Optimal seismic-resistant design of a planar steel frame

This paper illustrates the design of a four-storey, three-bay, moment-resisting, planar steel frame. Non-linear step-by-step integration is used as the analysis technique within the design process itself rather than as a check at the end of the design process. The method of design directly quantifies the accepted seismic-resistant design philosophy that a properly designed structure: (1) resists moderate ground motion without structural damage, and (2) resists severe ground motion without collapse. Actual ground motion accelerograms are selected and scaled to levels representing moderate and severe ground motions. Constraints quantifying structural damage and limited non-structural damage are constructed for the case of moderate ground motion, along with constraints quantifying collapse and limited structural damage for the case of severe ground motion. In addition serviceability constraints are imposed on structural behaviour under gravity loads only. Objective functions include the minimization of structural volume as well as the minimization of response quantities such as storey drifts and inelastically dissipated energy. A sophisticated optimization algorithm is utilized to solve the resulting mathematical programming problem. Comparative results concerning the computational phase as well as performance of both preliminary and final designs are presented. The practicality and reliability of the design method are assessed.     

TRANSALP—Cross-line recording during the seismic reflection transect in the Eastern Alps

Cross-line recording formed a companion experiment of the TRANSALP seismic reflection transect through the Eastern Alps, conducted by partner institutions from Austria, Germany and Italy in three field campaigns in the period fall 1998 to fall 1999. Besides of the originally expected three-dimensional control for the north–south running main transect, additional information on seismic anisotropy and alternative images of crucial parts of the main transect could be gained.Conventionally processed sections along N–S running common-midpoint (CMP) binning lines confirm and strengthen the predominance of midcrustal reflective structures of the ‘Sub-Tauern-Ramp’ beneath and south of the Tauern Window. Velocity analysis of the first arrivals exhibit about 10% higher velocities in east–west propagating P-waves, compatible with texture-dominated rock anisotropy, recorded on cross-lines at the Tauern Window. Pre-stack depth migration of cross-line recordings shows dominant south dip of the Sub-Tauern-Ramp with easterly dip components and a sub-horizontal root zone of the Sub-Dolomites-Ramp.     

Development of a numerical groundwater flow model using SRTM elevations

Remotely-sensed elevation data are potentially useful for constructing regional scale groundwater models, particularly in regions where ground-based data are poor or sparse. Surface-water elevations measured by the Shuttle Radar Topography Mission (SRTM) were used to develop a regional-groundwater flow model by assuming that frozen surface waters reflect local hydraulic head (or groundwater potential). Drainage lakes (fed primarily by surface water) are designated as boundary conditions and seepage lakes and isolated wetlands (fed primarily by groundwater) are used as observation points to calibrate a numerical flow model of the 900 km² study area in the Northern Highland Lakes Region of Wisconsin, USA. Elevation data were utilized in a geographic information system (GIS) based groundwater-modeling package that employs the analytic element method (AEM). Calibration statistics indicate that lakes and wetlands had similar influence on the parameter estimation, suggesting that wetlands might be used as observations where open water elevations are unreliable or not available. Open water elevations are often difficult to resolve in radar interferometry because unfrozen water does not return off-nadir radar signals.     

The millennium eruption of Hekla in February 2000

The 18th historic eruption of Hekla started on 26 February, 2000. It was a short-lived but intense event, emitting basaltic andesitic (55.5 wt% SiO₂) pyroclastic fragments and lava. During the course of the eruption, monitoring was done by both instruments and direct observations, together providing unique insight into the current activity of Hekla. During the 12-day eruption, a total of 0.189 km³ DRE of magma was emitted. The eruptive fissure split into five segments. The segments at the highest altitude were active during the first hours, while the segments at lower altitude continued throughout the eruption. The eruption started in a highly explosive manner giving rise to a Subplinian eruptive column and consequent basaltic pyroclastic flows fed by column collapses. After the explosive phase reached its maximum, the eruption went through three more phases, namely fire-fountaining, Strombolian bursts and lava effusion. In this paper, we describe the course of events of the eruption of Hekla and the origin of its magma, and then show that the discharge rate can be linked to different style of eruptive activity, which are controlled by fissure geometry. We also show that the eruption phases observed at Hekla can be linked with inferred magma chamber overpressure prior to the eruption.     

An Examination of the Atmospheric Chemistry of Mercury Using 210Pb and 7Be

Measurements of Hg (total gas-phase, precipitation-phase andparticulate-phase), aerosol mass, particulate ²¹⁰Pb and⁷Be and precipitation ²¹⁰Pb were made at an atmosphericcollection station located in a near remote area of northcentral Wisconsin,U.S.A. (46°10N, 89°50W) during the summers of 1993, 1994and 1995. Total Hg and ²¹⁰Pb were observed to correlate strongly(slope = 0.06 ± 0.03 ng mBq^-1; r ² =0.72) in rainwater. Mercury to ²¹⁰Pb ratios in particulate matter(0.03 ± 0.02 ng mBq^-1; r ² = 0.06) wereconsistent with the ratio in rain. Enrichment of the Hg/mass ratio (approx.5–50×) relative to soil and primary pollutant aerosols indicatedthat gas-to-particle conversion had taken place during transport. Comparisonof these results with models for the incorporation of Hg into precipitationindicates that atmospheric particles deliver more Hg to precipitation than canbe explained by the presence of soot. A lack of correlation between totalgas-phase Hg (TGM) and a ⁷Be/²¹⁰Pb function suggests novertical concentration gradient within the troposphere, and allows an estimateof TGM residence time of 1.5 ± 0.6 yr be made based on surface airsamples.     

Application of radium isotopes to determine crustal residence times of hydrothermal fluids from two sites on the Reykjanes Peninsula, Iceland

Radium isotopes were used to determine the crustal residence times of hydrothermal fluids from two geothermal wells (Svartsengi and Reykjanes) from the Reykjanes Peninsula, Iceland. The availability of rock samples from the subsurface (to depths of 2400 m) allowed direct comparison of the radium isotopic characteristics of the fluids with those of the rocks within the high temperature and pressure reaction zone. The ²²⁶Ra activity of the Svartsengi fluid was ∼one-fourth of the Reykjanes fluid and the ²²⁸Ra/²²⁶Ra ratio of the Svartsengi fluid was ∼twice that of Reykjanes. The fluid isotopic characteristics were relatively stable for both sites over the 6 years (2000-2006) of the study. It was determined, using a model that predicts the evolution of the fluid ²²⁸Ra/²²⁶Ra ratio with time, that both sites had fluid residence times, from the onset of high temperature water-rock reaction, of less than 5 years. Measurement of the short-lived ²²⁴Ra and ²²³Ra allowed estimation of the recoil input parameter used in the model. The derived timescale is consistent with results from similar studies of fluids from submarine systems, and has implications for the use of terrestrial systems in Iceland as an exploited energy resource.     

Incorporating nonlinear isotherms into robust multilayer sorptive barrier design

Sorptive barrier technologies have emerged as useful tools for addressing a wide range of remediation problems. When simulating barrier performance, numerous isotherm expressions are available for relating aqueous and sorbed concentrations. However, isotherm selection is non-trivial because alternative expressions may yield comparable fits to experimental data. Additionally, concentration data collected for parameter fitting is often outside the range of concentrations relevant to simulating barrier performance. This incompatibility necessitates extrapolation of isotherm behavior during simulation–optimization. Consequently, equally plausible isotherms may predict significantly different barrier performance.Numerical experiments involving organic contaminants were performed to examine the influence of isotherm selection and extrapolation on optimal barrier design. Ten isotherms were calibrated to existing experimental data and evaluated using information-theoretic selection criteria. When incorporated into simulation–optimization, extrapolation effects were clearly evident and optimal designs varied according to the chosen isotherm. To ensure robust barrier design in the presence of such variability, a simple methodology is proposed that utilizes a piecewise-minimum isotherm concept. By favoring plausible isotherms that predict the least amount of sorption, the methodology encourages conservative barrier design while respecting available data.