Distribution by Scientific Domains

Kinds of Beam

  • cantilever beam
  • composite beam
  • concrete beam
  • cone beam
  • curved beam
  • elastic beam
  • electron beam
  • flexible beam
  • focused ion beam
  • focused laser beam
  • incident beam
  • ion beam
  • laser beam
  • molecular beam
  • monochromatic beam
  • proton beam
  • sandwich beam
  • steel beam
  • synchrotron beam
  • thin beam
  • timoshenko beam
  • ultrasound beam
  • x-ray beam

  • Terms modified by Beam

  • beam diameter
  • beam direction
  • beam element
  • beam energy
  • beam epitaxy
  • beam irradiation
  • beam lithography
  • beam model
  • beam profile
  • beam propagation method
  • beam quality
  • beam radiation
  • beam radiation therapy
  • beam radiotherapy
  • beam reflectance measurement
  • beam rt
  • beam size
  • beam structure
  • beam system
  • beam theory
  • beam therapy
  • beam tomography

  • Selected Abstracts

    BEAM , Geoelectrical Ahead Monitoring for TBM-Drives

    Arnim Kaus Dr. rer.nat.
    BEAM is a non-intrusive focused-electrical induced polarisation ground prediction technique, permanently operating while TBM tunnelling. Main components of the survey system are the measuring unit placed in the TBM operator cabin and special adapted excavation tools which are used as electrodes. The unit is connected to the guidance system and receives the boring signal which allows fully automatic data acquisition and visualisation in real-time on an integrated monitor. Communication facilities transfer the forecast results to every accredited computer world wide simultaneously. Based on the measuring data the percentage frequency effect PFE and the resistivity R, an advanced evaluation software is established for geoelectrical-geological/hydrogeological classification and interpretation. Selected case studies from international TBM projects are outlined with prediction results of different kinds of exploration targets and geological situations. Since 2000 the geophysical probing system is fulfilling the practical demands under the rough and various conditions of TBM tunnelling work by indicating reliable results in hard rock as well as in soft ground. BEAM , Geoelektrische Vorauserkundung für TBM-Vortriebe BEAM ist eine zerstörungsfreie, vortriebsbegleitende Baugrund-Vorauserkundungs-Technologie auf Basis der fokussierend-elektrischen induzierten Polarisation. Das Monitoring-System besteht hauptsächlich aus einem Messgerät, das in der Steuerkabine aufgestellt werden kann, und aus speziell angepassten, bauseits vorhandenen Abbauwerkzeugen und Sicherungsmitteln, die als Elektroden dienen. Die Messeinheit wird mit dem bestehenden Vermessungssystem verbunden und empfängt das Bohrsignal, sodass vollautomatisierte Messungen durchgeführt werden, ohne die Tunnelvortriebsarbeiten zu stören, bei gleichzeitiger Datenauswertung und Visualisierung der Ergebnisse in Echtzeit auf dem integrierten Bildschirm der Einheit. Durch Anschluss an die Kommunikationseinrichtungen der Baustelle lassen sich die Vorauserkundungsdaten zeitgleich an jeden akkreditierten Computer weltweit transferieren. Eine innovative Auswertesoftware bewerkstelligt die geoelektrisch-geologische/hydrogeologische Klassifikation und Interpretation, die auf den Messparametern Prozent Frequenz Effekt PFE und dem Widerstand R basiert. Ausgewählte Fallbeispiele aus internationalen TBM-Projekten zeigen Vorauserkundungsergebnisse unterschiedlicher Explorationsziele und geologischer Situationen. Seit 2000 ist das Vorauserkundungssystem in der Anwendung und zeigt, dass es unter den schwierigen und unterschiedlichen Bedingungen im mechanisierten Tunnelbau sowohl im Hartgestein als auch im Lockergestein im Dauereinsatz zuverlässige Ergebnisse erbringt. [source]

    High-dose Ara-C and beam with autograft rescue in R-CHOP responsive mantle cell lymphoma patients

    Mars B. Van't Veer
    Summary Mantle cell lymphoma (MCL) has a dismal outcome when treated with conventional chemotherapy. This single arm phase 2 study evaluated intensive consolidation treatment of patients with newly diagnosed MCL up to the age of 65 years, responsive to R-CHOP (rituximab, cyclophosphamide, oncovin, adriamycin, prednisolone). Endpoints for evaluation were toxicity, failure-free survival (FFS) and overall survival (OS). Eighty-seven patients were treated with three cycles of R,CHOP. Sixty-six patients responded to R-CHOP with at least a partial response, 62 continued protocol treatment with high-dose cytarabine (Ara-C; 2000 mg/m2, bid. over 4 d) and 61 patients received rituximab and stem cell harvest, followed by BEAM (carmustine, etoposide, Ara-C, melphalan) and autologous stem cell rescue. Non-haematological toxicity, grades III and IV, was seen in 8% of the patients after R-CHOP, in 22% after high-dose Ara-C and in 55% after BEAM. The overall response rate was 70% (complete response rate 64%, partial response rate 6%), FFS and OS at 4 years were 36 ± 7% and 66 ± 6%, respectively. The FFS and OS at 4 years from the evaluation after BEAM in the 61 R-CHOP responsive patients was 46 ± 9% and 79 ± 7%, respectively. In conclusion, high-dose Ara-C and BEAM with stem cell rescue in newly diagnosed MCL patients responsive to R-CHOP is a manageable treatment with respect to toxicity. This regimen leads to long-term, but probably not durable, remissions. [source]

    Damage Identification of a Composite Beam Using Finite Element Model Updating

    B. Moaveni
    As a payload project attached to a quasi-static test of a full-scale composite beam, a high-quality set of low-amplitude vibration response data was acquired from the beam at various damage levels. The Eigensystem Realization Algorithm was applied to identify the modal parameters (natural frequencies, damping ratios, displacement and macro-strain mode shapes) of the composite beam based on its impulse responses recorded in its undamaged and various damaged states using accelerometers and long-gage fiber Bragg grating strain sensors. These identified modal parameters are then used to identify the damage in the beam through a finite element model updating procedure. The identified damage is consistent with the observed damage in the composite beam. [source]

    Nano-characterization of Cast Structures by FIB-Tomography,

    F. Lasagni
    In this communication, the three dimensional architectures of different Al-Si-(Mg) alloys are analyzed using SEM (Scanning Electron Microscopy)/FIB (Focus Ion Beam), EDS (Energy Dispersive Spectroscopy)/FIB and SEM-EDS/FIB tomographic methods. Several aspects for the imaging and quantification of the results are discussed describing the advantages and limitations of the methods to resolve submicron structures. [source]

    Generation Mechanism and in situ Growth Behavior of ,-Iron Nanocrystals by Electron Beam Induced Deposition,

    W. Zhang
    Amorphous iron-containing deposits were formed on carbon films by electron beam induced deposition with a precursor of iron pentacarbonyl and alpha-Fe nanocrystals were grown around the target tip deposits when the electron beam irradiation time was longer than 1000,s. [source]

    Tuning Nanotubes: Beam to String Transition of Vibrating Carbon Nanotubes Under Axial Tension (Adv. Funct.

    On page 1753, the vibration properties of carbon nanotubes (CNTs) under axial tension are quantificationally studied by X. L. Wei et al. through a novel in situ method for precise and simultaneous measurement of the resonance frequency, the axial tension applied to individual CNTs, and the tube geometry. A gradual beam-to-string transition from multiwalled CNTs to singlewalled CNTs is observed; the CNTs can be tuned like a zither! [source]

    Beam to String Transition of Vibrating Carbon Nanotubes Under Axial Tension

    Xianlong Wei
    Abstract State-of-the-art nanoelectromechanical systems have been demonstrated in recent years using carbon nanotube (CNT) based devices, where the vibration of CNTs is tuned by tension induced through external electrical fields. However, the vibration properties of CNTs under axial tension have not been quantitatively determined in experiments. Here, a novel in situ method for precise and simultaneous measurement of the resonance frequency, the axial tension applied to individual CNTs and the tube geometry is demonstrated. A gradual beam-to-string transition from multi-walled CNTs to single-walled CNTs is observed with the crossover from bending rigidity dominant regime to extensional rigidity dominant regime occur much larger than that expected by previous theoretical work. Both the tube resonance frequency under tension and transition of vibration behavior from beam to string are surprisingly well fitted by the continuum beam theory. In the limit of a string, the vibration of a CNT is independent of its own stiffness, and a force sensitivity as large as 0.25,MHz (pN),1 is demonstrated using a 2.2,nm diameter single-walled CNT. These results will allow for the designs of CNT resonators with tailored properties. [source]

    Nanoscale Conducting Oxide Writing: Nanoscale Writing of Transparent Conducting Oxide Features with a Focused Ion Beam (Adv. Mater.

    ADVANCED MATERIALS, Issue 6 2009
    A conductive atomic force microscopy tip probes an embedded, optically transparent, electrically conducting oxide nanowire that was patterned on an indium oxide substrate using focused ion beam implantation. The nanowire is 160 nm wide, 7 nm deep, and theoretically limitless in length, connectivity, and shape. Nanowires of this type have potential application as interconnects in transparent electronics. Further details can be found in the article by Tobin Marks, Mark Hersam and co-workers on p.721. [source]

    Nanoscale Writing of Transparent Conducting Oxide Features with a Focused Ion Beam

    ADVANCED MATERIALS, Issue 6 2009
    Norma E. Sosa
    Embedded, optically transparent, electrically conducting oxide nanowires, and other patterns are written on highly resistive transparent metal oxide thin films with nanoscale spatial control using focused ion beam implantation. The resulting transparent conducting oxide features are 110-160 nm wide, 7 nm deep, and are theoretically limitless in length, connectivity, and shape. [source]

    A hybrid Padé ADI scheme of higher-order for convection,diffusion problems

    Samir KaraaArticle first published online: 8 SEP 200
    Abstract A high-order Padé alternating direction implicit (ADI) scheme is proposed for solving unsteady convection,diffusion problems. The scheme employs standard high-order Padé approximations for spatial first and second derivatives in the convection-diffusion equation. Linear multistep (LM) methods combined with the approximate factorization introduced by Beam and Warming (J. Comput. Phys. 1976; 22: 87,110) are applied for the time integration. The approximate factorization imposes a second-order temporal accuracy limitation on the ADI scheme independent of the accuracy of the LM method chosen for the time integration. To achieve a higher-order temporal accuracy, we introduce a correction term that reduces the splitting error. The resulting scheme is carried out by repeatedly solving a series of pentadiagonal linear systems producing a computationally cost effective solver. The effects of the approximate factorization and the correction term on the stability of the scheme are examined. A modified wave number analysis is performed to examine the dispersive and dissipative properties of the scheme. In contrast to the HOC-based schemes in which the phase and amplitude characteristics of a solution are altered by the variation of cell Reynolds number, the present scheme retains the characteristics of the modified wave numbers for spatial derivatives regardless of the magnitude of cell Reynolds number. The superiority of the proposed scheme compared with other high-order ADI schemes for solving unsteady convection-diffusion problems is discussed. A comparison of different time discretizations based on LM methods is given. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    CFD analysis of an oscillating wing at various reduced frequencies

    Farooq Umar
    Abstract The effect of various reduced frequencies has been examined for an oscillating aspect ratio 10 NACA 0015 wing. An unsteady, compressible three-dimensional (3D) Navier,Stokes code based on Beam and Warming algorithm with the Baldwin,Lomax turbulence model has been used. The code is validated for the study against published experimental data. The 3D unsteady flow field is simulated for reduced frequency values of 0.1, 0.2 and 0.3 for a fixed mean angle of attack position and fixed amplitude. The type of motion is sinusoidal harmonic. The force coefficients, pressure distributions and flow visualization show that at the given conditions the flow remains attached to the wing surface even at high angles of attack with no clear separation or typical light-to-deep category of dynamic stall. Increased magnitude of hysteresis and higher gradients are seen at higher reduced frequencies. The 3D effects are even found at midspan locations. In addition, the rate of decrease in lift near the wing tips compared with the wing root is not much like in the static cases. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Sediment preferences and size-specific distribution of young-of-the-year Pacific halibut in an Alaska nursery

    A. W. Stoner
    A combination of laboratory experiments and field surveys was used to test the hypotheses that responses to sediments change with fish size and that sediment grain-size is the predominant environmental factor affecting small-scale distribution in young-of-the-year (yoy) Pacific halibut Hippoglossus stenolepis. Laboratory tests showed that the smallest fish (31,40 mm LT) chose fine sediments (muddy and fine sands), fish 51,70 mm had high selectivity (primarily medium sand), and the largest fish (80,150 mm) were not selective although they avoided the largest grain-sizes (pebbles and granules). Sediment preferences were correlated with size-dependent burial capabilities. Beam trawl collections were made over a 6 year period in Kachemak Bay, Alaska, to examine the distribution of yoy Pacific halibut (14,120 mm LT) using small size classes (e.g. 10 mm intervals). Canonical correlation analysis showed that the per cent of sand in the sediment was a highly significant variable for all but one size and date combination. Catch per unit of effort (CPUE) for newly settled fish (<30 mm LT) was highest on very fine sand, fish 41,80 mm were most abundant on fine sand, and the largest yoy fish (81,120 mm) were abundant over a range of sediments from fine sand to mud. Except for the smallest fish, Pacific halibut in the field were associated with sediments somewhat finer than predicted from the laboratory experiments; however, virtually all were captured where they could bury easily. The ability of flatfish to bury and shelter in sediment is related to fish size; consequently, habitat associations shift rapidly during the first year of life. Habitat models for yoy flatfishes should consider size-dependent shifts in capabilities and preferences. [source]

    Physicochemical Changes in Alaska Pollock Surimi and Surimi Gel as Affected by Electron Beam

    ABSTRACT: Alaska pollock surimi and surimi gels (cooked) were subjected to various doses of electron beam (e-beam). Shear stress of surimi gels increased as the dose increased up to 6 to 8 kGy and then decreased. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed gradual degradation of myosin heavy chain as the dose increased. The degradation was slower for frozen samples. The integrity of actin was slightly affected by high doses (25 kGy). The amount of sulfhydryl groups and the level of surface hydrophobicity of Alaska pollock surimi decreased as the dose increased, suggesting formation of disulfide bonds and hydrophobic interactions. The sulfhydryl groups and hydrophobicity of surimi gels increased as the dose increased up to 6 kGy and then decreased. [source]

    Single linearly polarized, widely tunable Yb3+ -doped fiber laser with alternative polarization and wavelength

    D.-F. Liu
    Abstract A novel single linearly polarized, widely tunable Yb3+ -doped fiber laser with alternative two orthogonal polarization (wavelength) laser beams was proposed and demonstrated experimentally. Using a polarization beam splitting (PBS) as the separating of the two tunable laser beams in a linear Yb3+ -doped fiber cavity, the laser generates two alternatively tunable wavelength laser. Beam 1 is from 1001.9 nm to 1083.4 nm with single linear polarization and 368 mW (at 1030.1 nm) output power. Beam 2 is from 1000.0 nm to 1082.5 nm with 395 mW (at 1018.4 nm) output power and orthogonally polarized with beam 1. In addition, the laser can also work in widely tunable two wavelengths oscillating simultaneously. (© 2010 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

    Post-Synthesis Functionalization of (Meth)acrylate Based Monoliths via Electron Beam Triggered Graft Polymerization

    Matthias J. Beier
    Abstract Porous polymeric monoliths were prepared via electron beam triggered free radical polymerization of (meth)acrylates. Post-synthesis functionalization of these supports was accomplished via electron beam initiated free radical graft polymerization of methacryloyl-substituted NHC precursors. The grafted precursors were converted into the corresponding copper complexes. Cu-loadings were between 1.3 mg,·,g,1 and 1.5 mg,·,g,1. These supported catalysts were used in selected CO hydrosilylation and cyanosilylation reactions using a continuous flow setup. [source]

    Electron Beam Computed Tomography: Views of the Elephant

    Saul Schaefer MD Guest Editor
    No abstract is available for this article. [source]

    A Beam of Intense Darkness,

    Antonino Ferro
    First page of article [source]

    A Beam of Intense Darkness: Wilfred Bion's Legacy to Psychoanalysis by Grotstein, James

    Judith Pickering
    No abstract is available for this article. [source]

    A Beam of Intense Darkness: Wilfred Bion's Legacy to Psychoanalysis , By James Grotstein

    Meg Harris Williams
    First page of article [source]

    Electron Beam Induced Transformation of MoO3 to MoO2 and a New Phase MoO.

    CHEMINFORM, Issue 38 2004
    D. Wang
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    Accuracy of Linear Measurement Provided by Cone Beam Computed Tomography to Assess Bone Quantity in the Posterior Maxilla: A Human Cadaver Study

    Sophie Veyre-Goulet DDS
    ABSTRACT Purpose: The aim of this study was to assess, for implant placement in the posterior maxilla, the accuracy of linear measurements provided by cone beam computed tomography (CBCT) using an image intensifier tube and television (TV) chain as an X-ray detector despite a loss of contrast resolution. The NewTom® 9000 (Quantitative Radiology, Verona, Italy) was used to explore the posterior maxilla. Materials and Methods: Fourteen measurements were taken in three dry maxillaries. On every anatomical site, three fiducial markers were placed on the bony crest to define a plane. Dry maxillaries were submitted to CBCT imaging examination. The maxillaries were then sawn according to the previously defined planes, and bone height and width were assessed using a caliper. The same measurements were taken on images. Results: Clinical analysis demonstrated no difference between real measurements and image measurements. Conclusions: Although cadaver bone density may not correspond to the density of vital bone, this in vitro study indicates that CBCT images provided by technique using image intensifier tube and TV chain as an X-ray detector are reliable to define the bone volume of the posterior maxilla for the purpose of planning the implant axis. [source]

    Characterization of the Surface Properties of Commercially Available Dental Implants Using Scanning Electron Microscopy, Focused Ion Beam, and High-Resolution Transmission Electron Microscopy

    Tobias Jarmar PhD
    ABSTRACT Background:, Since osseointegration of the respective implant is claimed by all manufacturing companies, it is obvious that not just one specific surface profile including the chemistry controls bone apposition. Purpose:, The purpose was to identify and separate out a particular set of surface features of the implant surfaces that can contribute as factors in the osseointegration process. Material and Methods:, The surface properties of several commercially available dental implants were extensively studied using profilometry, scanning electron microscopy, and transmission electron microscopy. Ultrathin sections prepared with focused ion beam microscopy (FIB) provided microstructural and chemical data which have not previously been communicated. The implants were the Nobel Biocare TiUnite® (Nobel Biocare AB, Göteborg, Sweden), Nobel Biocare Steri-Oss HA-coated (Nobel Biocare AB, Yorba Linda, CA, USA), Astra-Tech OsseoSpeedÔ (Astra Tech AB, Mölndal, Sweden), Straumann SLA® (Straumann AG, Waldenburg, Switzerland), and the Brånemark Integration Original Fixture implant (Brånemark Integration, Göteborg, Sweden). Results:, It was found that their surface properties had differences. The surfaces were covered with crystalline TiO2 (both anatase and rutile), amorphous titanium oxide, phosphorus doped amorphous titanium oxide, fluorine, titanium hydride, and hydroxyapatite, respectively. Conclusion:, This indicates that the provision of osseointegration is not exclusively linked to a particular set of surface features if the implant surface character is a major factor in that process. The studied methodology provides an effective tool to also analyze the interface between implant and surrounding bone. This would be a natural next step in understanding the ultrastructure of the interface between bone and implants. [source]

    Nonlinear Damping Identification in Precast Prestressed Reinforced Concrete Beams

    P. Franchetti
    Integrated static and dynamic experiments were carried out on three precast PRC beam specimens. The static loading induced different levels of damage to the beams. At each damage level, impulsive loading was applied to the beams and the free vibration response was measured. The dynamic response data were processed using different methods including the multi-input multi-output (MIMO) curve fitting and the Hilbert transform techniques. A strong correlation is observed between the level of concrete damage (cracks) and the amount of nonlinear energy dissipation that can be modeled by means of quadratic damping. The nonlinear damping can be extracted from the free vibration response for each vibration mode. The proposed method is suited for quality control when manufacturing precast PRC members, and can be further extended for in situ detection of damage in concrete structures under ambient vibration. [source]

    A Study on the Effects of Damage Models and Wavelet Bases for Damage Identification and Calibration in Beams

    Vikram Pakrashi
    A numerical study has been performed in this article addressing these issues for single and multispan beams with an open crack. The first natural modeshapes of single and multispan beams with an open crack have been simulated considering damage models of different levels of complexity and analyzed for different crack depth ratios and crack positions. Gaussian white noise has been synthetically introduced to the simulated modeshape and the effects of varying signal-to-noise ratio have been studied. A wavelet-based damage identification technique has been found to be simple, efficient, and independent of damage models and wavelet basis functions, once certain conditions regarding the modeshape and the wavelet bases are satisfied. The wavelet-based damage calibration is found to be dependent on a number of factors including damage models and the basis function used in the analysis. A curvature-based calibration is more sensitive than a modeshape-based calibration of the extent of damage. [source]

    Survey of Theoretical Work for the Proposed HEDgeHOB Experimental Schemes: HIHEX and LAPLAS

    N. A. Tahir
    Abstract This paper presents a review of the theoretical work that has resulted in a scientific proposal on studies of High-Energy-Density (HED) states in matter using intense beams of energetic heavy ions that will be available at the future Facility for Antiprotons and Ion Research (FAIR) at Darmstadt [W.F. Henning, Nucl. Inst. Meth B 24 (2003) 725-729]. The proposal is named HEDgeHOB that stands for High Energy Density Matter Generated by Heavy Ion Beams. Two experimental schemes have been worked out for the HEDgeHOB experimental proposal, namely, HIHEX and LAPLAS. The first scheme allows for studies of HED states by isochoric and uniform heating of matter by an intense heavy ion beam that is followed by isentropic expansion of the heated material. Numerical simulations have shown that using the beam parameters that will be available at the FAIR, one can access all the interesting physical states of HED matter including an expanded hot liquid state, twophase liquid-gas region, critical point parameters and strongly coupled plasmas for all the materials of interest. The second scheme involves a low-entropy compression of a test material like hydrogen that is enclosed in a cylindrical shell of a high-Z material like gold or lead. The target can be driven by a hollow or a circular beam. This compression scheme relies on multiple shock reflection between the hydrogen-gold (lead) boundary and the cylinder axis. The hydrodynamic stability of the LAPLAS target has also been analyzed that shows that the implosion is completely stable to Rayleigh-Taylor and Richtmyer-Meshkov instabilities. LAPLAS implosion using a hollow beam is suitable for studying the problem of hydrogen metallization whereas the one employing a circular focal spot leads to physical conditions that are expected to exist in the interiors of the giant planets. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The Collapse Response of Sandwich Beams with Aluminium Face Sheets and a Metal Foam Core,

    V.L. Tagarielli
    Abstract Plastic collapse modes of simply supported and clamped sandwich beams have been investigated experimentally and theoretically, for aluminium face sheets and Alporas foam core. The effect of clamped boundary conditions is to induce axial stretching after the initial yield mechanism. Hence, face sheet ductility dictates the level of energy absorption of the beam. Numerical and analytical predictions are validated by the available experimental evidence. [source]

    Untersuchung nichtlinearer Schwingungseigenschaften zur zerstörungsfreien Zustandsprüfung am Beispiel von Stahlbetonbalken

    Markus Waltering Dipl.-Ing.
    Ingenieurbauwerke, im Speziellen Straßen- und Bahnbrücken, sind ein unverzichtbarer Bestandteil der Infrastruktur eines Landes. Um eine möglichst lange und wirtschaftliche Nutzung dieser Bauwerke zu ermöglichen, werden an Brücken regelmäßige Inspektionen durchgeführt. Die herkömmliche und am weitesten verbreitete Methode der Zustandsanalyse ist die visuelle Prüfung durch erfahrene Ingenieure. Dabei können jedoch ausschließlich äußere Anzeichen einer Schädigung festgestellt werden. Je nach Bauwerksgröße kann eine entsprechende Prüfung Tage bis Wochen in Anspruch nehmen. In besonderen Fällen kommen sehr kosten- und zeitintensive Belastungsversuche zum Einsatz. Seit einigen Jahren kommen immer häufiger Methoden zur Anwendung, welche die dynamischen Eigenschaften zur Zustandsbewertung nutzen. Im Rahmen dieses Aufsatzes werden Versuche an Stahlbetonbalken vorgestellt, bei denen die Untersuchung nichtlinearen Schwingungsverhaltens im Vordergrund steht. Damit soll ein Beitrag für die mögliche und zukünftige Beurteilung des nichtlinearen Schwingungsverhaltens zur Zustandsbewertung im Rahmen von Brückeninspektionen geleistet werden. The Investigation of Nonlinear Dynamic Behaviour for Non-Destructive Damage Assessment of Reinforced Concrete Beams The detection of damages in civil engineering structures and bridges in particular is mainly done by visual examination. However, defects as for instance partial rupture of a prestressing cable or fatigue cracks in reinforcement can not be visually observed. It is well known that damage changes dynamic structural parameters like eigenfrequencies, eigenmodes and damping. However, the sensitivity to small damages is sometimes low. Therefore, as an alternative the occurrence and evaluation of non-linear dynamic behaviour is considered. The basic idea is that non-linear dynamic effects increase with growing cracks under forced excitation. The implementation of this idea in the regular inspection program of bridges presupposes exact knowledge of the eigenfrequencies of the undamaged structure that are also supposed to be force dependent. This paper presents the results of an experimental approach with three reinforced concrete beams of different damage states investigating the non-linear behaviour due to the excitation force. [source]

    Ein Bemessungsansatz für zweiachsig durch Querkräfte beanspruchte Stahlbetonbalken mit Rechteckquerschnitt

    Peter Mark Dr.-Ing.
    Für Stahlbetonbalken mit Rechteckquerschnitt und üblichen zweischnittigen Bügeln wird ein Ansatz zur Bemessung gegen geneigt zu den Hauptachsen einwirkende Querkräfte abgeleitet und an Simulationsrechnungen und Experimenten verifiziert. Der Ansatz basiert auf dem der DIN 1045-1 zugrunde liegenden "Fachwerkmodell mit Rißreibung" und ergänzt zur Berücksichtigung einer Querkraftneigung die Gleichungen der Querkraftwiderstände nach DIN 1045-1 durch einfache Faktoren aus Geometrie- und Lastgrößen. Ein Beispiel zeigt, daß die Widerstände merklich abnehmen bzw. höhere Bügelbewehrungsmengen erforderlich sind, falls die Querkraft von einer hauptachsenparallelen Wirkungsrichtung abweicht. Design of Reinforced Concrete Beams with rectangular Cross Sections against biaxial Shear Forces An approach is presented to design reinforced concrete beams with rectangular cross sections and usual stirrups against shear forces that act inclined to the principal axes of the cross sections. It basis on the "truss model with crack friction" and adds supplementary terms to the equations of the shear resistances acc. to DIN 1045-1 to take account for shear force inclinations. Verifications to experimental as well as numerical data are given. An example shows that resistances evidently decrease , or higher amounts of stirrup reinforcement become necessary ,, if shear forces deviate from principal axes. [source]

    Damage Identification of a Composite Beam Using Finite Element Model Updating

    B. Moaveni
    As a payload project attached to a quasi-static test of a full-scale composite beam, a high-quality set of low-amplitude vibration response data was acquired from the beam at various damage levels. The Eigensystem Realization Algorithm was applied to identify the modal parameters (natural frequencies, damping ratios, displacement and macro-strain mode shapes) of the composite beam based on its impulse responses recorded in its undamaged and various damaged states using accelerometers and long-gage fiber Bragg grating strain sensors. These identified modal parameters are then used to identify the damage in the beam through a finite element model updating procedure. The identified damage is consistent with the observed damage in the composite beam. [source]

    A New Approach for Health Monitoring of Structures: Terrestrial Laser Scanning

    H. S. Park
    Three-dimensional (3D) coordinates of a target structure acquired using TLS can have maximum errors of about 10 mm, which is insufficient for the purpose of health monitoring of structures. A displacement measurement model is presented to improve the accuracy of the measurement. The model is tested experimentally on a simply supported steel beam. Measurements were made using three different techniques: (1) linear variable displacement transducers (LVDTs), (2) electric strain gages, and (3) a long gage fiber optic sensor. The maximum deflections estimated by the TLS model are less than 1 mm and within 1.6% of those measured directly by LVDT. Although GPS methods allow measurement of displacements only at the GPS receiver antenna location, the proposed TLS method allows measurement of the entire building's or bridge's deformed shape, and thus a realistic solution for monitoring structures at both structure and member level. Furthermore, it can be used to create a 3D finite element model of a structural member or the entire structure at any instance of time automatically. Through periodic measurements of deformations of a structure or a structural member and performing inverse structural analyses with the measured 3D displacements, the health of the structure can be monitored continuously. [source]