A refined Frequency Domain Decomposition tool for structural modal monitoring in earthquake engineering

Output-only structural identification is developed by a refined Frequency Domain Decomposition(rFDD) approach, towards assessing current modal properties of heavy-damped buildings(in terms of identification challenge), under strong ground motions. Structural responses from earthquake excitations are taken as input signals for the identification algorithm. A new dedicated computational procedure, based on coupled Chebyshev Type Ⅱ bandpass filters, is outlined for the effective estimation of natural frequencies, mode shapes and modal damping ratios. The identification technique is also coupled with a Gabor Wavelet Transform, resulting in an effective and self-contained time-frequency analysis framework. Simulated response signals generated by shear-type frames(with variable structural features) are used as a necessary validation condition. In this context use is made of a complete set of seismic records taken from the FEMA P695 database, i.e. all 44 "Far-Field"(22 NS, 22 WE) earthquake signals. The modal estimates are statistically compared to their target values, proving the accuracy of the developed algorithm in providing prompt and accurate estimates of all current strong ground motion modal parameters. At this stage, such analysis tool may be employed for convenient application in the realm of Earthquake Engineering, towards potential Structural Health Monitoring and damage detection purposes.     

Rocking damage‐free steel column base with friction devices: design procedure and numerical evaluation

Earthquake‐resilient steel frames, such as self‐centering frames or frames with passive energy dissipation devices, have been extensively studied during the past decade, but little attention has been paid to their column bases. The paper presents a rocking damage‐free steel column base, which uses post‐tensioned high‐strength steel bars to control rocking behavior and friction devices to dissipate seismic energy. Contrary to conventional steel column bases, the rocking column base exhibits monotonic and cyclic moment–rotation behaviors that are easily described using simple analytical equations. Analytical equations are provided for different cases including structural limit states that involve yielding or loss of post‐tensioning in the post‐tensioned bars. A step‐by‐step design procedure is presented, which ensures damage‐free behavior, self‐centering capability, and adequate energy dissipation capacity for a predefined target rotation. A 3D nonlinear finite element (FE) model of the column base is developed in abaqus . The results of the FE simulations validate the accuracy of the moment–rotation analytical equations and demonstrate the efficiency of the design procedure. Moreover, a simplified model for the column base is developed in OpenSees . Comparisons among the OpenSees and abaqus models demonstrate the efficiency of the former and its adequacy to be used in nonlinear dynamic analysis. A prototype steel building is designed as a self‐centering moment‐resisting frame with conventional or rocking column bases. Nonlinear dynamic analyses show that the rocking column base fully protects the first story columns from yielding and eliminates the first story residual drift without any detrimental effect on peak interstory drifts. The study focuses on the 2D rocking motion and, thus, ignores 3D rocking effects such as biaxial bending deformations in the friction devices. The FE models, the analytical equations, and the design procedure will be updated and validated to cover 3D rocking motion effects after forthcoming experimental tests on the column base. Copyright © 2017 John Wiley & Sons, Ltd.     

Bounds on the eigenvalues of the planetary-scale baroclinic instability problem

In the framework of the linear baroclinic instability problem for planetary geostrophic flows, bounds on the related complex eigenvalues are deduced. The main feature of this result is the independence of these bounds from the latitude and the density stratification, so that it generalizes the results of previous work on the subject.     

DmpIRFs and DmpST:DAMPE instrument response functions and science tools for gamma-ray data analysis

Observing GeV gamma-rays is an important goal of the DArk Matter Particle Explorer(DAMPE)for indirect dark matter searching and high energy astrophysics. In this work, we present a set of accurate instrument response functions for DAMPE(DmpIRFs) including the effective area, point-spread function and energy dispersion, which are crucial for gamma-ray data analysis based on statistics from simulation data. A dedicated software named DmpST is developed to facilitate the scientific analyses of DAMPE gamma-ray data. Considering the limited number of photons and angular resolution of DAMPE, the maximum likelihood method is adopted in DmpST to better disentangle different source components. The basic mathematics and framework regarding this software are also introduced in this paper.     

Landslides and other surface effects induced by the 1997 Umbria–Marche seismic sequence

This paper both describes and discusses landslides and other ground effects induced by the September–October 1997 seismic sequence, which struck the Umbria and Marche regions (Central Italy). Three main events occurred on 26 September at 00:33 and 09:40 GMT, and 14 October with magnitude M_w equal to 5.8, 6.0 and 5.4, respectively; furthermore hundreds of minor but significant events were also recorded. The authors examined an area of some 700 km² around the epicentre (Colfiorito). Primary and secondary effects were observed, including surface faulting phenomena, landslides, ground fractures, compaction and various hydrological phenomena. Surface evidence of faulting reactivation was found along the well-known capable faults, to a total length of ca. 30 km. Landslides, which were the most recurrent among the phenomena induced, consisted mainly of rock falls and subordinately of rotational and translational slides, which were generally mobilised by the inertia forces during the seismic motion. The percentage of reactivated old landslides decreased as the distance from the epicentral zone increased; a similar decrease had been observed for the 1980 Irpinia earthquake (Southern Italy). The ground fracture distribution was consistent with the regional structural setting and the general pattern of macroseismic field. Numerous episodes of hydrological changes were observed within the most severely damaged area. All this evidence confirms the relevance of the study of ground surface effects for achieving a more complete evaluation of seismic hazard.     

Mediterranean shelf-edge muddy contourites: examples from the Gela and South Adriatic basins

We present new evidence of shallow-water muddy contourite drifts at two distinct locations in the central Mediterranean characterized by a relatively deep shelf edge (between 170 and 300 m below sea level): the south-eastern Adriatic margin and the north-western Sicily Channel. The growth of these shelf-edge contourite drifts is ascribed to the long-term impact of the Mediterranean themohaline circulation. The Levantine Intermediate Water flows continuously, with annual or inter-annual variations, and affects the shelf edge and the upper slope in both study areas. In addition, the SW Adriatic margin is impinged by the seasonally modulated off-shelf cascading of North Adriatic Dense Water. This water mass has formed ever since the large Adriatic continental shelf was drowned by the post-glacial sea-level rise. It energetically sweeps the entire slope from the shelf edge to the deep basin. These bottom currents flow parallel or oblique to the depth contours, and are laterally constricted along markedly erosional moats aligned parallel to the shelf edge where they increase in flow velocity. The internal geometry and growth patterns of the shelf-edge contourites reflect changes in oceanographic setting affecting the whole Mediterranean Sea. In particular, seismic correlation with published sediment cores documents that these deposits are actively growing and migrating during the present interglacial, implying an enhancement in bottom-water formation during intervals of relative sea-level rise and highstand. Regardless of the specific mechanisms of formation, sediment drifts in both study areas have been affected by widespread thin-skinned mass-wasting events during post-glacial times. Repeated mass-transport processes have affected in particular the downslope flank of the shelf-edge contourite drifts, indicating that these muddy deposits are prone to failure during, or soon after, their deposition.     

Decoupling the effects of deforestation and climate variability in the Tapajós river basin in the Brazilian Amazon

Tropical river basins are experiencing major hydrological alterations as a result of climate variability and deforestation. These drivers of flow changes are often difficult to isolate in large basins based on either observations or experiments; however, combining these methods with numerical models can help identify the contribution of climate and deforestation to hydrological alterations. This paper presents a study carried out in the Tapaj?s River (Brazil), a 477,000 km² basin in South‐eastern Amazonia, in which we analysed the role of annual land cover change on daily river flows. Analysis of observed spatial and temporal trends in rainfall, forest cover, and river flow metrics for 1976 to 2008 indicates a significant shortening of the wet season and reduction in river flows through most of the basin despite no significant trend in annual precipitation. Coincident with seasonal trends over the past 4 decades, over 35% of the original forest (140,000 out of 400,000 km²) was cleared. In order to determine the effects of land clearing and rainfall variability to trends in river flows, we conducted hindcast simulations with ED2 + R, a terrestrial biosphere model incorporating fine scale ecosystem heterogeneity arising from annual land‐use change and linked to a flow routing scheme. The simulations indicated basin‐wide increases in dry season flows caused by land cover transitions beginning in the early 1990s when forest cover dropped to 80% of its original extent. Simulations of historical potential vegetation in the absence of land cover transitions indicate that reduction in rainfall during the dry season (mean of ?9 mm per month) would have had an opposite and larger magnitude effect than deforestation (maximum of +4 mm/month), leading to the overall net negative trend in river flows. In light of the expected increase in future climate variability and water infrastructure development in the Amazon and other tropical basins, this study presents an approach for analysing how multiple drivers of change are altering regional hydrology and water resources management.     

Discovery of cryptotephra at Middle–Upper Paleolithic sites Arma Veirana and Riparo Bombrini,Italy: a new link for broader geographic correlations

Chemical characterization of cryptotephra is critical for temporally linking archaeological sites. Here, we describe cryptotephra investigations of two Middle–Upper Paleolithic sites from north-west Italy, Arma Veirana and Riparo Bombrini. Cryptotephra are present as small (<100 µm) rhyolitic glass shards at both sites, with geochemical signatures rare for volcanoes in the Mediterranean region. Two chemically distinct shard populations are present at Arma Veirana (P1 and P2). P1 is a high silica rhyolite (>75 wt.%) with low FeO (<1 wt.%) and a K₂O/Na₂O > 1 and P2 is also a high silica rhyolite (>75 wt.%) but with higher FeO (2.33–2.65 wt.%). Shards at Riparo Bombrini (P3) are of the same composition as P1 shards at Arma Veirana, providing a distinct link between deposits at both sites. Geochemical characteristics suggest three possible sources for P1 and P3: eruptions from Lipari Island (56–37.7 ka) in Italy, the Acigöl volcanic field (200–20 ka) in Turkey and the Miocene Kirka-Phrigian caldera (18 Ma) in Turkey. Eruptions from Lipari Island are the most likely source for P1,3 cryptotephra. This study highlights how cryptotephra can benefit archaeology, by providing a direct link between Arma Veirana and Riparo Bombrini as well as other deposits throughout the Mediterranean.