Modern sands derived from the Vertiskos Unit of the Serbomacedonian Massif (N. Greece): a preliminary study on the weathering of the Unit

Modern sand samples were collected from the Vertiskos Unit of the Serbomacedonian Massif, northern Greece, and were examined for their texture and mineralogical composition. They were collected from active channels and torrents. The textural study demonstrated that these modern sands are moderately to very-poorly sorted, often polymodal in grain size distribution, texturally and mineralogically immature to submature, and consist of coarse-grained gravelly sands to slightly-gravelly muddy sands. The dominant composition is quartzofeldspathic. All samples contain detrital minerals of metamorphic origin, mainly amphibole and garnet, in addition to minor amounts of pyroxene and detrital calcite. These sediments were deposited rapidly and close to their source, the metamorphic basement of the Vertiskos Unit. The mineral constituents of the samples indicate that the Vertiskos Unit is undergoing rapid physical weathering due to the temperate and seasonal climate. The results of this study suggest that these modern sands constitute one sedimentary petrologic province comprised of primarily of amphibole-garnet.     

Sectional forces for seismic design of R/C frames by linear time history analysis and application to 3D single-story buildings

The aim of the present paper is to present a rational procedure for the appropriate selection of the sectional forces needed for the calculation of the longitudinal reinforcement to R/C elements within the context of linear time history analysis. The proposed procedure is based on the maximum normal stresses, which occurs in each relevant cross section, and takes into consideration the critical angle of the seismic excitation, i.e., the angle that yields the maximum value of each response quantity of interest. Moreover, in an attempt to realistically interpret pertinent code provisions, three other code compatible methods of selecting the cross sectional forces are presented and compared to the here proposed method. For this purpose, three single-story buildings subjected to 47 bi-directional strong earthquake ground motions are analyzed. For each ground motion, the longitudinal reinforcement at all critical cross sections is calculated using the above four methods. Furthermore, the necessary reinforcement due to 3 and 7 representative earthquake records, required by the seismic code provisions, is determined. Comparison of results clearly shows that methods compatible with current seismic code provisions can significantly underestimate the necessary reinforcement with regards to the proposed method.     

An overview of seismic testing needs in Europe: towards a new advanced experimental facility

This paper presents a synthesis of the activities carried out in the framework of the European project EFAST (design study of a European Facility for Advanced Seismic Testing) to determine the general characteristics of a new European world-class facility for earthquake testing of structures. To this end the demands for the necessary testing to support the modern seismic engineering research have been investigated and compared to the actual capabilities of European laboratories. The outcome is the determination of performance objectives and requirements in the gross. On the basis of the needs assessment carried out during the first phase of the project and taking into account the technological advances in both experimental techniques and equipment (hardware and software) for seismic testing, a modern facility for experimental seismic research should be composed, mainly, of a high performance shaking tables array and a large reaction structure where both traditional (pseudo-static/dynamic) and innovative testing techniques (e.g. real time hybrid testing) can be applied and combined. A tentative layout of the facility is also proposed and issues related to the best utilization of such a laboratory are discussed.     

Petrographic Investigation of Microcrack Initiation in Mafic Ophiolitic Rocks Under Uniaxial Compression

This paper investigates the influence of the petrographic characteristics of mafic ophiolitic rocks on the initiation and propagation of microcracks during uniaxial compression. The microcrack patterns of a troctolite and a diorite, collected from the Pindos and Othrys ophiolites (Greece), respectively, were analysed. Thorough observation and quantification of microcracks before and after the uniaxial compression test were conducted. Combined fluorescent and polarised microscopy of polished thin sections, together with digital image analysis, indicated that the intragranular microcracks are the dominating crack type in both loaded and unloaded specimens, only in terms of their total number and length. On the other hand, the intergranular and transgranular cracks seem to grow more readily compared to the intragranular cracks, implying that the longer microcracks grow more extensively under stress. The orientation of most of the newly formed intragranular and transgranular microcracks is nearly parallel to the loading direction; however, some of the randomly oriented transgranular cracks have probably been formed during the propagation of intergranular cracks. In the troctolite, the frequency of the intragranular microcracks decreases in the olivine crystals after the uniaxial compression test due to their partial serpentinisation, which increases their resistance to brittle deformation. In the plagioclase crystals of the troctolite, microcracks are often oriented parallel to the cleavage planes, implying that such crystallographic orientations act as planes of weakness. On the contrary, the plagioclase crystals of the diorite are mainly crossed by randomly oriented microcracks, presumably due to their high degree of alteration. In the diorite, the evolution of microcracks is substantially controlled by the two perfect cleavages of amphibole. The failure of a rock occurs as a result of the growth, interaction and coalescence of a great number of pre-existing and newly formed intragranular and transgranular microcracks. The petrographic and microcrack analysis may assist in the selection of the most suitable rock type for various construction applications.     

Sediment characteristics and water physicochemical parameters of the Lysimachia Lake, Western Greece

In the present paper, we present the sedimentological characteristics and the water physicochemical parameters of Lysimachia Lake, which is one of the most important lakes of Western Greece, as it is protected by international conventions and is listed in the Natura 2000 European Network. Sedimentological analysis involved grain size analyses, moment measures, total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) measurements, as well as determination of the clay minerals content. Water physicochemical parameters such as pH, temperature, conductivity and dissolved oxygen were measured in situ with portable equipment, while nutrients such as nitrates, nitrites, phosphates and ammonium ions, as well as TOC and TN were analyzed in a time period of 1 year seasonal monitoring. Geographical distribution of grain size and geochemical parameters indicated a clear partition in the northern and southern parts of the lake. This phenomenon can related to the discharging of a channel into the lake, the discharging of sewage effluents from Agrinio city during the last years as well as the type of clay minerals distribution. Clay minerals analyses indicated that smectite predominates in the northern part of the lake, whereas chlorite is more abundant in the southern parts. This explain the higher amounts of TOC and TN observed in the northern part of the lake and can be correlated with the higher external surface and adsorption capacity of minerals in the smectite-rich sediments. The four seasons monitoring of water physicochemical parameters indicates a relatively higher values of TOC and TN in the northern part of the lake, while nutrient concentrations indicate a uniform geographical distribution along the lake.     

Effects in the anomalistic period of celestial bodies due to a logarithmic correction to the Newtonian gravitational potential

We study the motion of a secondary celestial body under the influence of the logarithmic corrected gravitational force of a primary one. This kind of correction was introduced by Fabris and Campos (Gen. Relativ. Gravit. 41(1):93, 2009). We derive two equations to compute the rate of change of the anomalistic period with respect to the eccentric anomaly and its total variation over one revolution. In a kinematical sense, this influence produces an apsidal motion. We perform numerical estimations for some celestial bodies. We also compare our results to those obtained by considering a Yukawa correction.     

Behaviour of deep immersed tunnel under combined normal fault rupture deformation and subsequent seismic shaking

Immersed tunnels are particularly sensitive to tensile and compressive deformations such as those imposed by a normal seismogenic fault rupturing underneath, and those generated by the dynamic response due to seismic waves. The paper investigates the response of a future 70 m deep immersed tunnel to the consecutive action of a major normal fault rupturing in an earthquake occurring in the basement rock underneath the tunnel, and a subsequent strong excitation from a different large-magnitude seismic event that may occur years later. Non-linear finite elements model the quasi-static fault rupture propagation through the thick soil deposit overlying the bedrock and the ensuing interaction of the rupture with the immersed tunnel. It is shown that despite imposed bedrock offset of 2 m, net tension or excessive compression between tunnel segments could be avoided with a suitable design of the joint gaskets. Then, the already deformed (“injured”) structure is subjected to strong asynchronous seismic shaking. The thick-walled tunnel is modelled as a 3-D massive flexural beam connected to the soil through properly-calibrated nonlinear interaction springs and dashpots, the supports of which are subjected to the free-field acceleration time histories. The latter, obtained with 1-D wave propagation analysis, are then modified to account for wave passage effects. The joints between tunnel segments are modeled with special non-linear hyper-elastic elements, properly accounting for their 7-bar longitudinal hydrostatic pre-stressing. Sliding is captured with special gap elements. The effect of segment length and joint properties is explored parametrically. A fascinating conclusion emerges in all analysed cases for the joints between segments that were differentially deformed after the quasi-static fault rupture: upon subsequent very strong seismic shaking, overstressed joints de-compress and understressed joints re-compress—a “healing” process that leads to a more uniform deformation profile along the tunnel. This is particularly beneficial for the precariously de-compressed joint gaskets. Hence, the safety of the immersed tunnel improves with “subsequent” strong seismic shaking!     

A new definition of strong motion duration and related parameters affecting the response of medium–long period structures

This study presents a new definition of the strong motion duration combining the alternative bracketed and significant duration definitions. Based on the time integral of the absolute ground velocity, a new index is defined, as cumulative absolute displacement (CAD), and used to estimate the strong motion duration. The proposed bracketed-significant duration t_bs is found to be well correlated with the strong motion part of the records, especially in the case of near-source events. The duration t_bs and the CAD index are used to assess the anticipated structural behavior of medium–long period structures.     

Seismic fragility curves for greek bridges: methodology and case studies

This study focusses on the estimation of seismic fragility curves for all common bridge types found in modern greek motorways. At first a classification scheme is developed in order to classify the existing bridges into a sufficient number of classes. A total of 11 representative bridge classes resulted, based on the type of piers, deck, and pier-to-deck connection. Then an analytical methodology for deriving fragility curves is proposed and applied to the representative bridge models. This procedure is based on pushover analysis of the entire bridge and definition of damage states in terms of parameters of the bridge pushover curves. The procedure differentiates the way of defining damage according to the seismic energy dissipation mechanism in each bridge, i.e. bridges with yielding piers of the column type and bridges with bearings (with or without seismic links) and non-yielding piers of the wall type. The activation of the abutment-backfill system due to closure of the gap between the deck and the abutments is also taken into account. The derived fragility curves are subjected to a first calibration against empirical curves based on damage data from the US and Japan.     

Investigating dynamic coupling in geospace through the combined use of modeling,simulations and data analysis

Comprehensive understanding of the dynamics of the coupled solar wind-magnetosphere-ionosphere system is of utmost interest, both from the perspective of solar system astrophysics and geophysics research and from the perspective of space applications. The physical processes involved in the dynamical evolution of this complex coupled system are pertinent not only for the Sun-Earth connection, but also for major phenomena in other astrophysical systems. Furthermore, the conditions in geospace collectively termed space weather affect the ever increasing technological assets of mankind in space and therefore need to be understood, quantified and efficiently forecasted. The present collaborative paper communicates recent advances in geospace dynamic coupling research through modeling, simulations and data analysis and discusses future directions.