Use of major and selected trace elements to describe mixing processes in a water reservoir

Data on temperature, major constituents and some trace elements, measured in the dissolved and particulate phases, were used to identify the hydrodynamics of a reservoir (the Bicaz reservoir, Romania). Results revealed that the reservoir experiences two thermal stratifications per year (summer and winter). However, the summer stratification is delayed by the high river inflow of June–July. Two layers were identified, a surface and a deep layer, whose location and impact vary with time. The surface layer originates from the river inflow (intrusion layer) and the deep current is produced by the outflow (velocity current). According to season, the river inflow either supplies the deep current or remains recordable up to the dam. Consequently, the structure of the water column, and thus the biogeochemical processes within it, are governed both by thermal stratification and by these layers.     

Morphology and environmental impact of the Colţi–Aluniş landslide (Curvature Carpathians), Romania

The May–August 2005 heavy rainstorm events in Romania triggered a large number of geomorphic hazards of great magnitude, consisting of primarily floods and landslides. Some of the most affected regions were the Curvature Carpathians and Subcarpathians. This paper addresses the effects of rainfall on slopes, especially in the middle sector of the Sibiciu basin (the Buzău Carpathians) outlining the significant landslide damage along the road connecting the Colţi and Aluniş villages. The landslides are analyzed in terms of geologic, geomorphic and engineering geologic features, focusing on the Colţi–Aluniş landslide which had the greatest impact on the road displacement. The related environmental and social impacts are also discussed.     

Landslide susceptibility assessment using the bivariate statistical analysis and the index of entropy in the Sibiciu Basin (Romania)

The Sibiciu Basin is located in Romania between the Buzău Mountains and the Buzau Subcarpathians (Curvature Carpathians and Subcarpathians). The geology of the basin consists of Paleogene flysch deposits represented by an alternation of sandstones, marls, clays and schists and Neogene deposits represented by marls, clays and sands. The area is affected by different types of landslides (shallow, medium-deep and deep-seated failures). In Romania, in the last decades, direct and indirect methods have been applied for landslide susceptibility assessment. The most utilized before 2000 were based on qualitative approaches. This study evaluates the landslide susceptibility in the Sibiciu Basin using a bivariate statistical analysis and an index of entropy. A landslide inventory map was prepared, and a susceptibility estimate was assessed based on the following parameters which influence the landslide occurrence: slope angle, slope aspect, curvature, lithology and land use. The landslide susceptibility map was divided into five classes showing very low to very high landslide susceptibility areas.     

Isotopic climate record in a Holocene stalagmite from Ursilor Cave (Romania)

The PU‐2 stalagmite from Ursilor Cave provides the first dated Romanian isotope record for the Holocene. The overall growth rate of the speleothem was 3.5 cm kyr^?1, corresponding to a temporal resolution of 142 y between each isotope analysis. The ‘Hendy’ tests indicate that isotopic equilibrium conditions occurred during the formation of PU‐2, and hence that it is suitable for palaeoclimatic studies. The relationship between δ¹⁸O and temperature was found to be positive. This can be interpreted either as rain‐out with distance from the west‐northwest ocean source of evaporation or shifts in air mass source with changing North Atlantic Oscillation indices. Applying five U–Th thermal ionisation mass spectrometric (TIMS) dates to a 17.5 cm isotope profile (δ¹⁸O and δ¹³C) along the stalagmite growth axis enabled a tentative interpretation of the palaeoclimate signal over the past 7.1 kyr. Spikes of depleted isotopic δ¹⁸O values are centred near ca. 7, ca. 5.2 and ca. 4 ka, reflecting cool conditions. The record shows two warm intervals between ca. 3.8 and ca. 3.2 ka (the maximum warmth) and from ca. 2 to ca. 1.4 ka, when the δ¹⁸O values were less negative than present. The ‘Holocene Climate Optimum’ spanning the time interval from ca. 6.8 to ca. 4.4 ka is not well expressed in the PU‐2 stalagmite. Individual spikes of lighter δ¹³C are interpreted as indicative of periods of heavy rainfall, at ca. 7, ca. 5.5, and ca. 3.5 ka. The overall trend to lighter δ¹³C in the PU‐2 stalagmite may reflect a gradual decrease in water–rock interaction. The results demonstrate that the effect of North Atlantic oceanic changes extended to the investigated area. Nevertheless, some differences in temporal correlation and intensity of stable isotopic response to these climatic events have been found, but the exact nature of these differences and the underlying mechanism is yet to be determined. Copyright © 2002 John Wiley & Sons, Ltd.     

Mechanisms to limit higher mode effects in a controlled rocking steel frame. 2: Large‐amplitude shake table testing

This paper presents the results of 56 large‐amplitude shake table tests of a 30% scale eight‐storey controlled rocking steel frame. No significant damage or residual deformations were observed after any of the tests. The frame had four possible configurations on the basis of combinations of two higher mode mitigation mechanisms. The first mitigation mechanism was formed by allowing the upper section of the frame to rock, so as to better control the mid‐height overturning moment. The second mitigation mechanism was formed by replacing the conventional first‐storey brace with a self‐centering energy dissipative (SCED) brace, so as to better control the base shear. The mechanisms had little effect during records where higher mode effects were not apparent, but they substantially reduced the shear and overturning moment envelopes, as well as the peak floor accelerations, during more demanding records. The reduction in storey shears led to similarly reduced brace force demands. Although the peak force demands in the columns were not reduced by as much as the frame overturning moments, using an upper rocking joint allowed the column demands to be estimated without the need to assume a lateral force distribution. The tests demonstrated that multiple force‐limiting mechanisms can be used to provide better control of peak seismic forces without excessive increases in drift demands, thus enabling more reliable capacity design. These results are expected to be widely applicable to structures where the peak seismic forces are significantly influenced by higher mode effects. Copyright © 2012 John Wiley & Sons, Ltd.     

Macroseismic field of the October 27, 2004 Vrancea (Romania) moderate subcrustal earthquake

On October 27, 2004, a moderate size earthquake occurred in the Vrancea seismogenic region (Romania). The Vrancea seismic zone is an area of concentrated seismicity at intermediate depths beneath the bending area of the southeastern Carpathians. The 2004 M _w?=?6 Vrancea subcrustal earthquake is the largest seismic event recorded in Romania since the 1990 earthquakes. With a maximum macroseismic intensity of VII Medvedev–Sponheuer–Kárník (MSK-64) scale, the seismic event was felt to a distance of 600 km from the epicentre. This earthquake caused no serious damage and human injuries. The main purpose of this paper is to present the macroseismic map of the earthquake based on the MSK-64 intensity scale. After the evaluation of the macroseismic effects of this earthquake, an intensity dataset has been obtained for 475 sites in the Romanian territory. Also, the maximum horizontal accelerations recorded in the area by the K2 network are compared to the intensity values.     

Characterizing acceleration spikes due to stiffness changes in nonlinear systems

Recent studies have reported very large accelerations after stiffness changes in nonlinear systems, particularly self‐centering systems. Some have attributed these accelerations to numerical modelling choices and have assumed that they could be eliminated if the modelling were refined. Others have concluded that self‐centering systems generally have much larger peak accelerations than more traditional systems. This paper demonstrates that accelerations at changes in stiffness are caused by physical phenomena but may be amplified by modelling decisions. This is done by examining the response of a two‐degree‐of‐freedom system after a change in stiffness and by developing a closed‐form mathematical model to characterize this response. The equation shows that acceleration spikes should be expected near small masses and near nonlinear springs that are initially nearly rigid, particularly when those springs change from low stiffness to high stiffness while moving at a high velocity. These acceleration spikes depend on system properties that are often not known precisely, so without physical testing, analytical estimates of the accelerations that occur in nonlinear systems after stiffness changes should be treated with skepticism. Copyright © 2010 John Wiley & Sons, Ltd.     

Pre-Observational Evolution of Surface Temperature in Romania as Inferred from Borehole Temperature Measurements

Temperature data from nine boreholes in the Carpathian orogen in Romania were used to obtain information on the ground surface temperature history (GSTH) in the last 250?years. The temperature measurements were taken with a thermistor probe (sensitivity in the 10 mK range) using the stop-and-go technique, at 10 m intervals, in the depth range of 20–580?m. The least squares inverse modelling approach of Tarantola and Valette (J Geophys 50:159–170, 1982) was used to infer the GSTH. Long-term air temperature records available from the Romanian weather station network were used as a comparison term for the first 100–150?years of the GSTH, and as a forcing function in a POM-SAT model that combines borehole temperature profiles (BTPs) and meteorological time series (surface air temperature, SAT) to produce information on the so-called pre-observational mean (POM). Results from a global circulation model for the Romanian area are incorporated in the discussion as well.     

Response prediction,experimental characterization and P‐spectra design of frames with viscoelastic–plastic dampers

Viscoelastic–plastic (VEP) dampers are hybrid passive damping devices that combine the advantages of viscoelastic and hysteretic damping. This paper first formulates a semi‐analytical procedure for predicting the peak response of nonlinear SDOF systems equipped with VEP dampers, which forms the basis for the generation of Performance Spectra that can then be used for direct performance assessment and optimization of VEP damped structures. This procedure is first verified against extensive nonlinear time‐history analyses based on a Kelvin viscoelastic model of the dampers, and then against a more advanced evolutionary model that is calibrated to characterization tests of VEP damper specimens built from commercially available viscoelastic damping devices, and an adjustable friction device. The results show that the proposed procedure is sufficiently accurate for predicting the response of VEP systems without iterative dynamic analysis for preliminary design purposes. A design method based on the Performance Spectra framework is then proposed for systems equipped with passive VEP dampers and is applied to enhance the seismic response of a six‐storey steel moment frame. The numerical simulation results on the damped structure confirm the use of the Performance Spectra as a convenient and accurate platform for the optimization of VEP systems, particularly during the initial design stage. Copyright © 2016 John Wiley & Sons, Ltd.     

Bi-normalized response spectra and seismic intensity in Bucharest for 1986 and 1990 Vrancea seismic events

The Vrancea subcrustal earthquakes of August 30,1986 and May 30,1990 are the two most recent seismic events that have occurred in Romania with moment magnitudes M W ≥ 6.9.The spectral analysis of the strong ground motions recorded in Bucharest reveals that despite small differences in magnitude between the 1986 and 1990 earthquakes,their frequency contents are very different,sometimes even opposing.The main focus of this study is to conduct a comparative analysis of the response spectra in terms of the bi-normalized response spectra(BNRS) proposed by Xu and Xie(2004 and 2007) for strong ground motions recorded in Bucharest during these two seismic events.The mean absolute acceleration and relative velocity response spectra for the two earthquakes are discussed and compared.Furthermore,the mean bi-normalized absolute acceleration and normalized relative velocity response spectra with respect to the control period T C are computed for the ground motions recorded in Bucharest in 1986 and 1990.The predominant period T P is also used in this study for the normalization of the spectral period axis.Subsequently,the methodology proposed by Martinez-Perreira and Bommer(1998) is applied in order to estimate the seismic intensity of the two events.The results are discussed and several conclusions regarding the possibility of using the bi-normalized response spectra(BNRS) are given.