Critical response of structures to multicomponent earthquake excitation

This paper aims to develop an improved understanding of the critical response of structures to multicomponent seismic motion characterized by three uncorrelated components that are defined along its principal axes: two horizontal and the vertical component. An explicit formula, convenient for code applications, has been derived to calculate the critical value of structural response to the two principal horizontal components acting along any incident angle with respect to the structural axes, and the vertical component of ground motion. The critical response is defined as the largest value of response for all possible incident angles. The ratio r_cr/r_srss between the critical value of response and the SRSS response—corresponding to the principal components of ground acceleration applied along the structure axes—is shown to depend on three dimensionless parameters: the spectrum intensity ratio γ between the two principal components of horizontal ground motion characterized by design spectra A(T_n) and γA(T_n); the correlation coefficient α of responses r_x and r_y due to design spectrum A(T_n) applied in the x‐ and y‐directions, respectively; and β = r_y/r_x. It is demonstrated that the ratio r_cr/r_srss is bounded by 1 and . Thus the largest value of the ratio is , 1.26, 1.13 and 1.08 for γ = 0, 0.5, 0.75 and 0.85, respectively. This implies that the critical response never exceeds times the result of the SRSS analysis, and this ratio is about 1.13 for typical values of γ, say 0.75. The correlation coefficient α depends on the structural properties but is always bounded between −1 and 1. For a fixed value of γ, the ratio r_cr/r_srss is largest if β = 1 and α = ±1. The parametric variations presented for one‐storey buildings indicate that this condition can be satisfied by axial forces in columns of symmetric‐plan buildings or can be approximated by lateral displacements in resisting elements of unsymmetrical‐plan buildings. Copyright © 2000 John Wiley & Sons, Ltd.     

Assessment of phosphogypsum impact on the salt-marshes of the Tinto river (SW Spain): role of natural attenuation processes

About 120 Mton of phosphogypsum from the fertiliser industry were stack-piled on the salt-marshes of the Tinto river (Spain). This paper investigates the capacity of salt-marshes to attenuate contamination due to downward leaching from phosphogypsum. Solids and pore-waters were characterized at different depths of the pile to reach the marsh-ground. In superficial zones, metals were highly mobile, and no reduced sulphur was found. However, pollutant concentration decreased in the pore-water in deeper oxygen-restricted zones. Metal removal occurred by precipitation of newly formed sulphides, being this process main responsible for the contamination attenuation. Pyrite-S was the main sulphide component (up to 2528 mg/kg) and occurred as framboids, leading to high degrees of pyritization (up to 97%). The sulphidization reaction is Fe-limited; however, excess of acid-volatile sulphide over other metals cause precipitation of other sulphides, mainly of Cu and As. This decrease in metal mobility significantly minimises the impact of phosphogypsums on the salt-marshes.     

Cenomanian events in the deep western Basque Basin: the Leioa section

Analysis of the microfaunas (foraminifera, ostracods) and the stable isotope values (δ¹³C, δ¹⁸O) of the Leioa section, as representative of the deep Basque Basin, has allowed us to propose a detailed palaeoenvironmental reconstruction of this region during the Cenomanian, as well as to register global chronostratigraphic reference levels to facilitate interregional correlations. During the Cenomanian, part of the basin, the Plentzia Trough, was occupied by intermediate water masses, as deduced by the relative percentages of planktonic (Rotalipora) and benthonic foraminifera. A noticeable change is observed at the middle-late Cenomanian transition: the replacement of the dominance of keeled (rota-liporids) by incipiently-keeled (dicarinellids, praeglobotruncanids) planktonic foraminifera, indicative of the new influence of the upper intermediate waters. The temporary effect of shallow waters is deduced in one interval of the latest early Cenomanian and two more of the middle Cenomanian, as indicated by the dominance of globular planktonic foraminifera (hedbergellids). These water masses were moderately to strongly hypoxic (<4 to <2 ml/l of disolved oxygen) after the ostracod platycopid signal and benthonic foraminiferal hypoxic indicators. The dysaerobia may have been particulary strong (almost anoxia?) during part of the middle Cenomanian. Micronutrient availability was also restricted during several intervals of the middle Cenomanian, as indicated by the sudden decrease in the species diversity of the calcitic benthonics during the period when increased trends of the δ¹³C isotopic signals are observed. The combination of both hypoxia and nutrient depletion produced drastic changes in the microfaunal assemblages, with emigrations and local extinctions, showing benthonic perturbations from the time indicated by the base of theRotalipora reicheliZone onwards. From the beginning until the end of the middle Cenomanian, eleven of these perturbations are recorded as regional bioevents, using as bioevent-markers, intervals where microfauna was absent (including benthic-free intervals, B-FI; benthonic calcitic-free intervals, BC-FI; and ostracod-free intervals, O-FI). These changes led to the renewal of the microfaunas; benthonic foraminifera renewed their specific stocks during the early to early middle Cenomanian, with planktonic foraminifera and ostracods undergoing renewal at the end of the middle Cenomanian. Isotope values of δ¹⁸O and δ¹³C are consistent with the palaeoenvironmental changes detected by the microfaunas; their maximum and minimum shifts coincide with the bioevents. The double-peaked positive shift of δ¹³C for the mid-Cenomanian of northwest Europe (Jenkynset al., 1994; Paulet al., 1994a) has been recognized in this series of the Basque Basin. The palaeoenvironmental perturbations deduced in the Cenomanian of the Leioa section are attributed essentially to palaeoceanographic changes, where intermediate water masses profoundly influenced the planktonic and benthonic ecosystems. The influence of other local causes, such as volcanic activity at that time, or tectonics between the Iberian and European plates, are more difficult to prove. Several of the bioevents defined in the middle Cenomanian of this basin could probably be global in nature, and thus may be useful for establishing interregional correlations.     

Diet selection in captivity by a generalist herbivorous rodent (Octodon degus) from the Chilean coastal desert

Five captive adult female degus (Octodon degus) were offered leaves and twigs to eat from three woody (Adesmia bedwellii,Porlieria chilensisandProustia pungens) and two suffruticose (Baccharis paniculataandChenopodium petiolase) shrubs that provide cover in their natural habitat. The degus discriminated among the plant species, consuming lower amounts ofP. chilensis. Daily body mass losses of degus were significantly higher when they were fed uponP. pungensandP. chilensis. The nutritional value of plants, concomitant with degu nutritional requirements, may explain changes in shrub cover previously found to follow removal of degus from experimental plots.     

Vegetation in an altitudinal gradient along the R?́o Loa in the Atacama Desert of northern Chile

Six sites between 0 m and 4000 m were sampled for plant and soil chemical characteristics along the Río Loa, Atacama Desert, Chile. Sites located between 0 m and 1500 m showed lower species richness, higher plant cover and higher herbaceous productivity than the upper part of the altitudinal gradient. The number of species varied non-linerly with precipitation along the altitudinal gradient. Plant cover and herbaceous productivity in the lowlands is characterized by thePluchea absinthioides Distichlis spicataassociation of anthropic origin. We propose that vegetation structure along the altitudinal gradient has been affected by past and present human activities, and climatic and edaphic factors.     

X-Ray and optical observations of the X-ray source EX0020528+1454.8

We present preliminary results of the EXOSAT X-ray observations and quasisimultaneous and simultaneous optical photometry of the X-ray source EX0020528+1454.8=1E0205+149 found independently as an serendipitous source both with Einstein and EXOSAT satellites. The optical counterpart is a pair of dMe stars. Our results indicate that the object is variable both in X-rays and optical wavelenghts, and probably belongs to dMe flare stars.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Fishery development — the Latin American model

Ten years ago, the Food and Agriculture Organization (FAO) and the Inter-American Development Bank undertook an analysis of the possibilities and significance of fishery development in Latin America, formulating guidelines for action to promote development and outlining strategies and means for implementation. This report describes the evolution of fishery development in the Latin American region over the past decade.     

Reduction of jack-up and crane vessel resistance and bow swamping

A large bow wave forms when blunt-shaped vessels like self-propelled jack-up crane vessels (liftboats) operate at high speeds. Above a critical speed, this bow wave spills over the bow causing swamping. To investigate this phenomena, towing tank tests of a 1/25 scale model liftboat hull were done over a speed range of 3–8 kn. The test showed above 4 kn the bow wave formed and the vessel trimmed by the bow. At speeds above 8 kn the bow wave spilled over the bow (swamping). To cancel this critical bow wave a vertical bow plate was fitted ahead of the liftboat bow. This bow plate reduced the bow wave formation and achieved a 10–15% reduction in the towing resistance. The wave cancellation bow plate can reduce the liftboat power or increase its liftboat speed and operating range.