Probabilistic economic seismic loss estimation in steel buildings using post‐tensioned moment‐resisting frames and viscous dampers

The potential of post‐tensioned self‐centering moment‐resisting frames (SC‐MRFs) and viscous dampers to reduce the economic seismic losses in steel buildings is evaluated. The evaluation is based on a prototype steel building designed using four different seismic‐resistant frames: (i) conventional moment resisting frames (MRFs); (ii) MRFs with viscous dampers; (iii) SC‐MRFs; or (iv) SC‐MRFs with viscous dampers. All frames are designed according to Eurocode 8 and have the same column/beam cross sections and similar periods of vibration. Viscous dampers are designed to reduce the peak story drift under the design basis earthquake (DBE) from 1.8% to 1.2%. Losses are estimated by developing vulnerability functions according to the FEMA P‐58 methodology, which considers uncertainties in earthquake ground motion, structural response, and repair costs. Both the probability of collapse and the probability of demolition because of excessive residual story drifts are taken into account. Incremental dynamic analyses are conducted using models capable to simulate all limit states up to collapse. A parametric study on the effect of the residual story drift threshold beyond which is less expensive to rebuild a structure than to repair is also conducted. It is shown that viscous dampers are more effective than post‐tensioning for seismic intensities equal or lower than the maximum considered earthquake (MCE). Post‐tensioning is effective in reducing repair costs only for seismic intensities higher than the DBE. The paper also highlights the effectiveness of combining post‐tensioning and supplemental viscous damping by showing that the SC‐MRF with viscous dampers achieves significant repair cost reductions compared to the conventional MRF. Copyright © 2016 John Wiley & Sons, Ltd.     

A Study of Fog Characteristics Using a Coupled WRF–COBEL Model Over Thessaloniki Airport, Greece

An attempt is made to couple the one dimensional COBEL-ISBA (Code de Brouillard à l’échelle Locale-Interactions Soil Biosphere Atmosphere) model with the WRF (Weather Research and Forecasting)–ARW (Advanced Research WRF) numerical weather prediction model to study a fog event that formed on 20 January 2008 over Thessaloniki Airport, Greece. It is the first time that the coupling of COBEL and WRF models is achieved and applied to a fog event over an airport. At first, the performance of the integrated WRF–COBEL system is investigated, by validating it against the available surface observations. The temperature and humidity vertical profiles were used for initializing the model. The performance of WRF–COBEL is considered successful, since it realistically simulated the fog onset and dissipation better than the WRF alone. The COBEL’s sensitivity to initial conditions such as temperature and specific humidity perturbations was also tested. It is found that a small increase of temperature (~1°C) counteracts fog development and results in less fog density. On the other hand, a small decrease of temperature results in much denser fog formation. It is concluded that the integrated model approach for aviation applications can be useful to study fog impact on local traffic and aviation.     

Volume integrals of the products of spherical harmonics and their application to viscous dissipation phenomena in fluids

The equations governing the conversion of kinetic energy into heat in moving viscous media are formulated as volume integrals of products of spherical harmonics. Although the formulation of the fundamental equations is classical, difficulties in the integration of certain products of generalized spherical harmonics over a sphere have permitted heretofore the treatment of only two cases. The closed, form evaluation of eight fundamental types of definite integrals of the product of spherical harmonics, some of them new, or at least missing in the literature, makes possible for the first time the evaluation of these volume integrals in closed form for arbitrary order and index. Explicit details are given for the rates of energy dissipation produced by viscous motions characterized by spheroidal as well as toroidal symmetry.     

Stratigraphy of the mid-Holocene black bands in Lakes Michigan and Huron: Evidence for possible basin-wide anoxia

The post-glacial history of the Great Lakes has involved several changes in lake levels throughout the latest Pleistocene and Holocene, resulting from the changing position of the retreating Laurentide ice sheet, outlet incision and isostatic rebound. The final lowering of lake levels occurred at approximately 7600 ¹⁴C yr BP, after which lake levels began to rise again to the Nipissing highstand at approximately 4700 ¹⁴C yr BP. During this time of rising lake levels, black bands of iron sulfide were being formed in the sediments of all five of the Great Lakes. These bands signify suboxic to anoxic conditions, at least within the sediments and possibly at the sediment-water interface, during the middle Holocene warm interval. During this interval, the climate was warmer and drier than present, possibly resulting in the occasional absence of seasonal turnover in the lakes. We examined a series of piston cores from northern Lakes Michigan and Huron and found that the black bands are correlatable among cores taken from within the same basin. The observation that the banding can be correlated suggests a basin-wide cause, near-bottom or sub-bottom anoxia in the northern Michigan and northern Huron sediments during the mid-Holocene warm period. The sedimentary and geochemical processes in the Great Lakes during the middle Holocene warm interval are good indicators of possible future scenarios for the lakes as a result of global warming, as 21^st-century temperatures are predicted to reach similar levels due to increased concentrations of greenhouse gases.     

The dynamics of conservative mixing in estuaries

Mixing plots, in which a dissolved constituent is plotted against salinity or chlorinity, are commonly used to interpret conservative and non-conservative processes in estuarine systems. A bend in the resulting curve is generally interpreted as indicative of the reactive or non-conservative nature of the constituent or the presence of multiple sources or sinks within the estuary. This paper demonstrates analytically that bends in mixing curves may also result from temporal variations in end-member (river or ocean) constituent concentrations even for conservative constituents. A one-dimensional dispersion equation is used to calculate the distribution of salinity and a conservative constituent in a model estuary. Both straight and bent mixing curves are shown resulting simply from changing the variability of the river constituent concentration. For no variability the curve is straight. For variability with a period much less than the flushing time, the average curve for a general data set straight, whereas the curve for a synoptic data set is bent. For variability with a period greater than the flushing time a bent curve results. Since bent mixing curves can occur for conservative properties, the use of these curves for interpretation of estuarine processes must be undertaken with an understanding of the temporal variability of the river and ocean constituents and their relationship to the estuary mixing properties and flushing time.     

Evidence for extensive diagenesis,Madagascar Basin,Deep Sea Drilling Site 245

Deep Sea Drilling Hole 245 (31°32′S, 52° 18′E) in the southwest Indian Ocean shows pronounced linear concentration-depth gradients in interstitial dissolved Ca, Mg and Sr. Electrical conductivity tests enable us to make the estimate of a constant diffusion coefficient with depth of about 2 × 10^?6 cm²/sec. The shapes of the concentration-depth gradients suggest that the major reaction sites in this hole are situated in the basal sediments and/or underlying basalts. It is proposed that observed interstitial water concentration changes in Ca and Mg are related to alteration of basaltic material, whereas those in Sr are due to calcium carbonate recrystallization processes. Support for the basaltic material alteration hypothesis comes from petrochemical and mineralogical data. Geochemical data also indicate that the high contents in Fe and Mn of the basal sediments can be related to low temperature alteration of basaltic glass and not necessarily to ‘hydrothermal’ activity.     

Drainage basins as process-response systems: An example from Central Macedonia,North Greece

Study of two subareas of the same large basin in North Greece determined that differences in processes and form exist between the two subareas. These differences were brought on by man's interference upon one of the subareas. In area A, seminatural vegetation promotes throughflow and protects the surface from overland flow. Hence, natural erosion takes place primarily by channel deepening and infall of side slopes into the channels. In area B, clearing of the seminatural vegetation and the improper ploughing for cultivation increases the overland flow which promotes slope erosion but the augmented debris supply has checked channel erosion. These processes change the form of the drainage basins of the area.     

An error analysis of profile flux,stability, and roughness length measurements made in the marine atmospheric surface layer

An analytical error analysis of profile-derived fluxes of heat, moisture, and momentum, along with stability and roughness length, is performed using the accuracies of the constituent temperature, humidity, and wind speed measurements. Five experiments, representing more than two thirds of the existing marine profile data presently contained in the literature, are compared. Much of the profile data examined was used to develop the transfer coefficients presently employed by a large number of competing bulk aerodynamic flux schemes. Depending upon the experiment, typical profile-method measurement errors were found to range from 15 to 35% for a sensible heat flux of ± 10 W m^-2, from 15 to 105% for a latent heat flux of ± 100 W m^-2, from 10 to 40% for a stress of 0.05 N m^-2, from 15 to 60% for a Monin-Obukhov stability of ± 0.05, and from 25 to 100% for a roughness length of 2 × 10^-4 m. Smaller magnitude flux values were found to contain typical errors as large as 100% for sensible heat flux, 300% for latent heat flux, and 60% for stress.