, the crystal mush crystallizes producing the observed sequence of mineral phases and their observed chemical characteristics. In this context pyroxenites are regions of higher concentration of the melt in equilibrium with the harzburgite and not passage-ways through which exotic melts percolated. Only negligible chemical gradients can appear as an effect of the crystallization process, which also accounts for the high amphibole/clinopyroxene incompatible trace element ratios. The major element refractory composition is explained by an initially high peridotite/melt ratio. The apatite, carbonate-bearing domains are the result of the presence of some CO₂ in the slab-derived melt. The CO₂/H₂O ratio in the peridotite mush increased by crystallization of hydrous phases (amphibole and phlogopite) locally resulting in the unmixing of a late carbonate fluid. The proposed scenario is consistent with subduction of probably Variscan age and with the occurrence of modal metasomatism before peridotite incorporation in the crust. Received: 20 July 1998 / Accepted: 28 October 1998