The role of overstrength on the seismic performance of asymmetric-plan structures

Uneven distribution of seismic demand in asymmetric-plan structures is a critical concern in earthquake-resistant design. Contemporary seismic design strategies that are based on linear elastic response, single load reduction factor, and uniform ductility demand throughout an asymmetric system generally lead to unsatisfactory performance in terms of realized ductilities and nonuniform damage distribution due to strong torsional coupling associated with asymmetric-plan systems. In many cases, actual nonlinear behavior of the structure displays significant deviation from what is estimated by a linear elastic, force-based seismic design approach. This study investigates the prediction of seismic demand distribution among structural members of a single-story, torsionally stiff asymmetric-plan system. The focus is on the effect of inherent unbalanced overstrength, resulting from current force-based design practices, on the seismic response of code-designed single-story asymmetric structures. The results obtained are utilized to compile unsymmetrical response spectra and uniform ductility spectra, which are proposed as assessment and preliminary design tools for estimating the seismic performance of multistory asymmetric structures. A simple design strategy is further suggested for improving the inelastic torsional performance of asymmetric systems. Providing additional strength to stiff edge members over their nominal design strength demands leads to a more balanced ductility distribution. Finally, seismic responses of several asymmetric case study structures designed with the aid of the proposed strategy are assessed for validating their improved performance.     

Generalized force vectors for multi‐mode pushover analysis of torsionally coupled systems

A generalized multi‐mode pushover analysis procedure was developed for estimating the maximum inelastic seismic response of symmetrical plan structures under earthquake ground excitations. Pushover analyses are conducted with story‐specific generalized force vectors in this procedure, with contributions from all effective modes. Generalized pushover analysis procedure is extended to three‐dimensional torsionally coupled systems in the presented study. Generalized force distributions are expressed as the combination of modal forces to simulate the instantaneous force distribution acting on the system when the interstory drift at a story reaches its maximum value during seismic response. Modal contributions to the generalized force vectors are calculated by a modal scaling rule, which is based on the complete quadratic combination. Generalized forces are applied to the mass centers of each story incrementally for producing nonlinear static response. Maximum response quantities are obtained when the individual frames attain their own target interstory drift values in each story. The developed procedure is tested on an eight‐story frame under 15 ground motions, and assessed by comparing the results obtained from nonlinear time history analysis. The method is successful in predicting the torsionally coupled inelastic response of frames responding to large interstory drift demands. Copyright © 2014 John Wiley & Sons, Ltd.     

Geochemistry and Zircon U-Pb Dates of Felsic-Intermediate Members of the Late Cretaceous Yüksekova Arc Basin: Constraints on the Evolution of the Bitlis–Zagros Branch of Neotethys (Elazığ, E Turkey)

During the Late Cretaceous in the Eastern Mediterranean, the northern branch of the southern Neotethys was closed by multiple northward subductions. Of these, the most northerly located subduction created the Baskil continental arc at around 82–84 Ma. The more southerly and intra-oceanic subduction, on the other hand, produced an arc-basin system,the Yüksekova Complex, as early as the late Cenomanian–early Turonian. The abundant and relatively well-studied basaltic rocks of this complex were intruded by dykes, sills and small stocks of felsic–intermediate rocks, not previously studied in detail. The intrusives collected from five different localities in the Elaz?? region of eastern Turkey are all subalkaline, with low Nb/Y values. Most of them have been chemically classified as rhyodacites/dacites, whereas a small number appear to be andesites. In normal mid-ocean-ridge basalt(N-MORB)-normalised plots, the intrusives are characterised by relative enrichments in Th and La over Nb, Zr, Hf, Ti and high field strength elements(HREEs), indicating their derivation from a subduction-modified source. While their relatively high, positive εN d(i) values(+6.4 and +7.2) might suggest a depleted mantle source for their ultimate origin, somewhat radiogenic Pb values indicate a sedimentary contribution to the source of the rocks. The overall geochemical characteristics indicate their generation in an oceanic arc setting. The zircon U-Pb Laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) data obtained from five felsic-intermediate rock samples yielded intrusion dates of 80–88 Ma. This suggests that the Elaz?? oceanic arc-related intrusives are slightly younger than those of the Yüksekova arc-basin system, but coeval with the Baskil continental arc. However, the felsic–intermediate intrusives show different geochemical characteristics(oceanic arc-type, with a lack of crustal contamination)to those of the Baskil continental arc. This indicates that these two igneous systems are unrelated and likely developed in different tectonic settings. This, in turn, supports a geodynamic model in which the northern strand of the southern Neotethys was consumed by multiple northward subductions.     

Geochemical characteristics of ophiolitic rocks from the southern margin of the Sivas basin and their implications for the Inner Tauride Ocean,Central-Eastern Turkey

Number of dismembered ophiolite bodies crop out between Sivas and Malatya on the top of the Eastern Tauride platform in the central-eastern Turkey. One of which at the southern margin of the Sivas basin in the Tecer Mountain area comprises melange and the lower part of an oceanic lithospheric section on top of the Tauride platform. The mantle tectonites are characterized by variably serpentinized harzburgites and dunites, and are intruded by numerous isolated dykes. The gabbroic cumulates consist of olivine gabbro, gabbro and gabbronorite. The major and trace element geochemistry of the mafic cumulate rocks suggests that the primary magma was compositionally similar to those observed in modern island-arc tholeiitic sequences. The isolated dykes are exclusively basaltic in composition and display geochemically two distinct subgroups: Group I is represented by high TiO₂ (.87–1.47 wt.%) and other incompatible elements, whereas Group II is characterized by low TiO₂ (.36–.66 wt.%) and other incompatible elements. The Group I isolated diabase dykes have flat to slightly LREE-depleted profiles (La/Yb_N = .32–.79), whereas the Group II isolated diabase dykes are more depleted in general and have a LREE-depleted character (La/Yb_N = .19–.49). This suggests that the isolated dykes were derived from an island arc tholeiitic magma (Nb/Y = .02–.05) with different degrees of partial melting (Group II > Group I) and relatively high oxygen fugacity in intra-oceanic subduction zone. The ophiolitic rocks in the study area may well be compared with the Divri?i ophiolite to the southeast. All the evidence suggests that the isolated dykes in the Tecer Mountain area differ from the alkaline isolated dykes cutting the Divri?i ophiolite. Since the late stage dykes (~76 Ma) in the Divri?i area are alkaline, the tholeiitic isolated dykes in the present study should have been emplaced prior to the alkaline dykes during Late Cretaceous SSZ-spreading (~90 Ma) within the Inner Tauride Ocean.     

Barrier holes and trench application to reduce blast induced vibration in Seyitomer coal mine

In this research, experimental applications have been performed to reduce blast induced vibrations in open pit mines. For this purpose, artificial discontinuity zones such as barrier holes and trench were opened in a dragline panel of Seyitomer Lignite Enterprise, Kutahya, Turkey. Peak particle velocities in front of and behind them were measured by seismographs. In this way, their effect against vibration was observed and compared. Barrier holes were opened 24 m deep through 3 parallel lines and aligned at 1 m spacing. On the other hand, the trench had 8 m depth and 4 m width. During the research, 209 measurements were taken belonging to 105 explosions. Twenty-eight explosions were carried out in the barrier holes experiments and 77 explosions were carried out in the trench experiments. A decrease in vibration of 14.3–18.5% was obtained behind the barrier holes while a decrease of 24.8–58.1% was provided by the trench.     

Factors controlling stratal pattern and facies distribution of fluvio‐lacustrine sedimentation in the Sivas mini‐basins,Oligocene (Turkey)

The Sivas Basin, located in the Central Anatolian Plateau of Turkey, is a foreland basin that records a complex interaction between sedimentation, salt tectonics and regional shortening during the Oligo‐Miocene leading to the formation of numerous mini‐basins. The Oligocene sedimentary infill of the mini‐basins consists of a thick continental succession, the Karayün Formation, comprising a vertical succession of three main sub‐environments: (i) playa‐lake, (ii) fluvial braided, and (iii) saline lacustrine. These sub‐environments are seen as forming a large Distributive Fluvial System (DFS) modified through time as a function of sediment supply and accommodation related to regional changes in climate and tectonic regime. Within neighbouring mini‐basins and despite a similar vertical stratigraphic succession, subtle variations in facies assemblages and thickness are observed in stratigraphic units of equivalent age, thus demonstrating the local control exerted by halokinesis. Stratigraphic and stratal patterns reveal in great detail the complex interaction between salt tectonics and sedimentation including different types of halokinetic structures such as hooks, wedges and halokinetic folds. The regional variations of accommodation/sediment supply led to coeval changes in the architectural patterns recorded in the mini‐basins. The type of accommodation regime produces several changes in the sedimentary record: (i) a regime dominated by regional accommodation limits the impact of halokinesis, which is recorded as very small variations in stratigraphic thickness and facies distribution within and between mini‐basins; (ii) a regime dominated by localized salt‐induced accommodation linked to the subsidence of each individual mini‐basin enhances the facies heterogeneity within the DFS, causing sharp changes in stratigraphic thickness and facies assemblages within and between mini‐basins.     

An adaptive Markov chain algorithm applied over map-matching of vehicle trip GPS data

Markov chains have frequently been applied to match the probable routes with a set of GPS trip data that a pilot vehicle is emitting over a specific graph road network. This class of map- matching (MM) algorithms presently demonstrates and involve statistical and ad-hoc measures to drive the Markov chain transitional probabilities in picking the best route combinations constrained over the graph road network. In this study, we have devised an adaptive scheme to modify the Markov Chain (MC) kernel window as we move along the GPS samples to reduce the mistakes that can happen by the use of narrower MC widths. The measure for temporarily increasing the MC window width is chosen to be the ratio between the geodesic distance of current route to the actual geodesic distance between each pair of GPS samples. This adaptive use of MC has shown to have hardened the results significantly with tolerable computational cost increase. The details of the overall algorithm are depicted by the example routes extracted from various vehicle trips and the results are shown to validate the usefulness of the algorithm in practice.