Anwendung der Zonenmethode für brandbeanspruchte Stahlbetonstützen

Die Heißbemessung von Stahlbetonstützen mit der Zonenmethode (Vereinfachtes Verfahren) ist nach Eurocode grundsätzlich möglich und in verschiedenen europäischen Normen bereits eingeführt. In Deutschland wird das Verfahren für die Stützenbemessung in Zukunft jedoch voraussichtlich abgelehnt, da sich die Ergebnisse teilweise nicht mit denen der anerkannten Allgemeinen Verfahren decken. Ein Grund für die Diskrepanz der Ergebnisse der verschiedenen Methoden liegt nach Einschätzung der Autoren in der teilweise nur unzureichenden Dokumentation bzw. Regelung der Zonenmethode. Dass z. B. die Zonenmethode als Verfahren der Plastizitätstheorie angelegt ist, jedoch als nichtlineares Verfahren verwendet wird, führte bereits zu wesentlichen Fehlinterpretationen bzw. Missverständnissen. Dieser Aufsatz zeigt daher eine kurze Darstellung der ursprünglichen Annahmen sowie eine Herleitung der Zonenmethode nach Hertz. Im Hauptteil des Aufsatzes wird anhand von dokumentierten Eichbeispielen gezeigt, wie die Zonenmethode für Druckglieder in der Praxis anzuwenden ist, damit die Traglast und das Last‐Verformungsverhalten bezogen auf die Allgemeinen Verfahren ausreichend genau bestimmt werden können. Use of a Simplified Method (Zone Method) for Concrete Columns Exposed to Fire Eurocode 2 provides a fire resistance check for concrete columns called zone method (simplified calculation method). Some European countries already allow this check. Germany will probably reject this method for concrete columns, as the results from the zone method partly differ from the accepted advanced method. In the authors' opinion, one reason for the differences might be lack of documentation or lack of detailed rules for the zone method. Using the zone method as a nonlinear method – even though it is based on the assumptions of plastic theory – already lead to decisive misinterpretations or misunderstandings. Hence, this article shows briefly the original assumptions and derivation of basic formulas for the zone method according to Hertz. The use of the zone method for compression members is demonstrated with documented calibrating examples. It is displayed, how to calculate the ultimate load and the load‐bearingbehaviour with adequate accuracy.     

Limit-State Surface Element Method: Application to Fatigue Reliability with NDE Inspections

A new method, named the limit-state surface element (LSSE) method, for problems in structural reliability is presented. The method is based on discretization of the limit-state surface into a finite number of elements. This allows for better representations of the failure surface in regions of high curvature than is possible with standard FORM techniques. The reliability is estimated as a sum of integrals over subdomains in the space of standard normal variables associated with the surface elements. Several benchmark problems are presented to demonstrate the accuracy and utility of the method, and a problem in fatigue reliability with NDE inspections is presented as a practical application of the method and a demonstration of the potential interrelations between QNDE and reliability assessment.     

Aromatic Phosphonates: A Novel Group of Emitters Showing Blue Ultralong Room Temperature Phosphorescence

In recent years, there has been a growing interest in purely organic materials showing ultralong room-temperature phosphorescence with lifetimes in the range of seconds. Still, the longest known phosphorescence lifetimes are only achieved with crystalline systems so far. Here, a rational design of a completely new family of halogen-free organic luminescent derivatives in amorphous matrices, displaying both conventional fluorescence and phosphorescence is reported. Hydrogen bonding between the newly developed emitters and an ethylene-vinyl alcohol copolymer (Exceval) matrix, which efficiently suppresses vibrational dissipation, enables bright long-lived phosphorescence with lifetimes up to 2.6 s at around 480 nm. The importance of the chosen matrix is shown as well as the implementation in an organic programmable luminescent tag.     

Design and microfabrication of a polymer membrane-based submicron scale electrophoretic flow detector for biomedical applications

This study demonstrates the design and microfabrication of single cylindrical submicron-sized pores in 1 μm-thick PMMA membranes, and their integration and assembly into all-polymeric electrophoretic detectors. Pore sizes vary from 200 to 600 nm. Fabrication includes electron beam lithography of the pore and mechanical microfabrication and assembly of the remaining detector system, using UV-curing glues and a silicon sacrificial substrate wafer. Initial electrophoretic translocation experiments have been performed for various potassium chloride (KCl) electrolyte concentrations between 0.1 and 1 M. Experiments prove that the detector system is hermetically sealed, that the pores are capable of sustaining an open pore current, and that they respond with a steady and low-noise signal. The same experiments have also been applied to analyze the pore metrology, and revealed that submicron pore sizes have been underestimated by roughly 150 nm.     

In situ diagnostic capabilities for beam position and beam intensity monitoring at SyLMAND

SyLMAND, the Synchrotron Laboratory for Micro and Nano Devices at the Canadian Light Source, consists of a dedicated X-ray lithography beamline on a bend magnet port, and process support laboratories in a cleanroom environment. The beamline comprises a double mirror system with flat, chromium-coated silicon mirrors operated at varying grazing angles of incidence for spectral adjustment by high energy cut-off. We present in this paper, the in situ diagnostic components inside the vacuum vessel upstream and downstream of the mirrors that allow for monitoring the incident beam and the reflected beam after first, second, and both mirrors. Four fly wire systems are used for beam position monitoring and intensity measurements. Additionally, four detector plates mounted on and moving with the mirror bodies are used to determine the position of the mirror surfaces with respect to the beam. First experimental results verify the capabilities of the system by showing good agreement between measured and calculated data.     

Numerical simulation of thermal distortions in deep and ultra deep X-ray lithography

 One major process step in deep X-ray lithography is the exposure of the resist with synchrotron radiation. High energy photons are absorbed in mask, resist and substrate. About 95% of this energy is deposited as thermal heat [Schweizer (1997)]. This may lead to a temperature rise in the system and result in thermal distortions during the patterning process. A sample layout is used to determine the distortions during irradiation. Typical radiation parameters of the ELSA storage ring at Bonn University (2.7 GeV, 35 mA) and material properties are applied to simulate the heat effects. Mask membranes made of titanium or beryllium are modeled to irradiate PMMA layers of 200 and 2500 μm thickness. Copper is used as substrate material. Mask support and the bottom of the substrate are cooled to 21 °C as the system is scanned through the synchrotron beam. In the case of 200 μm PMMA and titanium mask membranes, mask temperatures increase to 40.1 °C, whereas only 22.3 °C are reached if beryllium masks are simulated. Maximum distortions are 0.74 μm for Ti-masks and 0.03 μm for Be-masks. With increasing resist thickness, the incident synchrotron radiation power as well as the temperature rise are reduced. In the case of 2500 μm thick PMMA, temperatures of 21.45 °C are simulated. Received: 10 August 2001/Accepted: 24 September 2001 This paper was presented at the Fourth International Workshop on High Aspect Ratio Microstructure Technology HARMST 2001 in June 2001.     

Epidemiological comparisons of problems and positive qualities reported by adolescents in 24 countries.

In this study, the authors compared ratings of behavioral and emotional problems and positive qualities on the Youth Self-Report (T. M. Achenbach & L. A. Rescorla, 2001) by adolescents in general population samples from 24 countries (N = 27,206). For problem scales, country effect sizes (ESs) ranged from 3% to 9%, whereas those for gender and age ranged from less than 1% to 2%. Scores were significantly higher for girls than for boys on Internalizing Problems and significantly higher for boys than for girls on Externalizing Problems. Bicountry correlations for mean problem item scores averaged .69. For Total Problems, 17 of 24 countries scored within one standard deviation of the overall mean of 35.3. In the 19 countries for which parent ratings were also available, the mean of 20.5 for parent ratings was far lower than the self-report mean of 34.0 in the same 19 countries (d = 2.5). Results indicate considerable consistency across 24 countries in adolescents' self-reported problems but less consistency for positive qualities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time-domain boundary element analysis of dynamic near-tip fields for impact-loaded collinear cracks

A time-domain boundary integral equation method has been developed to calculate elastodynamic fields generated by the incidence of stress (or displacement) pulses on single cracks and systems of two collinear cracks. The system of boundary integral equations has been cast in a form which is amenable to solution by the boundary element method in conjunction with a time-stepping technique. Particular attention has been devoted to dynamic overshoots of the stress intensity factors. Elastodynamic stress intensity factors for pulse incidence on a single crack have been computed as function of time, and they have been compared with results of other authors. For collinear macrocrack-microcrack configurations the stress intensity factors at both tips of the macrocrack have been computed as functions of time for various values of the crack spacing and the relative size of the microcrack.     

Radial matrix cracking and interphase failure in transversely loaded fiber composites

Radial matrix cracking and interphase failure for transverse loading of a hexagonal array fiber composite are investigated by: (1) modeling the interphase by a layer of radial and circumferential spring elements, (2) adopting a tensile stress criterion for initiation of matrix cracking, and (3) employing a strain-energy density criterion for interphase failure. The mechanical behavior of the composite is defined in terms of geometrical, stiffness and strength parameters. Stresses on the microlevel have been calculated. Under the assumption that the failure mechanisms follow the periodicity of the composite, two scenarios related to different values of the strength parameters have been investigated. In the first scenario matrix cracking occurs first, followed by interphase failure. In the second scenario interphase failure is followed by matrix cracking. Typical results are displayed graphically.     

Fabrication of RF MEMS variable capacitors by deep X-ray lithography and electroplating

Radio frequency micro electro-mechanical systems (RF MEMS) vertical cantilever variable capacitors fabricated using deep X-ray lithography and electroplating are presented. Polymethylmethacrylate (PMMA) layers of 100 μm and 150 μm have been patterned and electroplated with 70 μm and 100 μm thick nickel. A 3 μm thick titanium layer was used as plating base as well as etch time-controlled sacrificial layer for the release of the cantilever beam. The parallel plate layout includes narrow gaps and cantilever beams with an aspect ratio in nickel of up to 60 for 1 mm long features. Auxiliary structures support the beams and gaps during the processing. Room temperature electroplating significantly reduces the risk of deformations compared to the standard process temperature of 52°C. The capacitors operate in the 1–5 GHz range, and demonstrate good RF performance, with quality factors on the order of 170 at 1 GHz for a 1 pF capacitance.